Duration: 10/01/2020 to 09/30/2025

Administrative Advisor(s):

NIFA Reps:

Non-Technical Summary

Statement of Issues and Justification

The 2017 Census of Agriculture reported 101,387 farms with sheep. The value of sheep marketed was $711,899,000  from 4.1 million animals . In 2018, the U.S. imported approximately 272.6 million pounds of lamb and mutton while exporting just 5.8 million pounds (USDA ERS, 2019).  Per capita consumption of lamb is low relative to beef and pork, but niche markets are growing. In addition, national efforts are underway to reverse the decline in the American lamb industry (American Sheep Industry, 2014) through both traditional and non-traditional marketing channels. Meanwhile, the sheep industry continues to struggle with animal health concerns, economic issues, global competitiveness and consumer trends. These issues are far greater in scope than can be addressed by individual research stations. Collaborative efforts are needed to generate new knowledge for a more sustainable industry. The need for collaborative work is greater than ever as research stations are losing, and not replacing, research and extension faculty with sheep expertise. New technology can be applied to improve efficiency and to compete more effectively in a world-wide market. Research results benefit the sheep industry and consumers by increasing efficiency and improving product quality. A viable sheep industry will contribute to sustainable agricultural practices and provide economic stability to rural communities.

The NC-214 project members are uniquely suited to address these issues. Members are trained in genetics, reproduction, nutrition, meats, animal management and health, and rangeland management. This diversity of training is the strength of this research group and brings depth and perspective to investigations of complex issues. NC-214 will be the only multi-state research project in the U.S. that focuses on sheep with emphasis on genetics, reproduction, animal health, carcass leanness, meat quality, and milk production in wool and hair sheep. 

Objectives of NC-214 are well aligned with research priorities identified by the American Sheep Industry Association and the Agricultural Research Service of USDA. They also are compatible with recommendations and strategies of The American Lamb Industry Roadmap Project (American Sheep Industry, 2014), which was designed to strengthen the sheep sector of the U.S. that produces lambs for meat. The overall research goal of NC-214 is to continue developing integrated food-animal management and animal health systems that support efficient, competitive and sustainable production of safe and wholesome food consistent with animal and environmental well-being. This includes: 1) Developing and evaluating methods to improve reproductive efficiency; 2) Developing strategies to improve efficiency of lean lamb growth and meat quality; 3) Evaluating genetic resources, nutrient requirements and production systems for lamb, wool, and milk production; 4) Developing profitable and sustainable production systems that address grazing strategies for animal health and well-being, and for ecosystem health, biological control of invasive plants and wildfire mitigation. Planned research of NC-214 is consistent with the components of National Program 101 (Food Animal Production Action Plan) of ARS and National Program 103 (Animal Health Strategic Vision).

The sheep industry is fortunate to have significant adaptability to market conditions, due to a wide array of breed resources and diverse production systems. A common approach will be evaluation of breeds. In many experiments, two or more common breeds will be compared at different institutions. Also, research to evaluate one or more hair breeds of sheep (Dorper, White Dorper, Katahdin, St. Croix and Barbados Blackbelly) will be done at several institutions, including Kentucky, ARS-MARC, North Dakota, Texas, Utah, Virginia State, and ARS-Booneville. Use of common breeds will create linkages across experiments, effectively allowing comparison of more breeds than evaluated in any single experiment. This information will help the industry to systematically use the most appropriate breeds in systems that produce market lambs. All institutions will be involved in further developing profitable and sustainable production systems with members in Arkansas, ARS-MARC, Rhode Island, Utah, West Virginia and Wyoming continuing efforts to develop methods for more effectively managing internal parasites as well as noxious weeds. Finally, all member institutions will increase efforts toward dissemination of research results and information to other universities, regulatory agencies and producers. This will help to address the attrition of research and extension personnel with sheep expertise. The overall impact is expected to improve the competitiveness of the U.S. sheep industry with other major sheep producing countries.

 

Related, Current and Previous Work

A related project in NIMSS, SCC81, addresses sustainable sheep and goat production in the Southeastern U.S.  Both projects address grazing sheep, but the SCC-81 has a greater emphasis for pasture/forage and silvopasture systems that include goats than the current project, and focuses specifically on the Southeastern U.S. The SCC-81 parasite control project does not include use of vaccines and specifically targets pasture and forages that can be used to minimize internal parasites. There is overlap in out-of-season breeding, but the SCC-81 project collaborators may use synchronization technology and have smaller flocks, which limit flexibility in experimental design.  There were several grazing projects listed in NIMSS, but they dealt primarily with beef or dairy cattle, or were focused on nutrient cycling of pasture system.

 Objective 1:  A priority of the American Sheep Industry (www.sheepusa.org) is to increase national flock productivity and to increase out-of-season lamb production to decrease the seasonality of  domestic sheep meat availability (Miller et al., 2016).  The reproductive seasonality of sheep remains a major constraint to overcome the seasonality of lamb production.  There are sheep genetics that exist, however, that are less seasonal in nature (aseasonal breeds), either selected specifically for this trait in higher latitudes (i.e., Finn, Dorset, Romanov) or as found in regions closer to the equator that are naturally less reproductively entrained to day length (i.e., Merinos and their derivatives from Spain or various hair breeds of West African decent) (Notter and Copenhaver, 1980; Fahmy, 1990; Casas et al., 2005).  Despite this aseasonal capacity, both conception rate and litter size are often reduced during long day seasons (suboptimal breeding season)  in wool breeds (Notter, 1992; Lewis et al., 1996); and hair breeds (Schoeman and Burger, 1992; Brown and Jackson, 1995; Burke, 2005; Wildeus, 2005). Aseasonal wool breeds appear to be relatively more influenced by nutritional cues in regulating reproductive outcomes (Hötzel et al., 2003; Forcada and Abecia, 2006).  It is not known if this extends to hair sheep and nutritional management of sheep in accelerated and annual birth management systems  has not been optimized for reproductive outcomes regardless of genotype.  

Male biostimulation or use of the “ram or male effect” has been well documented to synchronize estrus and to induce ovulation in ewes in the transition period between estrus and anestrus (Ungerfeld et al., 2004).  The ram effect alone has been demonstrated to be as effective as progesterone/gonadotropin therapy in improving conception rate during the suboptimal breeding season (Inskeep and Lewis, 2009).  It is less clear however if the ram effect can induce ovulation of ewes deep in anestrus or all aseasonal genotypes.  Furthermore, there has not been extensive research to optimize the ram effect in accelerated sheep production systems that seek to reduce the birthing interval to 7 to 8 months.  

The attainment of puberty in sheep is influenced by body composition, photoperiod  and genetics (Foster et al., 1988; Nieto et al., 2019). Therefore, replacement ewe lambs born in a season that allows exposure to short day photoperiod at an earlier age reach puberty faster as do those that are fed a high plane of nutrition.  It is accepted that ewe lambs bred to lamb in their second year of life have higher lifetime productivity (Hulet et al., 1969),  however this has not been investigated in prolific breeds nor has it been refined  to understand how this may apply to current production system with aseasonal and/or shortened birth intervals or in ewes that are fed on higher planes of nutrition. 

A liquid semen AI system has received increased attention in sheep, due to inability to perform transcervical insemination in ewes and the need for use with frozen-thawed semen. In Europe and South America, localized co-ops and networks have developed the use of short-term stored liquid semen and vaginal AI. Such systems have not been evaluated to any great extent in the U.S., but could be of benefit to introduce unique and superior germplasm, with no need for live animal transport and associated biosecurity concerns.  Use of liquid semen vaginal AI applied in a small farm setting within 3 to 4 hours driving distance has resulted in pregnancy rates of 40 to 50% (O’Brien and Wildeus, 2019), however, to be more widely applicable the use of overnight shipment of liquid stored semen needs to be explored.

