Brief Summary of Minutes of Annual Meeting

Members Not Attending: Robert Dailey and Eugene Felton, West Virginia, Robert Herd, Australia, Brett Hess (administrative adviser, Wyoming), Monty Kerley, Missouri, Robert Myer, Florida, Roberto Sainz, California, Thomas Welsh, Texas, Robert Wettemann, Oklahoma, Scott Whisnant, North Carolina. Guests: Holly Foster, Drovers. The annual meeting of the W1010 technical committee was held in Davis California on April 28-29, 2009. The meeting was called to order by the inaugural committee chair, Rod Hill. The group was welcomed to the University of California, Davis by Dr Mary Delaney, Chair of the Department of Animal Science. Each of the stations prepared a brief written report and presented this information to the group in attendance. In the business meeting, Dr Adele Turzillo (USDA-CSREES, National Program Leader) provided programmatic updates on personnel and the USDA Strategic Plan. Dr. Turzillo also provided insight into successful grantsmanship and funding opportunities. It was decided that the next year meeting would be held in Missouri, as for this year, preceding the Beef Improvement Federation meeting. Dr Carstens will serve as Chair in 2009-10. Dr Berger was elected to serve as Secretary. Following experiment station presentations, the committee explored avenues, mechanisms and future plans for collaborative research and joint grant submissions.

The Alabama Station reported two experiments. In the first experiment, fifty Simmental-Angus crossbred cows were bred AI to either a bull with a known low feed:gain ratio (FE = 4.8) or to a bull with an unknown feed:gain ratio. Sixteen male progeny resulted (8 low F:G; 8 unknown F:G). Half of the male progeny were left intact as bulls, while the other half was castrated. After weaning, the cattle were fed a total mixed diet (cp = 13%; tdn = 70%) in individual stalls for 84 days. Feed intake was recorded daily and cattle were weighed bi-weekly during the gain test period. At day 44 of the test period, muscle and adipose tissue samples (2 g each) were obtained between the 12th and 13th ribs. They were immediately frozen with liquid nitrogen and remained frozen until ready for elucidation of gene expression (mRNA abundance) using real-time PCR. For this portion of the experiment, the objective was to examine relationships between GE (mRNA abundance) of fatty acid synthase (FAS), PPAR ±, PPAR ³2, carnitine palmitoyl transferase (CPT-1b), leptin, uncoupling protein 2 (UCP-2), ubiquitin conjugating enzyme (E2) and polyubiquitin (PQ) genes in both skeletal muscle (SKM) and adipose tissue (AT) with FE and RFI in finishing cattle. Independent variables of bull type (low feed:gain ratio vs. unknown) and calf sex was used to evaluate ADG, total gain, feed:gain ratio and RFI. Bull type was not a significant source of variation for any trait. Bull calves gained faster (lsmeans 143.5 kg vs. 114.6 kg; P<0.05) with better feed:gain ratios (P<.05). There were no significant differences between feed intake of bulls and steers. Adipose FAS, leptin and PPAR³2 gene expression were unrelated to RFI. Skeletal muscle UCP-2 and E-2 but not CPT-1b, PPAR± and PQ gene expression were correlated with RFI (P<.05). Results indicate that adipose tissue genes for fat deposition are likely minimally related to RFI and FE, while skeletal muscle gene expression associated with mitochondrial metabolism and protein turnover are correlated with RFI. The transcriptomic signature for efficiency in beef cattle appears more related to skeletal than adipose tissue metabolism. In a second experiment, in which commercial yearling heifers (n=71, age = 402 days, initial BW = 433.2± 34.5 kg ) were placed on ad libitum feed (DM = 89%, CP = 13.7%) for either 79 (n=16), 100 (n=16), 121 (n=16), 142 (n=16) or 163 (n=7) days. Days on feed (DOF) group assignments were stratified across initial weight and height. Individual birth dates and breed composition were known. Heifers were trained to calan gates and individual daily feed intake and orts recorded. BW was recorded weekly. Thirty five days prior to harvest, half of each DOF group was fed 300 mg/hd/d of Ractopamine-HCL (RAC). Blood samples were taken via venipuncture at d 0, 14, 28, and 34 of the treatment phase. Ultrasound measurements of 12th rib fat, longissimus dorsi area (LMA) and percent intramuscular fat (IMF) were taken at d 0, 35 d prior to harvest and 1 d prior to harvest. Animals were humanely harvested and carcass data collected included: 12th rib fat thickness, USDA marbling score (USDA MS), %KPH, USDA Yield Grade, HCW, and LMA. At harvest, a 2 g sample of adipose, muscle and liver tissue was obtained from each carcass. Samples were immediately frozen in liquid nitrogen to be later evaluated for gene expression using real-time PCR for IGF-1, myostatin and glucose. Plasma samples were assayed for leptin, IGF-1, glucose, non-sterified fatty acids and insulin concentration via RIA. RFI will be calculated over the duration of the feeding period and the last 35 days prior to slaughter. RFI will be correlated with various measures of gene expression and assay concentrations found in the blood and tissue samples. The California Station reported that studies were conducted to model the cow-calf production system to allow comparison of management strategy by animal efficiency interactions. For example, this information could be used to improve genetics or to determine the appropriate management system for different genotypes, or animals with varying energetic efficiencies. Useful for this ongoing effort are our previously published analytical results of production and economic relationships between genetics, management, and beef quality. The Colorado Station reported that a facility is under construction to that features a 6 × 40 hd capacity feedlot with a 24-node GrowSafe system. The feedlot will also be carbon capture capable. The main research interest will be the genetics of efficient feed utilization, with collaborative projects in ruminant nutrition, physiology, and environmental impact. The new facility is scheduled for completion in August, 2009. We plan to begin conducting feed intake trials in the fall of 2009. The Florida Station reported two experiments. In experiment 1, steers (n = 170) were born in 2006 and 2007, progeny of a diallel mating of 33 sires and 143 dams from 6 breed groups (1 = Angus, 2 = ¾ A ¼ B, 3 = Brangus, 4 = ½ A ½ B, 5 = ¼ A ¾ B,and 6 = Brahman). Cows were synchronized with a progesterone-releasing device (CIDR®, Pfizer Animal Health) for 7 d (March), followed by an injection of PGF (5 ml of LUTALYSE® Pfizer Animal Health) artificially injection of PGF2± (5 ml of LUTALYSE®, Pfizer Animal Health), artificially inseminated twice, then placed with a natural service sire for 60 d (6 breeding groups with one sire per breed group). Calves were born in Spring and raised at the University of Florida Beef Research Unit (BRU), Gainesville, until weaning. After weaning, calves were pre-conditioned for 4 wk using concentrate (1.6 kg to 3.6 kg; 488 Pellet, Medicated Weaning Ration, Lakeland Animal Nutrition, Lakeland, Florida; and soy hull pellets), hay, pasture, and free choice mineral (UF University Special Hi-Cu Mineral, University of Florida, Animal Science Department, Gainesville). Calves were transported to the University of Florida feed intake facility (North Florida Research and Education Center, Marianna) in September. Animals were randomly allocated to 10 pens of 20 calves each in 2006, and to 14 pens of 13 to 14 calves each in 2007, by sire group (1 = A, 2 = ¾ A ¼ B, 3 = Brangus, 4 = ½ A ½ B, 5 = ¼ A ¾ B, and 6 = B) and sex (bull, heifer, and steer). The 2006 concentrate diet was composed of whole corn, soybean hulls, corn gluten feed, cottonseed hulls, and a protein, vitamin, and mineral supplement (FRM, Bainbridge, GA). The 2007 diet had greater fiber content (chopped bermudagrass instead of soybean hull pellets). The concentrate had a DM, CP, NEm and NEg of 91.2%, 17.3%, 1.7 mcal/kg DM NEm and 1.2 mcal/kg DM NEg in 2006 and 90.0%,14.1%, 1.5 mcal/kg DM NEm, and 0.9 mcal/kg DM NEg in 2007. The pre-trial adjustment period was of 21 d, and the trial period lasted 70 d. GrowSafe software recorded individual feed intake in real-time. Weights and exit velocity were taken every 2 weeks. Upon completion of the feed efficiency trial, steers were sent to a South Texas feedlot (King Ranch Feedyard, Kingsville, TX), and commercially slaughtered at approximately 14 mm of fat over the longissimus muscle (Sam Kane Beef Processors, Corpus Christy, TX). Residual feed intake was computed as actual minus expected feed intake (Koch et al., 1963; Arthur et al., 2001; Archer et al., 2007). Expected feed intake was a linear function of average