 Objective 2:

The estimated per capita consumption  of lamb and mutton products in the U.S. has continued to decrease over the last several decades from 2.1 lb/person in 1970 to 0.8 lb/person in 2018 (USDA ERS, 2018). In comparison, the average American consumed 78, 55, and 48 pounds of poultry, beef, and pork in 2018, respectively. Furthermore, more than 50% of the lamb that is consumed in the U.S. is imported. Increasing the consumption of domestic lamb is multifaceted but will be greatly impacted by enhancing production efficiency and product quality.

Seasonality of production is an inherent issue unique to the lamb industry as approximately 85% of lambs in the US are born in the first five months of the year (USDA APHIS, 2014a). Ideally, lambs are harvested between 6 and 12 mo of age leading to shortages in lamb supply from May to August (US Lamb Resource Center, 2018). However, the lamb packing industry requires a continual supply, and in order to compensate for shortages feedlots must extend days on feed, which pushes lambs beyond weights appropriate for their frame size. Sheep industry working groups have identified lamb products excessive in fat as a major threat to consumer satisfaction and demand for American lamb (American Sheep Industry, 2014). Currently, the U.S. lamb industry follows a value-based pricing system on a limited basis with the primary emphasis on hot carcass weight, leaving the packer to bear the additional expenses generated from excessively large lamb carcasses. To date, there has been no quantification of the accrued costs of excessively finished lamb carcasses in the U.S. processing sector. Furthermore, detailed surveys of pre- and post-harvest commercial lamb characteristics are presently lacking, which prevents researchers from clearly identifying management, nutritional, and genetic factors contributing to variation in lamb quality.

Because most U.S. lambs are marketed on a live weight basis, selection emphasis has directly or indirectly favored larger, faster growing sheep. For example, historical data collected and analyzed on ram lambs enrolled in the Wyoming central performance test estimated that BW and average daily gain throughout the feeding period increased by 22.7 kg and 0.16 kg/d, respectively, over the past 50 yr (Burton et al., 2015). However, essentially no selection pressure has focused on directly improving feed efficiency in sheep. While the National Sheep Improvement Program (NSIP) currently calculates across-flock estimated breeding values (EBV) for pre- and post-weaning lamb BW and ultrasound loin and backfat depth, no direct measures of lamb feed efficiency are available. The major reason for this is that quantifying individual feed intake requires specialized equipment that is cost-prohibitive for sheep producers. Still, improving feed efficiency greatly enhances the sustainability of sheep production and efforts must be made to incorporate it into large-scale genetic evaluations. 

Making meaningful improvements in feed efficiency of sheep will require a consistent methodology to accurately identify efficient individuals. Residual feed intake (RFI) is quickly becoming the preferred measurement of efficiency in many species due to its inherent independence of most other important production traits such as BW and average daily gain. RFI is calculated by subtracting expected intake from actual intake and has been estimated to be lowly to moderately heritable in U.S. sheep flocks (0.11-0.26) (Snowder and Van Vleck, 2003; Cammack et al., 2005). A recent study at West Virginia University calculated RFI utilizing a Growsafe™ system. At the start of the Texel trial, lambs were separated by sex. After a period of adaptation, Texel average intake was determined over a period of 27 consecutive d and used to calculate individual RFI within the test population. Observable ranges of RFI ( -0.62 to +0.62) were observed in the Texel lambs. At the start of the Katahdin trial lambs were separated by sex and FEC treatment. After a period of adaptation, Katahdin average intake was determined over a period of 42 consecutive d and used to calculate individual RFI within the test population. Observable ranges of RFI ( -0.53 to +0.50) were observed in the Katahdin lambs as well. In both feeding trials RFI appeared to be normally distributed, an important assumption for the genetic models utilized by NSIP.  

Recent reports suggest that the flavor of lamb is the largest contributor to consumer acceptance (Pleasants et al., 2005; Pethick, 2006) which is unique among red meat products. Tenderness is often cited as the most important indicator of eating quality among beef consumers, but lambs are slaughtered at such young ages that most produce tender meat.  Sheep meat has a distinct flavor profile compared to beef or pork (Pearson et al., 1973) and, at high concentrations, certain compounds can create negative eating experiences. Still, acceptance of varying degrees of lamb flavor intensity is dependent upon consumer demographics and prior exposure (Prescott et al., 2001). Therefore, consumer demand for lamb could be improved by marketing cuts according to their expected flavor profile. It is well known that sex, finishing diet, and harvest age can influence the flavor of lamb (Elmore et al., 2000; Duckett and Kuber, 2001). While few reports have attempted to mitigate potential off flavors in sheep meat through manipulating finishing diets (Kerth et al., 2019), there is evidence that plant secondary compounds can enhance certain flavor attributes (Schreurs et al., 2008; Whitney and Smith, 2015). While most reports suggest that breed is not a consistent source of variation in lamb flavor (Duckett and Kuber, 2001), less is known about the degree of genetic variation in flavor compounds within breeds. To analyze genetic and non-genetic effects contributing to lamb flavor and other carcass characteristics, well phenotyped and pedigreed populations of sheep need to be established and evaluated.

 Objective 3:

Flocks enrolled in the National Sheep Improvement Program (NSIP, www.nsip.org) are provided with across-flock estimated breeding values (EBV) for many economically important traits. These EBV enable producers to select replacement animals according to their predicted genetic merit for maternal, terminal, wool, and health traits. In addition to single trait EBV, NSIP also has developed several multiple-trait indexes. While NSIP EBV/indexes are extremely valuable for seedstock and commercial sheep producers, they can be improved through inclusion of additional economically relevant traits and creating multiple-trait indexes for more specific production environments. A few traits that are of interest to sheep producers but that NSIP does not currently support include: FAMACHA© score, ewe longevity, and out-of-season/accelerated lambing potential. 

FAMACHA© anemia score is an indicator of internal parasite resilience and is a common husbandry practice utilized by producers to identify individuals in need of anthelmintic treatment. While quantifying fecal egg counts (FEC) requires producers to have access to a microscope and other specialized equipment or pay for laboratory analyses, phenotyping for FAMACHA© is rapid and low-cost. Developing NSIP EBV for FAMACHA© score would provide more sheep producers with tools for selecting sheep that are less dependent on chemical dewormers. Previous researchers estimated that FAMACHA© score is heritable (0.11-0.41) and favorably genetically correlated with FEC (0.66-0.85) (Riley and Van Wyk, 2009; Cloete et al., 2016; Ngere et al., 2017). This suggests that the FAMACHA© score can be effective at identifying genetic resistance/resilience to internal parasitism.

Culling ewes prior to the end of their normal productive life reduces enterprise profitability because the fixed costs associated with raising replacements to reproductive age are spread over fewer lamb crops. The most common reason for culling ewes prematurely in the U.S. include: failure to lamb (7.7% of ewes culled), teeth problems (7.6%), hard bag syndrome (7.1%), and mastitis (6.7%) (USDA APHIS, 2014a). Ewe stayability/longevity can be defined as age at culling or  whether a ewe was present or absent at a particular age and has been estimated to be lowly to moderately heritable (0.0 to 0.27) (Borg et al., 2009; Mekkawy et al., 2009; Lee et al., 2015). From a genetic analyses and selection standpoint, longevity presents challenges as ewes can be culled for many reasons (e.g., fertility, body condition, disease) and they only express the trait once when they are (hopefully) comparatively old. For these reasons, it would be beneficial to identify traits that can be measured at younger ages that are indicative of ewe longevity. Results from Mekkaway et al. (2009) suggested that ewe age at culling/death was not genetically correlated with subjectively (mouth score, structural soundness, body condition) or objectively (BW, ultrasonic fat/muscle depth) measured traits recorded when they were lambs (~195 d of age). Still, refined subjective scales for udder morphometric traits (Casu et al., 2006) and objectively characterizing mouth structure could be useful to improve components of ewe longevity. For example, teat and udder characteristics have been estimated to be genetically correlated with indicators of mammary health in dairy (Legarra and Ugarte, 2005; Casu et al., 2010) and non-dairy sheep (McLaren et al., 2018). Additionally, early studies suggested that incisor wear and retention rate are heritable (0.39 to 0.80) (Purser et al., 1982; Meyer et al., 1983). Therefore, genetic variation in ewe longevity exists but traits/analyses need to be refined before they can be implemented NSIP.