daily gain and metabolic mid-weight. Average daily gain was computed as regression of weight on test days. Metabolic mid-weight was estimated mid-weight (estimated initial weight plus average daily gain times 35 d) to the power of 0.75. Temperament was measured as exit velocity (EV) from the chute (m/sec). Carcass traits measured were: hot carcass weight (HCW, kg), dressing percent (DP, %), longissimus muscle area (LMA,cm2), fat thickness between the 12th and 13th rib (FT, cm), kidney, pelvic, and heart fat (KPH,% of carcass weight), and marbling score (MS; USDA scores: 200 = traces, 300 = slight, 400 = small, 500 = modest, 600 = moderate). Meat quality traits were: Warner-Bratzler shear force (SF, kg), tenderness score (TS; 1 = extremely tough, 2 = very tough, 3 = moderately tough, 4 = slightly tough, 5 = slightly tender, 6 = moderately tender, 7 = very tender, 8 = extremely tender), juiciness (JU,1= extremely dry to 8 = extremely juicy), flavor (FL, 1 = extremely bland to 8 = extremely intense), thaw loss (TL, %; 100*(Frozen wt  Thawed wt)/Thawed wt), and cooking loss (CL, %; 100*(Thawed wt  Cooked wt)/Cooked wt). Traits were analyzed using single-trait mixed models (SAS Proc Mixed). Fixed effects were contemporary group (year-pen), RFI group (1 = high = RFI > 0.85 kg, 2 = medium = -0.85 kg d RFI d 0.85 kg, 3=low=-0.85kg; SD = 1.7 kg), age of calf, Brahman fraction of calf within RFI group, heterozygosity of calf, and mean EV. Random effects were sire and residual (zero mean, common variance, uncorrelated). Procedure GPLOT of SAS was used to graph least squares means by RFI group and breed group of calf. (Florida report truncated at 4223 characters, originally 8137 characters). The Idaho Station reports that a major study (four years) of the relationship between RFI and Maintenance Energy (ME) EPD in Red Angus sired calves began in 2008. ME EPD is an estimation of energy requirements needed to maintain / sustain animal body condition. When ME EPD is linked to feed efficiency (FE), a highly complementary research strategy results in which a new approach to improve FE is investigated. In addition, a new approach to estimating FE is being embraced by the scientific community largely because it is heritable and independent of many other production traits and is currently known by several different terms: net feed efficiency (NFE), residual feed intake (RFI), and net feed intake. The term RFI will be used throughout this document. RFI measures the variation in feed intake beyond that needed to support maintenance and growth requirements and is calculated as the difference between actual feed intake and the amount of feed an animal is expected to consume based on its body weight and average daily gain. Cattle eating less than expected for their body weight and average daily gain have a negative RFI value, equating to an improved feed efficiency. RFI is an intensely studied, well-developed, new measure of FE that is important to the future profitability and sustainability of the United States beef industry. This applied research and outreach project aims to convey results to all sectors of the beef industry - demonstrating the great potential of RFI as a management tool. We are characterizing Red Angus sires for RFI and evaluating the relationship between end-product quality, feed efficiency, and ME. Using the Red Angus breed as a model for others, together we will take an industry leadership role and show that adoption of RFI has advantages directly addressing the following goals: large savings in feed costs, enhancing economic opportunities and increasing profitability, and improving quality of life for beef producers. Furthermore, using less feed for similar production levels also means that this approach will result in reductions in waste products from beef cattle, and thus, reduce the environmental impact of beef production. RFI Cohort 1 Study: Prior to this project being funded, four Red Angus bulls with high accuracy ME EPD were selected. Following funding of the project, the research team (University of Idaho and RAAA) worked together to identify additional candidate sires. In May 2007, 120 cross-bred cows at the Nancy M. Cummings Research, Extension and Education Center (NMCREEC), Salmon, ID, were randomly selected for artificial insemination to the four sires initially chosen to generate Cohort 1 progeny. Cows and calves were managed under routine practices. At approximately 9 months of age, progeny of these sires, steers (n = 25) and heifers (n = 17), were transported from NMCREEC to the University of Idaho, Moscow, ID for evaluation of RFI via Calan gate technology (American Calan, Northwood, NH). Prior to the RFI measurement period, animals were allowed an approximate 2 wk adjustment period in which they were adapted to the diet and learned electronic gate operation. Pre- and post- study, animals were weighed on 2 consecutive days (d 0, d 1 and d 84, d 85) before the morning feeding. After initial body weight (BW) measurements and for the subsequent 84-d, animals were fed a growing ration individually using electronic gates. The animals were allowed ad libitum access to fresh feed, which was provided twice daily with orts weighed and recorded daily. During the 84-d test period, animals were weighed every 2 wk. Ultrasound measure for fat thickness (UFT) and LM area (ULMA) were taken on d 85. Hair was removed, and vegetable oil was applied between the 12th and 13th ribs in preparation for measurements of UFT and ULMA. Heifers were returned to NMCREEC upon completion of the test period. After the 84-d test period, the growing ration was modified in 4 stages to the finishing ration. At the time of report submission, steers are being fed the finishing ration until their rib fat depth reaches approximately 0.5 in. Steers will be slaughtered for carcass data collection and objective meat quality determination. (Idaho report truncated at 4240 characters, originally 7789 characters.) The Illinois Station reported three experiments. In the first experiment, approximately 400 sire-identified steers were randomly assigned to 50 Grow-Safe units. Six corn and corn-corn co-product based diets were randomly assigned to pen. To estimate diet digestibility, steers were fed in pens where feces could be collected underneath the slats. Bomb calorimetry was done on both the diets and feces to estimate digestible energy intake of each animal. Twenty-seven Angus, Simmental and Angus X Simmental sires were represented in this data set. The 400 head were harvest in three kill groups such that each kill group would average 1.2 cm of back fat. The RFI for the most efficient sire group was -1.59 Mcals of digestible energy per day, and the least efficient sire group was 2.09 Mcals of digestible energy. The correlation of RFI and digestible energy intake above maintenance was 0.873. When RFI was regressed against Mcals of digestible energy intake above maintenance, the R2 =0.75. These data are interpreted to suggest that as intake above maintenance increases, there is a decreasing efficiency of nutrient utilization. These data challenge the dogma that increasing intakes above maintenance should result in more efficient weight gain because a smaller proportion of the total intake is used for maintenance. For experiments two and three, sire-identified steers were fed high-concentrate diets and the heifer mates were fed high-forage diets. In year one five high use Angus sires were compared with approximately 20 steer and 20 heifer progeny per sire. The high-concentrate diet was based on corn and distillers grains. The high-forage diet was alfalfa-grass silage. The correlation between sire RFI on the high concentrate and high forage diets was 0.26. In year two steer and heifer progeny from 16 high-use Angus bulls were compared. The steers were fed a typical feedlot diet based on corn and corn co-products. The heifers were fed oatlage and a small amount of wet distillers to increase the crude protein. The correlation between sire RFI on the high concentrate and high forage diet was 0.05. The oatlage for the second year was poorer quality and resulted in gains of 0.7 kg per day compared to approximately 1.0 kg/day in the first year. These data suggest that caution is need in extrapolating RFI data for high concentrate diets to cattle fed high roughage diets. The Minnesota Station reported that in February 2009 they conducted the annual Minnesota Cow/Calf Days, with the theme of the program being Impacts of Cow Size. Two of the topics in the program were focused on the effect of cow size on overall beef production (DiCostanzo, 2009; McMurry, 2009). The message from both of these presentations was that cow/calf producers need to focus on producing efficient replacement females. Data