Sheep are most reproductively active during periods of decreasing day length (i.e., fall months). This, combined with producer attempts to synchronize the greatest ewe nutritional demands with seasonal forage growth and quality, largely explains why ~85% of U.S. lambs are born from January to May (USDA APHIS, 2014b). Seasonality of lamb production limits consistent cash flow for sheep producers and can lead to downstream negative effects on carcass quality if the supply of lamb is to remain relatively constant throughout the year. Out-of-season breeding and accelerated lambing programs can improve the seasonality of lamb production. It has been estimated that ewe and ram ability to breed during spring months is lowly heritable (0.07 to 0.11) (al-Shorepy and Notter, 1996) but has been improved through selection (al-Shorepy and Notter, 1997). Genetic markers may help (Mateescu and Thonney, 2010; Posbergh et al., 2017; Posbergh et al., 2019).  Additionally, ewe fertility and prolificacy in accelerated lambing systems (5 lambing events in 3 years or 3 lambing events in 2 years) is largely influenced by non-genetic factors such as age, season, and length of time from previous lambing (Lewis et al., 1996). The current structure of the NSIP flock performance recording software doesn’t allow for ewe reproductive traits to be analyzed for separate seasons, and only one lambing event per calendar year can be recorded. However, results from experimental flocks can be used to develop EBV for out-of-season/accelerated lambing potential from genetically correlated traits.

Single trait selection is rarely recommended in livestock breeding and it is important to understand genetic and non-genetic relationships among traits in order to breed for more profitable and sustainable flocks in a given production system. Selection indexes optimally combine EBV from multiple traits by weighting each by their economic value. The economic value of a trait describes the change in enterprise profit resulting from a one unit increase in the trait’s average EBV, while holding all other traits constant. The bioeconomic model is a common approach to derive economic values for traits in livestock species and uses a system of equations to describe the life cycle of an animal in terms of inputs and outputs as functions of biological traits and economic parameters. NSIP currently has indexes for maternal performance and total productivity in Western rangeland production systems (Borg et al., 2007). However, existing indexes need to be routinely reevaluated under more current market conditions and developing new indexes for specific production systems should be considered. 

Sheep milk production is mostly seasonal, starting after lambing in late winter or spring with pasture as the primary feed. This produces a gap in marketing strategies for sheep milk products. Sheep from the two main dairy breeds in the US, East Friesian and Lacaune, have not been selected to lamb out of season and ewes produce relatively low amounts of milk toward the end of lactation. Dorset and Finnsheep in the Cornell flock have been selected for 40 years to lamb frequently on the STAR system (5 lambings per ewe in 3 years). Sheep at Michigan State University include some of the Cornell genetics and also are selected to lamb more frequently than once per year. Cornell Finn x Dorset ewes milked on the STAR system produced nearly as much milk as dairy breed sheep in early lactation, but were much less persistent, with low milk production at the end of each 73-d lactation (Kochendoerfer and Thonney, 2018). Subsequently, it was demonstrated that ¼ East Friesian x ¾ Finn x Dorset ewes had much greater persistency to 110 days and were able to successfully rebreed at 97 DIM (Kochendoerfer and Thonney, 2019). Incorporating accelerated lambing genetics with dairy sheep genetics to allow ewes to lactate for three 120-d lactations in two years could optimize year-round milk production.

 Objective 4:

The conventional method used to control gastrointestinal nematode infections (GIN) is the use of chemical anthelmintic (deworming) drugs. With the growth of anthelmintic resistance in GIN, alternative methods are needed for GIN control.

A nematode trapping fungus, Duddingtonia flagrans, can be used in small ruminants for parasite control (Githigia et al., 1997; Waller et al., 2001; Peña et al., 2002; Terrill et al., 2004) and has recently been commercialized in the U.S. (BioWorma® or Livamol® with BioWorma®; International Animal Health Products Pty. Ltd., Australia).  Resting spores (chlamydospores) of this nematode-trapping-fungus incorporated in a feed supplement pass through the digestive tract of livestock and are deposited in the feces (Larsen et al., 1992; Grønvold et al., 1993; Faedo et al., 1997; Larsen et al., 1998; Larsen, 2000).  In feces, the fungus develops along with the larvae on pasture, trapping and killing the larvae, including Haemonchus contortus (Fontenot et al., 2003; Waghorn et al., 2003; Chandrawathani et al., 2004).  Thus, pasture infectivity of H. contortus is greatly reduced in sheep pastures with D. flagrans feeding (Fontenot et al., 2003; Chandrawathani et al., 2004). Manufacturer recommendations are to feed BioWorma daily in a supplement, but not all flocks feed daily. It is not known whether spores can be mixed with minerals and offered weekly.

An antiparasitic effect has been demonstrated in sheep and goats consuming condensed tannin containing forages.  One of the bioactive components of condensed tannins are proanthocyanidins (PAC). Cranberry vines contain many condensed tannins, with biological activity (Howell, 2007) that hold promise as a natural anthelmintic for GIN.  We will investigate the use of a pelleted cranberry vine (CV) pellet against GIN infections of sheep grazing GIN infected pastures.  Investigators at URI have completed the initial evaluation of cranberry PAC in several tests (in vitro and in vivo) routinely used to evaluate the effect of compounds on GIN. Cranberry PAC showed anthelmintic activity against L1 and adult H. contortus in vitro after 24 h incubation in solutions containing concentrations of PAC similar to those used in other studies of bioactive condensed tannins (Barone et al., 2018). Twenty-eight grams of cranberry vine powder, administered for three consecutive d, suppressed the FEC for one wk in lambs experimentally infected with H. contortus (Barone et al., 2018). Feeding 500 g CV/d to lambs experimentally infected with H. contortus suppresses the FEC (unpublished data). We propose to extend these studies to determine the anti-parasitic efficacy against GIN of feeding a CV supplement to lambs grazing GIN infected pasture. 

Preliminary data from WVU have indicated that parasite-resistant sheep (St. Croix) preferentially generate antibody to a common protein found in H. contortus L3-stage larvae and its cuticle when compared to a parasite-susceptible breed (Suffolk). Currently, no vaccine is available in the US to aid producers in controlling H. contortus infection. Thus, a critical need exists to determine the efficacy of vaccination using protein derived from larval stages of H. contortus.  Such information would be critical in developing preventatives that would reduce the impact this parasite has on sheep health and productivity.

  Currently, a single vaccine exists against H. contortus and its availability is limited to Australia. BarberVax is a subunit vaccine made up of two worm native hidden gut proteins and Quil A adjuvant. Because the vaccine is specific to hidden internal gut proteins of the parasite, boosters are required upwards of 3 times to maintain protection. In addition, BarberVax must be administered to sheep every season for protection. This vaccine is not yet available in the US, as it may not even work well enough to warrant the expense of FDA approval.  Work from WVU has shown that H. contortus tropomyosin may serve as a vaccine candidate.  This protein is ideal because of its tissue distribution, including the L3 cuticle and whole larval homogenate.  And is preferentially bound by serum from parasite-resistant vs susceptible sheep. Development of an effective vaccine against H. contortus will improve producer profitability, reduce reliance on chemotherapeutics and improve animal health.