were presented (McMurry, 2009) indicating that as cow size increased, offspring weaning weight as a percentage of cow size decreased. Additional data (DiCostanzo, 2009) were presented showing the economic impact of maintaining heavy cows that do not wean calves proportionally heavier to justify the added cost of their maintenance. These presentations took place at ten locations across Minnesota, with a total producer attendance of approximately 750. In addition, the proceedings and presentations from these meetings will be available to beef cattle producers in Minnesota and beyond. Producer evaluations from these meetings were quite positive, with many responses commenting on a renewed commitment among producers to moderate cow size and focus on efficient production in their cow herd. The positive responses will likely lead to a follow-up beef cow efficiency topic on the 2010 Minnesota Beef Cow/Calf Day program. The Minnesota station also reported a study to determine effect of feedstuff and feeding device (bunks, hay ring, rolled or ground and delivered on the ground) on dry matter intake of beef cows. Trials 1 and 2 in this experiment consisted of group feeding experiments to determine intake of various feedstuffs presented in different feeding devices. Trial 3 will utilize Calan gates to determine individual feed intakes of cows consuming various feedstuffs, and fits with Objective 3 of the W1010 committee. In Trial 3, 40 cows will be adapted to consume a mixed diet of hay and dry supplement for 14 days through individual Calan doors. Treatments will be arranged in a 2 x 2 factorial, with factors consisting of energy supplement source (corn grain and wet beet pulp) and forage source (alfalfa hay and alfalfa haylage). Cows will be fed for a period of 56 days to establish accurate intake patterns in response to changes in weather. Individual animal weights will be taken on day 1 and day 56. Feed intake will be recorded daily, and samples will be collected weekly to determine nutrient content of feed and feed refusals. The Nevada Station reported a study that investigates the molecular bases of feed efficiency by measuring RNA expression in skeletal muscle and liver and by recording feed intake and growth. Feed intake and body weight were measured in 30 animals, in three feeding regimes, during one week. Personnel and time limits did not allow for testing over a longer period of time. In addition, body weight has been recorded during growth. Animals were fed either grain/hay, corn/grain/hay, and corn/alfalfa. For each individual, at slaughter, samples were collected of the muscle, blood, heart, liver, spleen, lung and kidney. A bovine microarray (Affymetrix) would be used to identify sequences up and down regulated in muscle and liver. Sequences differentially expressed would be used in Real Time PCR for all individuals in order to establish the relationship between RNA expression of those sequences and feed efficiency. Feed samples from all treatment groups will be analyzed for energy content. Differences between animals in growth and feed efficiency using feed intake values expressed in metabolizable energy content and use these results in an economical analysis of the three feeding regimes will be analyzed. In addition, a model to estimate grazing ability in free-range ruminants based on the model that is used to estimate Residual Feed Intake (Rauw et al., 2006a) is under development. In extensive production systems, animals (seasonally) graze the rangelands, which reduces production costs because animals do not need to be fed. However, grazing animals are subject to recurrent periods of undernutrition during droughts and the winter in which large amounts of body tissue may be catabolized. Preliminary results on a grazing experiment in sheep in the cold Nevada desert showed that 94% of 915 ewes lost body weight during the grazing period, while pregnant animals in particular must gain weight (Rauw et al., 2006). Selection for within-species variation in grazing ability may offer the opportunity to breed for a better adaptation to poor quality rangelands, resulting in healthier animals and improved production. Grazing ability, however, is difficult to record in individual animals under free ranging conditions, since feed intake can not be accurately recorded without time consuming methods. Alternatively, grazing ability may be indirectly inferred from changes in body weight and production characteristics during the grazing period Rauw (2008). RFI is estimated as: FIi = b0 + (b1 × BWi0.75) + (b2 × BWGi) + ei, (1) where FIi = feed intake of individual i, BWi0.75 = metabolic body weight, BWGi = body weight gain, b0 = population intercept, b1 and b2 = partial regression coefficients representing maintenance requirements and feed requirements for growth, respectively, and ei = the error term, representing RFI. Rewriting this model gives: GAi = GIi - b0 - ei = (b1 × BWi0.75) + (b2 × BWGi), (2) where GAi = grazing ability of individual i, GIi = grazing intake of individual i, and other parameters are as in model (1). The amount of resources ingested is confounded with the efficiency of resources allocated, however, in a resource limiting environment, for the livestock producer it is more important if the animal has been able to ingest a sufficient amount of resources than if the animal is more or less efficient in allocating those. Since feed intakes and partial regression coefficients cannot be estimated in the field, estimates can be derived from the literature or from controlled experiments on a sub-group originating from the animal population of interest. A hatch project addressing this issue is currently being reviewed. Body weights can be estimated before and after animals are allowed to range freely on the rangelands, and metabolic body weight and body weight gain can be calculated. Preliminary results indicate that grazing ability is heritable, which would assure a significant response to selection when selected for. In the context of resource allocation, GA presents an estimate of the individual ability to graze at resource limiting rangelands and can be applied to different range species. (Nevada report truncated at 4156 characters, originally 5089 characters). The Ohio Station reported that a divergent selection experiment based on feed:gain ratios was conducted in the early 1980s using Angus beef cattle located at the Eastern Agricultural Research Station (EARS), Belle Valley, OH (Bishop et al., 1991a,b). Bulls were selected and individually fed during a 140-d postweaning performance test. At the end of the period, the 3 bulls with the highest feed:gain ratios and 3 three with the lowest feed:gain ratios were selected and randomly mated to 20 cows each. The progeny were then fed to assess postweaning and carcass performance. The purpose of the study was to compare mean responses of the 2 divergently selected lines of Angus beef cattle and to calculate heritability estimates for feed conversion and the phenotypic and genetic correlations between feed conversion and other economically important traits. The heritability estimates (0.46 for FCR adjusted for maintenance requirements; 0.26 for FCR unadjusted for maintenance) indicated that genetic variability for feed conversion existed in this beef cattle population. Bishop et al. (1991a,b) reported that progeny of the low FCR sires had greater subcutaneous fat than progeny of the high FCR sires, but no significant differences in other carcass traits were found. Phenotypic correlations indicated that the progeny with lower feed:gain ratios were fatter, gained weight at a faster rate, and yielded carcasses with higher quality grades, but less desirable yield grades. The selection criterion used in the divergent selection experiment was feed:gain ratio. The main objective of Shannon Smiths Masters thesis was to compare results of the selection experiment obtained using feed:gain ratios with those obtained using RFI. The sub-objectives were to: 1. Compare rankings of bulls based on feed:gain ratio vs. RFI; 2. Determine the phenotypic correlations of RFI with weights, gains, feed intake, feed:gain ratio, and backfat thickness of the bulls individually fed in the selection experiment. Between 1979 and 1983, 35 bull calves were randomly chosen each year from the purebred Angus herd located at EARS. The bull calves were individually fed in a 140-d postweaning performance test. Numbers of bulls completing the performance test in 1979 through 1983 were 35, 34, 35, 34, and 33, respectively. After weaning at approximately 7 mo of age, bulls were placed in a 3-sided barn where they were group fed for 1 wk. Bulls were then randomly assigned to individual feed bunks, where they were tied for 2 h each morning and 2 