Invasive plants like medusahead (Taeniatherum caput-medusae (L.) Nevski) or ventenata (Ventenata dubia) represent significant threats to rangeland sustainability and livestock operations (Miller et al., 1999; Davies and Johnson, 2008) in the western US. They decrease wildlife habitat, plant diversity, and increase the frequency of fires (Davies and Johnson, 2008). These impacts are further compounded by the fact that traditional mechanical, cultural, and chemical control techniques are often unsuccessful. Targeted grazing approaches represent a sustainable alternative to weed control since sheep can use the weed as forage while reducing its abundance in the plant community. Nevertheless, grazing weeds may be detrimental to the animal, and intake may be constrained, given that these plants are in general of low nutritional value. Supplemental nutrients have the potential to increase weed use by livestock because nutrients enhance digestion processes and increase tolerance to plant toxins (Montes-Sánchez et al., 2017). Thus, one of the objectives of this proposal entails determining whether improved pastures or supplements would provide the appropriate nutrients to enhance consumption of weeds by sheep.

Objectives

1. Develop and evaluate methods to improve reproductive efficiency.
   
2. Develop strategies to improve efficiency of lean lamb growth and meat quality.
   
3. Evaluate genetic resources, nutrient requirements and production systems for lamb, wool and milk production.
   
4. Develop profitable and sustainable production systems that address grazing strategies for animal health and well-being, and for ecosystem health, biological control of invasive plants and wildfire mitigation.
   

Methods

OBJECTIVE 1

Objective 1.1: Defining the plane of nutrition to optimize flushing responses.  The goal is to optimize flushing according to season, genotype and production system. Genotypes will be prolific hair and wool breeds (e.g., Katahdin, Dorset x Polypay). The nutritional treatment of 1.5 and 2.0 times maintenance (n = 60 ewes/treatment for each breed or site) will occur 3 wk prior to ram introduction. Modifications may occur in subsequent years based on initial results in order to reach an optimal ovulation rate (number of embryos detected; lambs born) and most economical level of feed supplementation. Breeding will include a 14-d teaser exposure followed by fertile rams each rotated daily with a ram:ewe ratio of 1:20 for a 34-d breeding period. Body weight, body condition, and blood metabolites/hormones of ewes, and BW of lambs will be measured, pregnancy rate and embryo number at 25, 35, 50, 65, and 80 days post-breeding, and number of lambs/ewe up to 7 d post-lambing. Production systems will include annual and accelerated. [Collaborators: Michigan State University, Cornell University, ARS at MARC and Booneville]. 

Objective 1.1.1   Optimization of the male effect to improve reproductive outcomes of ewes during suboptimal breeding season.  At least 2 wool and 2 hair breeds of rams will be used during the suboptimal (April-June) breeding period. In the first study series, ewes (n=60+ per treatment) will be fed a standard flushing diet (1.6 times maintenance energy need for 3 weeks) and exposed to teaser rams of differing breeds for 14 d at a coverage level of 1 ram/20 ewes with teaser rams rotated daily among pens (20 ewes/pen).  A control group fed the same diet will be housed in a separate facility at least 500 meters away during the male stimulation period. Both groups will then be exposed to fertile rams of the same breed for a 34-d exposure period at a coverage of one ram/20 ewes with rams rotated between pens daily. Blood will be sampled biweekly for the 30-d period pre-flushing and continue to the end of the breeding period to measure plasma progesterone concentration to examine estrous cyclicity.  Mating behavior will be recorded 2 times/d to document standing heat and ram activity. Depending on the outcome, a second experiment may be performed to optimize the male stimulation effect by altering the intensity of teaser ram coverage. Pregnancy status will be determined (see Obj 1.1). [Collaborators: Michigan State University, ARS at MARC].

Objective 1.2   Male fertility optimization for artificial insemination. The goal is to optimize semen quality used for overnight shipment of liquid stored semen and on-farm artificial insemination. Standard semen collection of hair and wool rams will occur at each site. Semen will be extended with skim milk/egg yolk using commercial diluents, and chemically defined media, and the addition of antioxidants. Extended semen will be shipped overnight to USDA ARS NAGP (Fort Collins) using commercially available shipping systems for boar, stallion or dog. In vitro semen evaluation will occur upon arrival. Temperature loggers will be used to monitor storage temperature. Subsequent studies will validate these protocols to examine AI and fertility success. [Collaborators: VSU, ARS at NAGP and Booneville].

Objective 1.3:  Optimizing ewe lamb development programs for improved reproductive efficiency of flock. At least two genotypes will be examined (prolific hair and wool breeds). Ewe lambs will be bred at 7 and 11 months of age (n = 24 or more/age group per site) according to season of birth followed by lifetime production and repeated for 3 years. Ewes will be fed according to NRC (2007) to reach 70% of mature BW at 7 months of age and 85% of mature BW at 11 months of age. Breeding will be managed as outlined in Objective 1.1. Conception rate and embryo loss will be determined by ultrasound at 30, 45 and 60 d post-breeding, and from birth and weaning outcomes (lamb survival, BW) recorded. Production of these ewes will be recorded for at least 4 years. [Collaborators: MSU, NDSU, ARS at MARC and Booneville].

 

OBJECTIVE 2

Objective 2.1: Quantifying in-depth carcass characteristics of commercially harvested lambs.  The goal is to quantify carcass characteristics of lambs processed in the Intermountain west throughout the production year to ultimately reduce excessively fat lamb entering the supply chain. Two large scale lamb abattoirs (Mountain States Lamb Coop Greeley, CO; Superior Farms Denver, CO) will participate to provide a representative sampling of lamb carcass (n = 10,000) characteristics during seasonally constrained supply of May to August and seasonally current periods of January to May. Carcasses will be ribbed and sampled to quantify weights, 12th- rib fat depth, body wall thickness, loin-eye area, and USDA calculated, and image-based yield grades. Abattoir related expenses of harvesting, fabricating, and marketing will be evaluated to determine variable costs associated with these carcass characteristics. Partial budget analyses will estimate profits/losses when purchasing lambs that produce carcasses less than or greater than various weight thresholds. [Collaborators: University of Kentucky, North Dakota State University, University of Wyoming and USDA-ARS U.S. Meat Animal Research Center]

Objective 2.2: Evaluating feed efficiency indicators for use in the National Sheep Improvement Program.  The goal is to create a standard methodology to determine the most appropriate protocol/metric of feed efficiency for NSIP EBV calculation when GrowSafe or other feeding systems are used. Ewe, ram, and wether lambs will be sampled in order to optimize genetic connectedness among participating institutions and stakeholder flocks. Individual feed intake, feed conversion ratio, and RFI will be calculated and evaluated to determine their suitability for genetic evaluation. Non-genetic, fixed effects that significantly influence animal growth (e.g., production year, age, litter size, sex, etc.) for each trait will first be evaluated for incorporation into subsequent models of genetic prediction. Multiple-trait animal models will then be formed to estimate genetic and non-genetic (co)variances among traits. Tissue will also be collected on all phenotyped lambs to extract DNA for possible genomic association analyses conducted at a later date.  [Collaborators: University of Wyoming, West Virginia University and USDA-ARS U.S. Meat Animal Research Center, Texas A&M University, North Dakota State University]

Objective 2.3: Estimating variability in lamb growth performance and carcass quality due to genetic and non-genetic factors.  Market lambs generated from purebred Katahdin, Polypay and  Rambouillet flocks enrolled in NSIP and genetically linked to other flocks using common sires will be used. Ewes will be either purebred or crossbred mated to produce lambs. Crossbred lambs will originate from Suffolk, Hampshire, Texel, or other terminal ram breeds sampled from NSIP flocks. Market lambs will be “deep phenotyped” each year from birth through harvest using established and new phenotypes. A database of performance recorded lambs will be created which can be utilized to calculate NSIP EBV and across breed adjustments for traits not typically recorded on U.S. operations. Non-genetic, fixed effects that significantly influence animal growth (e.g., production year, age, litter size, sex, etc.) for each trait will be evaluated for incorporation into subsequent models of genetic prediction. Multiple-trait animal models will then be formed to estimate genetic and non-genetic (co)variances among traits. Tissue will also be collected on all phenotyped lambs to extract DNA for possible genomic association analyses conducted later. This base design will also lend well to investigations evaluating finishing diet and other non-genetic, husbandry practices on lamb pre- and post-harvest performance. [Collaborators: University of Wyoming, West Virginia University, USDA-ARS U.S. Meat Animal Research Center, USDA-ARS U.S. Sheep Experiment Station, USDA-ARS Dale Bumpers Small Farms Research Center, North Dakota State University]