h each afternoon, and were allowed to adjust to the tying procedure for 1 wk. On-test weights were taken and recording of individual feed consumption began. Average on-test age and weight were 222 d and 232 kg, respectively. Weights and feed consumption were recorded once every 28 d. Weights were recorded in the morning before feeding. The final weight was calculated as the average of 2 weights taken on consecutive days after the 140-d performance test was completed. On the same day as the second off-test weight was taken, hip height and ultrasound estimates of subcutaneous fat thickness over the longissimus muscle between the 12th and 13th ribs were recorded. Each year, the 3 bulls with the highest feed:gain ratios and the 3 bulls with the lowest feed:gain ratios were selected from the individually fed bulls, and were randomly mated to approximately 20 cows each in a test herd of Angus cows also located at EARS. A different set of bulls was chosen each year; thus, the experiment was a single generation selection experiment replicated 4 times. The Beef Improvement Federation (BIF, 1986) recommends adjusting feed:gain ratios for differences in maintenance requirements, if feed consumption per unit of gain is evaluated over time-constant intervals. The adjustment was accomplished by multiplying the ratio of test group average metabolic midweight (Wi.75) to individual metabolic midweight (Wij.75) as follows: BIF-adjusted feed efficiency = (Wi.75/ Wij.75) (feed/gain), where subscript i refers to ith year of test (1979, 1980, 1981, 1982, or 1983) and subscript j refers to jth bull within the ith year. Midweights were estimated as ½ (initial weight on test + final weight off test). This procedure adjusts the feed conversion of heavier-than-average bulls downward, because the bulls would be expected to have above-average maintenance requirements and above-average metabolic weights (BIF, 1986). Feed:gain ratios of lighter-than-average bulls would be adjusted upward, because their maintenance requirements and metabolic weights would be below average. The bulls used for mating in the selection experiment were chosen based on their adjusted feed:gain ratios. (Ohio report truncated to 4744 characters, originally 14428 characters.) The Oklahoma Station reported that Angus nonlactating, spring-calving cows were used to determine variation in maintenance energy requirements (MR), to evaluate the relationships among MR and cow and calf performance, plasma concentrations of IGF-I, T4, glucose, insulin and ruminal temperature, and to describe the longissimus muscle (LM) proteome and evaluate protein abundance in cows with different MR. Cows (4 to 7 yr of age) with a BCS of 5.0 ± 0.2, and BW of 582 ± 37 kg, in the second to third trimester of gestation, were studied in groups. Cows were individually fed a complete diet in amounts to meet predicted MR (Level 1 Model, NRC 1996), and daily FI was adjusted weekly until constant BW was achieved for at least 21 d (maintenance). Cows were classified based on MR as low (> 0.5 SD less than mean, LMR), moderate (± 0.5 SD of mean, MMR) or high (> 0.5 SD more than mean, HMR) MR. Blood samples were taken at maintenance and at 2 mo post partum. Muscle biopsies were taken from LMR and HMR cows at maintenance. Proteins from LM were separated by two-dimensional, difference gel electrophoresis and abundance was quantified and compared. The greatest differences in MR between cows were 29% (n = 23), 24% (n = 32), and 25% (n = 38) in the 3 groups. Daily MR (NEm, Kcal"BW-0.75"d-1) averaged 89.2 ± 6.3, 93.0 ± 4.9, and 90.4 ± 4.6, in groups 1, 2 and 3, respectively. Postpartum BW and BCS, calves birth and weaning weights, resumption of luteal activity after calving, plasma concentrations of hormones and ruminal temperature were not influenced by MR of the cows. However, MR was negatively correlated with concentrations of IGF-I in plasma (r = -0.38; P = 0.05) and tended to be positively correlated with T4 in plasma (r = 0.31; P = 0.12) at 2 mo post partum. A total of 103 proteins were isolated from the LM, and 52 gene products were identified, of which many (33%) participated in metabolism. Protein abundance tended (P = 0.11) to be greater in HMR cows for cofilin-2. Greater abundance of cofilin-2 in HMR cows may have application as a biomarker for MR. . Productive cows that require less feed for maintenance will improve