 

OBJECTIVE 3

Objective 3.1: Estimation of genetic and non-genetic parameters of and between ewe productivity, gastrointestinal nematode susceptibility, and longevity. Historical and continual flock data will be used. Production traits will include number of lambs born/weaned and lamb weaning, post-weaning, and yearling weight. Health traits will be comprised of currently included (FEC) and potential new GIN indicator traits (FAMACHA©, packed cell volume). Longevity component traits will include udder health (i.e., subclinical mastitis indicators) and morphometric traits (depth, teat position) as well as incisor condition (missing/present, length, wear). Non-genetic, fixed effects that significantly influence animal productivity (e.g., production year, age, litter size, sex, etc.) for each trait will evaluated for incorporation into subsequent models of genetic prediction. Multiple-trait animal models will then be formed to estimate genetic and non-genetic (co)variances among traits. DNA from blood samples of all animals within USDA ARS flocks will be used for the identification of genomic regions associated with phenotypic variation when funding permits. [Collaborators: USDA ARS U.S. Meat Animal Research Center, USDA ARS Dale Bumpers Small Farms Research Center, USDA ARS Dubois Sheep Experiment Station, University of Kentucky and West Virginia University]

Objective 3.2: Genetic improvement of ewe fertility in out-of-season and accelerated lambing systems.  Fall annual flocks and accelerated lambing flocks (3 lambing events in 2 years) of varying breeds will be used for this objective. Ultrasound fertility status, fetal loss, and prolificacy data will be collected. Ewe and lamb body weight, ewe body condition score, and ram scrotal circumference will be recorded intermittently throughout the production year. Non-genetic, fixed effects that significantly influence fertility (e.g., production year, season, age, etc.) for each trait will be evaluated for incorporation into subsequent models of genetic prediction. Multiple-trait animal models will then be formed to estimate genetic and non-genetic (co)variances among traits to develop EBV for out-of-season/accelerated lambing potential. DNA of all animals within USDA ARS flocks will be collected for use in identification of genomic regions associated with phenotypic variation when funding permits. [Collaborators: USDA ARS U.S. Meat Animal Research Center, Dale Bumpers Small Farms Research Center, Michigan State University, Cornell University and University of Kentucky]

Objective 3.3: Development of multiple-trait selection indexes. Computer simulation will be used to develop bioeconomic models of sheep production systems to estimate the economic value of production, health, and longevity traits. Returns from the sale of commodities (market lambs, cull animals, wool, milk) and costs of production (labor, feed, veterinary care, etc.) will be obtained from national market summaries and industry experts. Bioeconomic models will be programmed using R and the economic value of GIN indicator, longevity, and production traits will be estimated by evaluating the change in ewe profitability for an independent, one-unit change in each trait. Economic values will be combined with results from Objectives 3.1 and 3.2 to develop multiple-trait selection indexes for use in specific production environments common to the U.S. sheep industry. [Collaborators: USDA ARS U.S. Meat Animal Research Center, Dale Bumpers Small Farms Research Center, University of Rhode Island].

Objective 3.4: Increase year-round sheep milk production. Accelerated lambing genetics from Michigan State University and Cornell will be combined with a range of proportions of East Friesian and Lacaune genetics in ewes tested to lamb and lactate on an accelerated schedule of three times in two years at Cornell University. Lactations will be for 122 days from the start of each lambing season in January, May, and September with synchronized breeding beginning on days in milk 97. Ewes will be milked twice daily and fed a highly digestible completely balanced pelleted diet high in fermentable fiber as well as high quality pasture or hay. Lambs will be removed from ewes 6 to 12 hr after birth and reared on the cold-milk lambar system. Individual milk volumes will be recorded and milk composition analyzed weekly, pregnancy will be determined via ultrasound. Lactation curves and reproductive rates will be obtained for each ewe and the estimated parameters analyzed for the effect of proportion of dairy breeding. [Collaborators: Michigan State University, Cornell University]

 

OBJECTIVE 4

Objective 4.1: Anthelmintic efficacy of Duddingtonia flagrans incorporated into free choice minerals.  Naturally infected lambs will be treated with 1) a control of no D. flagrans, 2) BioWorma (D. flagrans) to be fed as recommended as top dressed on a feed supplement, or 3) incorporated at a rate estimated to be the same in a trace mineral mix (n = 10/treatment). Mineral will be placed in mineral feeder every 7 d; refusals will be collected and weighed. All lambs will receive the same supplement and mineral (with/without D. flagrans). Lambs will be fed for 28 to 42 d.  Lambs will have access to pastures contaminated with parasitic nematode larvae before the experiment begins or be artificially infected daily during the study. Feces will be collected every 7 d for determination of FEC and coproculture for GIN genera (Pena et al., 2002). Integrity of association between D. flagrans and L3 will be assessed. Data will be analyzed using mixed models (SAS). Location will serve as replicate [Collaborators: USDA ARS Dale Bumpers Small Farms Research Center, University of Rhode Island]. 

Objective 4.2:  Anthelmintic efficacy of a pelleted cranberry vine (CV) supplement for the control of GIN in grazing lambs. Thirty weaned lambs grazing GIN infected pasture will be dewormed. Lambs will be stratified by FEC from exposure to infected pasture, balanced for gender and fed either 500 g of CV/d (n=10), 250 g CV/d (n=10) or 0 g CV/d (control, n=10). Lambs will continue to graze GIN contaminated pasture an additional 7 weeks. FAMACHA© anemia score, packed cell volume and weight will be determined weekly. At the end of the experiment, lambs will be sacrificed and GIN worm numbers will be determined (site dependent).  Studies will be replicated. [Collaborators: Cranberry vine pellet will be formulated by Cornell University and produced by URI.  Feeding trials and statistical analyses will be conducted at USDA ARS Dale Bumpers Small Farms Research Center and WVU will analyze samples for changes in immune function]. 

Objective 4.3: Determine Haemonchus contortus (H. contortus) vaccine efficacy using tropomyosin antigenic peptides.  Experimental groups will be as follows (n=8/group): 1) Adjuvant + antigen combination + 10,000 H. contortus L3; 2) Adjuvant alone + 10,000 H. contortus L3; 3) 10,000 H. contortus L3; and 4) Uninfected.  Serum antibody levels to the specific peptides will be determined using peptide-specific ELISAs at WVU. Antibody levels will be monitored 3, 7, 10 days after the first vaccination and after the booster. Two weeks after the booster, the sheep will be infected with 10,000 H. contortus L3 larvae. Fecal egg counts will be monitored after the infection has matured to determine vaccine efficacy. At the end of the trial, serum antibody levels and abomasal worm counts will be quantified. [Collaborators: WVU, USDA ARS Dale Bumpers Small Farms Research Center, URI; WVU will provide cooperating institutions with vaccine, adjuvant and larvae]. 

Objective 4.4: Biological control of invasive plants and wildfire mitigation. Sheep will be fed the weed (medusahead or ventenata or other) and then offered supplements or forages with a high concentration of one of the following: 1) protein,  2) highly digestible carbohydrate, or 3) a choice between 1 and 2. Weed intake will be assessed. The supplementation treatment that yields the greatest weed use by sheep will be tested in the field (grazing trials), where groups of 10 sheep will be supplemented (Treatment) or not (Control) on paddocks invaded by medusahead or ventenata, and replicated in space (n = 5). We expect that supplemented animals will gain more weight, show lower levels of wool cortisol (e.g., lower stress levels), and utilize the weed more efficiently (greater rates of weed intake). The design is a split-plot with spatial replications (random factor) nested within supplementation regimen (Treatment, Control). [Collaborators: Utah State University; University of Wyoming].

Measurement of Progress and Results

Outputs

• Collective data from multiple research sites will result in the optimization of protocols for the flushing of ewes, ewe lamb breeding and the shipment of fresh extended semen. Project collaborators will work in coordination throughout the project to collate, analyze and interpret data and prepare publications.
• The establishment of strong genetic connectedness between research locations and industry flocks will result in the development of new genetic selection tools for industry stakeholders. Lamb pre- and post-harvest data will be collected from multiple research sites. A survey and analyses of in-depth carcass measurements on lambs harvested at commercial and in-house abattoirs, along with the collection of growth and feed intake data and pedigree and genomic relationships will result in an improved understanding of the effects contributing to the variation in lamb performance. Project collaborators will work in coordination throughout the project to collate, analyze and interpret data and prepare publications.
• Data for traits not currently incorporated into the National Sheep Improvement Program (NSIP) will be collected at multiple research sites. Traits associated with sheep health, productivity, and longevity, in addition to those outlined in Objective 2, will be evaluated for their potential use in NSIP using standard genetic analyses. Computer simulations and producer surveys will be developed to estimate economic values of these and standard NSIP traits. Estimations of economic values and relationships among traits will then be combined to evaluate new EBV and multiple-trait selection indexes for stakeholder use. Collaborators, along with NSIP Board members and influential producers will work together on these outputs to collect meaningful phenotypic data and conduct analyses.
• New and improved strategies for the control of GIN parasites in sheep and identification of supplementation strategies to increase the consumption of invasive weeds by grazing sheep will be developed and broadly disseminated to sheep producers. Project collaborators will work in coordination throughout the project to collate, analyze and interpret data and prepare publications.

Outcomes or Projected Impacts

• The efficient use of limited sheep resources to address relevant industry constraints will result from the coordination of collaborative efforts among researchers and extension specialists.
• Improved reproductive efficiency of producer flocks will result from the implementation of improved management practices of effective breed resources generated by this research.
• Data collected at multiple research sites and its analysis will be achieved through collaboration among participating researchers. Results will provide stakeholders with genetic tools in the form of EBV to reduce feed costs, improve lamb quality and ultimately enterprise profitability.
• The development and use of selection indexes will enable producers to identify individuals with the highest overall expected genetic merit for multiple traits simultaneously. This will result in increased ewe productivity in out-of-season and accelerated lambing systems; it will ultimately enhance marketing opportunities by the increased availability of lamb and sheep dairy products on a year-round basis.
• Producers will realize an improvement in animal health and overall farm sustainability by utilization of improved strategies for parasite control of animals on pasture as well as the control of noxious weeds on western rangeland.

Milestones

(1): YR1 Objective 1.1 X 1.2 X 1.3 X 2.1 X 2.2 X 2.3 X 3.1 X 3.2 X 3.4 X 4.1 X 4.3 X

(2): YR2 Objective 1.1 X 1.2 X 1.3 X 2.1 X 2.2 X 2.3 X 3.1 X 3.2 X 3.4 X 4.1 X 4.2 X 4.3 X 4.4 X

(3): YR3 Objective 1.1 X 1.2 X 1.3 X 2.1 X 2.2 X 2.3 X 3.1 X 3.2 X 3.3 X 3.4 X 4.1 X 4.2 X 4.3 X 4.4 X

(4): YR4 Objective 1.1 X 1.3 X 2.1 X 2.2 X 2.3 X 3.1 X 3.2 X 3.4 X 4.1 X 4.4 X

(5): YR5 Objective 1.1 X 1.3 X 2.1 X 2.2 X 2.3 X 3.1 X 3.2 X 3.4 X 4.4 X

Projected Participation

View Appendix E: Participation

Outreach Plan

Project members have research, teaching and(or) extension appointments at colleges and land grant universities or are scientists with the Agriculture Research Service (ARS). Findings from the collaborative work of the members will generate refereed publications.  Members holding appointments as extension sheep specialists work directly with producers and producer groups throughout the U.S. Most members who hold research appointments or are ARS scientists also work directly with stakeholders to transfer research results and technology. Members with teaching appointments train the next generation of sheep producers, extension specialists and educators. Most members, regardless of appointment, regularly plan and participate in industry meetings and often serve on industry committees. Many members regularly contribute articles to industry publications. Several experiment stations hold field days, producer schools, other educational activities and host websites where information on current research projects is provided to producers. In addition, numerous members contribution and act as advisors to state sheep associations.

Organization/Governance

A nominating committee proposes a slate of officers consisting of Chair, Vice-Chair, and Secretary. Traditionally, the vice-chair becomes chair the following year and the secretary becomes vice-chair. Officers are elected from official representatives of participating stations. The committee votes to accept or reject the proposed slate of officers.  Administrative guidance will be provided by an assigned Administrative Advisor and a CSREES Representative.

Literature Cited

American Sheep Industry. 2014. The American Lamb Industry Roadmap. Available from: https://lambresourcecenter.com/wp-content/uploads/2015/09/Lamb-Industry-Roadmap-3-Jan-2014.pdf

Barone, C. D., A. M. Zajac, L. A. Manzi-Smith, A. B. Howell, J. D. Reed, C. G. Krueger, and K. H. Petersson. 2018. Anthelmintic efficacy of cranberry vine extracts on ovine Haemonchus contortus. Vet. Parasitol. 253:122–129.

Borg, R. C., D. R. Notter, and R. W. Kott. 2009. Genetic analysis of ewe stayability and its association with lamb growth and adult production. J. Anim. Sci. 87:3515–3524.

Borg, R. C., D. R. Notter, L. A. Kuehn, and R. W. Kott. 2007. Breeding objectives for Targhee sheep. J. Anim. Sci. 85:2815–2829.

Brown, M. A., and W. G. Jackson. 1995. Ewe productivity and subsequent preweaning lamb performance in St. Croix sheep bred at different times during the year. Journal of Animal Science. 73:1258–1263. doi:10.2527/1995.7351258x. Available from: http://dx.doi.org/10.2527/1995.7351258x

Burke, J. M. 2005. Lamb production of Dorper, Katahdin, and St. Croix bred in summer, winter, or spring in the southeastern United States. Sheep & Goat Research Journal. 20:51–59.

Burton, D. J., P. A. Ludden, R. H. Stobart, and B. M. Alexander. 2015. 50 years of the Wyoming ram test: How sheep have changed. J. Anim. Sci. 93:1327–1331.

Cammack, K. M., K. A. Leymaster, T. G. Jenkins, and M. K. Nielsen. 2005. Estimates of genetic parameters for feed intake, feeding behavior, and daily gain in composite ram lambs1,2. Journal of Animal Science. 83:777–785. doi:10.2527/2005.834777x. Available from: http://dx.doi.org/10.2527/2005.834777x

Casas, E., B. A. Freking, and K. A. Leymaster. 2005. Evaluation of Dorset, Finnsheep, Romanov, Texel, and Montadale breeds of sheep: V. Reproduction of F1 ewes in spring mating seasons1,2. Journal of Animal Science. 83:2743–2751. doi:10.2527/2005.83122743x. Available from: http://dx.doi.org/10.2527/2005.83122743x

Casu, S., I. Pernazza, and A. Carta. 2006. Feasibility of a linear scoring method of udder morphology for the selection scheme of Sardinian sheep. J. Dairy Sci. 89:2200–2209.

Casu, S., S. Sechi, S. L. Salaris, and A. Carta. 2010. Phenotypic and genetic relationships between udder morphology and udder health in dairy ewes. Small Rumin. Res. 88:77–83.

Chandrawathani, P., O. Jamnah, M. Adnan, P. J. Waller, M. Larsen, and A. T. Gillespie. 2004. Field studies on the biological control of nematode parasites of sheep in the tropics, using the microfungus Duddingtonia flagrans. Vet. Parasitol. 120:177–187.

Cloete, S. W. P., Z. Mpetile, and K. Dzama. 2016. Genetic parameters involving subjective FAMACHA© scores and faecal worm egg counts on two farms in the Mediterranean region of South Africa. Small Rumin. Res. 145:33–43.

Davies, K. W., and D. D. Johnson. 2008. Managing medusahead in the Intermountain West is at a critical threshold. Rangelands. Available from: https://bioone.org/journals/Rangelands/volume-30/issue-4/1551-501X(2008)30[13:MMITIW]2.0.CO;2/Managing-Medusahead-in-the-Intermountain-West-Is-at-a-Critical/10.2111/1551-501X(2008)30[13:MMITIW]2.0.CO;2.full?casa_token=uSsrQ-tpxPwAAAAA:RtGS99hEvX28ycdjPnEUy5i4MMCy5bRlx7aj1dwF1gVd7E-82_e7ueS31HWG3W2UD6epYqncdNI

Duckett, S. K., and P. S. Kuber. 2001. Genetic and nutritional effects on lamb flavor. J. Anim. Sci. 79:E249–E254.

Elmore, J. S., D. S. Mottram, M. Enser, and J. D. Wood. 2000. The effects of diet and breed on the volatile compounds of cooked lamb. Meat Sci. 55:149–159.

Faedo, M., M. Larsen, and P. J. Waller. 1997. The potential of nematophagous fungi to control the free-living stages of nematode parasites of sheep: comparison between Australian isolates of Arthrobotrys spp. and Duddingtonia flagrans. Vet. Parasitol. 72:149–155.

Fahmy, M. H. 1990. The accumulative effect of finnsheep breeding in crossbreeding schemes: ewe productivity under an accelerated lambing system. Can. J. Anim. Sci. 70:967–971.

Fontenot, M. E., J. E. Miller, M. T. Peña, M. Larsen, and A. Gillespie. 2003. Efficiency of feeding Duddingtonia flagrans chlamydospores to grazing ewes on reducing availability of parasitic nematode larvae on pasture. Vet. Parasitol. 118:203–213.

Forcada, F., and J.-A. Abecia. 2006. The effect of nutrition on the seasonality of reproduction in ewes. Reprod. Nutr. Dev. 46:355–365.

Foster, D. L., F. J. P. Ebling, and L. E. Claypool. 1988. Timing of puberty by photoperiod. Reproduction Nutrition Développement. 28:349–364. doi:10.1051/rnd:19880302. Available from: http://dx.doi.org/10.1051/rnd:19880302

Githigia, S. M., S. M. Thamsborg, M. Larsen, N. C. Kyvsgaard, and P. Nansen. 1997. The preventive effect of the fungus Duddingtonia flagrans on trichostrongyle infections of lambs on pasture. Int. J. Parasitol. 27:931–939.

Grønvold, J., J. Wolstrup, P. Nansen, and S. A. Henriksen. 1993. Nematode-trapping fungi against parasitic cattle nematodes. Parasitol. Today. 9:137–140.

Hötzel, M. J., S. W. Walkden-Brown, J. S. Fisher, and G. B. Martin. 2003. Determinants of the annual pattern of reproduction in mature male Merino and Suffolk sheep: responses to a nutritional stimulus in the breeding and non-breeding seasons. Reprod. Fertil. Dev. 15:1–9.

Howell, A. B. 2007. Bioactive compounds in cranberries and their role in prevention of urinary tract infections. Mol. Nutr. Food Res. 51:732–737.

Hulet, C. V., E. L. Wiggins, and S. K. Ercanbrack. 1969. Estrus in Range Lambs and Its Relationship to Lifetime Reproductive Performance. J. Anim. Sci. 28:246–252.

Inskeep, E., and P. Lewis. 2009. Eazi-Breed CIDR Sheep insert. Pharmacia and Upjohn Company.

Kerth, C. R., K. R. Wall, R. K. Miller, T. R. Whitney, W. C. Stewart, J. A. Boles, and T. W. Murphy. 2019. Effects of feeding juniper as a roughage on feedlot performance, carcass measurements, meat sensory attributes, and volatile aroma compounds of yearling Rambouillet wethers1,2. Journal of Animal Science. 97:2850–2864. doi:10.1093/jas/skz174. Available from: http://dx.doi.org/10.1093/jas/skz174

Kochendoerfer, N., and M. Thonney. 2018. Fermentable fiber for year-round ewe milk production. In: Cornell Nutrition Conference for Feed Manufacturers. Vol. 80. p. 81–87.

Kochendoerfer, N., and M. Thonney. 2019. Effect of Forage Inclusion in Diets on Milk Yield and Milk Components of Dairy Crossbreed Ewes Managed on an Accelerated Lambing System. In: Cornell Nutrition Conference for Feed Manufacters. Vol. 81. p. 118–124.

Larsen, M. 2000. Prospects for controlling animal parasitic nematodes by predacious micro fungi. Parasitology. 120 Suppl:S121–31.

Larsen, M., M. Faedo, P. J. Waller, and D. R. Hennessy. 1998. The potential of nematophagous fungi to control the free-living stages of nematode parasites of sheep: studies with Duddingtonia flagrans. Vet. Parasitol. 76:121–128.

Larsen, M., J. Wolstrup, S. A. Henriksen, J. Grønvold, and P. Nansen. 1992. In vivo passage through calves of nematophagous fungi selected for biocontrol of parasitic nematodes. J. Helminthol. 66:137–141.

Lee, M. A., N. G. Cullen, S. A. N. Newman, K. G. Dodds, J. C. McEwan, and G. H. Shackell. 2015. Genetic analysis and genomic selection of stayability and productive life in New Zealand ewes. J. Anim. Sci. 93:3268–3277.

Legarra, A., and E. Ugarte. 2005. Genetic parameters of udder traits, somatic cell score, and milk yield in Latxa sheep. J. Dairy Sci. 88:2238–2245.

Lewis, R. M., D. R. Notter, D. E. Hogue, and B. H. Magee. 1996. Ewe fertility in the STAR accelerated lambing system. J. Anim. Sci. 74:1511–1522.

Mateescu, R. G., and M. L. Thonney. 2010. Genetic mapping of quantitative trait loci for milk production in sheep. Anim. Genet. 41:460–466.

McLaren, A., K. Kaseja, J. Yates, S. Mucha, N. R. Lambe, and J. Conington. 2018. New mastitis phenotypes suitable for genomic selection in meat sheep and their genetic relationships with udder conformation and lamb live weights. Animal. 12:2470–2479.

Mekkawy, W., R. Roehe, R. M. Lewis, M. H. Davies, L. Bünger, G. Simm, and W. Haresign. 2009. Genetic relationship between longevity and objectively or subjectively assessed performance traits in sheep using linear censored models. J. Anim. Sci. 87:3482–3489.

Meyer, H. H., W. M. Aitken, and J. E. Smeaton. 1983. Inheritance of wear rate in the teeth of sheep. Proceedings of ... annual conference - New Zealand Society of Animal Production. 43. Available from: http://agris.fao.org/agris-search/search.do?recordID=US201302535202

Miller, H., D. Clausnitzer, and M. Borman. 1999. Medusahead. In: R. Sheley and J. Petroff, editors. Biology and Management of Noxious Rangeland Weeds. Oregon State University Press. p. 271–281.

Miller, L. R., J. S. Shiflett, D. J. Marsh, and P. Rodgers. 2016. U.S. Sheep Industry Research Development, and Education Priorities. American Sheep Industry Association, Inc.

Montes-Sánchez, J. J., H. Van Miegroet, and J. J. Villalba. 2017. Effects Energy Supplementation and Time on Use of Medusahead by Grazing Ewes and Their Lambs. Rangeland Ecol. Manage. 70:380–387.

Ngere, L., J. M. Burke, A. D. Herring, J. O. Sanders, T. M. Craig, J. A. van Wyk, and D. G. Riley. 2017. Utilization of year-round data in the estimation of genetic parameters for internal parasite resistance traits in Dorper sheep. Small Rumin. Res. 151:5–10.

Nieto, C. A. R., C. A. Rosales Nieto, M. B. Ferguson, J. R. Briegel, M. P. Hedger, G. B. Martin, and A. N. Thompson. 2019. Pre‐pubertal growth, muscle and fat accumulation in male and female sheep—Relationships with metabolic hormone concentrations, timing of puberty and reproductive outcomes. Reproduction in Domestic Animals. doi:10.1111/rda.13568. Available from: http://dx.doi.org/10.1111/rda.13568

Notter, D. R. 1992. Genetic improvement of out-of-season breeding through selection. In: Proceedings of the Out-of-Season Breeding Symposium. p. 19–20.

Notter, D. R., and J. S. Copenhaver. 1980. Performance of Finnish Landrace Crossbred Ewes under Accelerated Lambing. I. Fertility, Prolificacy and Ewe Productivity. J. Anim. Sci. 51:1033–1042.

O’Brien, D. R., and S. Wildeus. 2019. On-farm validation of a liquid semen vaginal artificial insemination protocol in hair sheep. Journal of Extension. 57:2RIB9.

Pearson, A. M., L. M. Wenham, W. A. Carse, K. McLeod, C. L. Davey, and A. H. Kirton. 1973. Observations on the Contribution of Fat and Lean to the Aroma of Cooked Beef and Lamb. Journal of Animal Science. 36:511–515. doi:10.2527/jas1973.363511x. Available from: http://dx.doi.org/10.2527/jas1973.363511x

Peña, M. T., J. E. Miller, M. E. Fontenot, A. Gillespie, and M. Larsen. 2002. Evaluation of Duddingtonia flagrans in reducing infective larvae of Haemonchus contortus in feces of sheep. Vet. Parasitol. 103:259–265.

Pethick, D. W. 2006. Eating quality of commercial meat cuts from Australian lambs and sheep. In: Proceedings-New Zealand Society of Animal Production. Vol. 66. New Zealand Society of Animal Production; 1999. p. 363.

Pleasants, A. B., J. M. Thompson, and D. W. Pethick. 2005. A model relating a function of tenderness, juiciness, flavour and overall liking to the eating quality of sheep meat. Aust. J. Exp. Agric. 45:483–489.

Posbergh, C. J., R. J. Murphy, and M. L. Thonney. 2017. Further testing of Melatonin Receptor 1a for out-of-season reproduction in the Cornell flock and allelic frequencies compared with Romney sheep. J. Anim. Sci. 95:1939–1944.

Posbergh, C. J., M. L. Thonney, and H. J. Huson. 2019. Genomic Approaches Identify Novel Gene Associations with Out of Season Lambing in Sheep. J. Hered. 110:577–586.

Prescott, J., O. Young, and L. O’Neill. 2001. The impact of variations in flavour compounds on meat acceptability: a comparison of Japanese and New Zealand consumers. Food Qual. Prefer. 12:257–264.

Purser, A. F., G. Wiener, and D. M. West. 1982. Causes of variation in dental characters of Scottish Blackface sheep in a hill flock, and relations to ewe performance. J. Agric. Sci. 99:287–294.

Riley, D. G., and J. A. Van Wyk. 2009. Genetic parameters for FAMACHA© score and related traits for host resistance/resilience and production at differing severities of worm challenge in a Merino flock in South Africa. Vet. Parasitol. 164:44–52.

Schoeman, S. J., and R. Burger. 1992. Performance of Dorper sheep under an accelerated lambing system. Small Rumin. Res. 9:265–281.

Schreurs, N. M., G. A. Lane, M. H. Tavendale, T. N. Barry, and W. C. McNabb. 2008. Pastoral flavour in meat products from ruminants fed fresh forages and its amelioration by forage condensed tannins. Anim. Feed Sci. Technol. 146:193–221.

al-Shorepy, S. A., and D. R. Notter. 1996. Genetic variation and covariation for ewe reproduction, lamb growth, and lamb scrotal circumference in a fall-lambing sheep flock. J. Anim. Sci. 74:1490–1498.

al-Shorepy, S. A., and D. R. Notter. 1997. Response to selection for fertility in a fall-lambing sheep flock. J. Anim. Sci. 75:2033–2040.

Snowder, G. D., and L. D. Van Vleck. 2003. Estimates of genetic parameters and selection strategies to improve the economic efficiency of postweaning growth in lambs1. Journal of Animal Science. 81:2704–2713. doi:10.2527/2003.81112704x. Available from: http://dx.doi.org/10.2527/2003.81112704x

Terrill, T. H., M. Larsen, O. Samples, S. Husted, J. E. Miller, R. M. Kaplan, and S. Gelaye. 2004. Capability of the nematode-trapping fungus Duddingtonia flagrans to reduce infective larvae of gastrointestinal nematodes in goat feces in the southeastern United States: dose titration and dose time interval studies. Vet. Parasitol. 120:285–296.

Ungerfeld, R., M. Forsberg, and E. Rubianes. 2004. Overview of the response of anoestrous ewes to the ram effect. Reprod. Fertil. Dev. 16:479–490.

USDA APHIS. 2014a. Sheep (2011): Part IV. Changes in health and production practices in the U.S. Sheep Industry, 1996-2011. Available from: https://www.aphis.usda.gov/animal_health/nahms/sheep/downloads/sheep11/Sheep11_dr_PartIV.pdf

USDA APHIS. 2014a. Sheep (2011): Part IV. Changes in health and production practices in the U.S. Sheep Industry, 1996-2011. Available from: https://www.aphis.usda.gov/animal_health/nahms/sheep/downloads/sheep11/Sheep11_dr_PartIV.pdf

USDA APHIS. 2014b. Lambing management practices on U.S. sheep operations, 2011. Available from: www.aphis.usda.gov/animal_health/nahms/sheep/downloads/sheep11/Sheep11_is_Lambing.pdf

USDA ERS. 2018. Livestock and Poultry Slaughter. Available from: https://www.ers.usda.gov/data-products/livestock-meat-domestic-data/livestock-meat-domestic-data/

USDA ERS. 2019. Livestock and meat international trade data. Available from: https://www.ers.usda.gov/data-products/livestock-and-meat-international-trade-data/livestock-and-meat-international-trade-data/

US Lamb Resource Center. 2018. Seasonality of the US lamb industry. Available from: https://lambresourcecenter.com/wp-content/uploads/2018/07/ALB-Seasonality-White-Paper-REVFINAL-07-11-18-1.pdf

Waghorn, T. S., D. M. Leathwick, L.-Y. Chen, and R. A. Skipp. 2003. Efficacy of the nematode-trapping fungus Duddingtonia flagrans against three species of gastro-intestinal nematodes in laboratory faecal cultures from sheep and goats. Vet. Parasitol. 118:227–234.

Waller, P. J., M. R. Knox, and M. Faedo. 2001. The potential of nematophagous fungi to control the free-living stages of nematode parasites of sheep: feeding and block studies with Duddingtonia flagrans. Vet. Parasitol. 102:321–330.

Whitney, T. R., and S. B. Smith. 2015. Substituting redberry juniper for oat hay in lamb feedlot diets: Carcass characteristics, adipose tissue fatty acid composition, and sensory panel traits. Meat Sci. 104:1–7.

Wildeus, S. 2005. Accelerated and out-of-season breeding with hair sheep. In: Hair Sheep Symposium. Petersburg, VA.

 

 

Attachments

Land Grant Participating States/Institutions

AR, CA, IA, ID, IN, KS, KY, MI, MS, MT, ND, NY, OH, OK, RI, SD, TX, UT, VA, WI, WV, WY

Non Land Grant Participating States/Institutions

ARS, Kansas State University, USDA-ARS Roman L. Hruska US Meat Animal Research Center