efficiency of production and enhance the sustainability of the environment. The Texas Station reported on results from four experiments. In the first experiment (Lancaster et al., 2008), Angus bulls and heifers from the Ohio Station that were divergently selected for serum insulin-like growth factor-I (IGF-I) concentration were used to evaluate the effects of IGF-I selection line on feed efficiency traits in 2 studies. In study 1, bulls (low line n = 9; high line n = 8) and heifers (low line n = 9; high line n = 13) were fed a roughage-based diet (ME = 1.95 Mcal/kg DM), and in study 2, bulls (low line n = 15; high line n = 12) and heifers (low line n = 9; high line n = 20) were fed a grain-based diet (ME = 2.85 Mcal/kg DM). Blood samples were collected at weaning and at the start and end of each study and serum IGF-I concentration determined. RFI was calculated, within study, as the residual from the linear regression of DMI on mid-test BW0.75 (MBW), ADG, gender, gender by MBW and gender by ADG. In study 1, calves from the low IGF-I selection line had similar ADG compared to calves from the high IGF-I selection line. DMI and feed conversion ratio (FCR) were also similar between IGF-I selection lines, however, calves from the low IGF-I line tended (P < 0.10) to have lower RFI than calves from the high IGF-I line (-0.26 vs. 0.24 ± 0.31 kg/d). In study 2, IGF-I selection line had no influence on performance or feed efficiency traits. However, there was a tendency (P = 0.15) for an IGF-I line by gender interaction for RFI. Bulls from the low IGF-I line had numerically lower RFI than those from the high IGF-I line, whereas, in heifers IGF-I line had no effect on RFI. In studies 1 and 2, weaning and initial IGF-I concentrations were not correlated with either FCR or RFI. However, regression analysis revealed a gender by IGF-I concentration interaction for initial IGF-I concentration in study 1 and weaning IGF-I concentration in study 2, such that the regression coefficient was positive for bulls and negative for heifers. These data suggest that genetic selection for postweaning serum IGF-I concentration had minimal effect on RFI in beef cattle. In the second experiment (Lancaster et al., 2009a), data from 341 Angus bulls was used to characterize feed efficiency traits and to examine phenotypic correlations with feeding behavior and carcass ultrasound traits. Individual DMI and feeding behavior traits were measured in bulls fed a corn silage-based diet (ME = 2.77 Mcal/kg DM) using a GrowSafe feeding system. Ultrasound measures of carcass 12-13th rib fat thickness (BF) and longissimus muscle area (LMA) were obtained at the start and end of each of 4 trials. Residual feed intake (RFIp) was computed from linear regression of DMI on ADG and mid-test BW0.75 (MBW) with trial, trial by ADG and trial by MBW as random effects. Overall ADG, DMI and RFIp were 1.44 (SD = 0.29), 9.46 (SD = 1.31), and 0.00 (SD = 0.78) kg/d, respectively. Stepwise regression analysis revealed that inclusion of gain in BF and LMA in the base model increased R2 (0.76 vs. 0.78), and accounted for 9% of the variation in DMI not explained by MBW and ADG (RFIp). RFIp and carcass-adjusted RFI (RFIc) were moderately correlated with DMI (0.60 and 0.55) and FCR (0.49 and 0.45), and strongly correlated with partial efficiency of growth (PEG; -0.84 and -0.78), but not with ADG or MBW. Gain in BF was weakly correlated with RFIp (0.30), FCR (-0.15), and PEG (-0.11), but not RFIc. The Spearman rank correlation between RFIp and RFIc was high (0.91). Meal duration (0.41), head-down duration (0.38), and meal frequency (0.26) were correlated with RFIp, and accounted for 35% of the variation in DMI not explained by carcass-adjusted RFIc. These results suggest that adjusting RFI for carcass composition will facilitate selection to reduce feed intake in cattle without affecting rate or composition of gain. In the third experiment (Lancaster et al., 2009b; accepted), 468 Brangus heifers were used in 4 postweaning trials to characterize RFI and to estimate phenotypic and genetic correlations with performance and ultrasound carcass traits. The pedigree file from Camp Cooley Ranch included 31,215 animals. Heifers were individually fed a roughage-based diet (ME = 1.98 Mcal/kg DM) using Calan gate feeders for 70 d. Heifer BW were recorded weekly and ultrasound measures of 12-13th rib fat thickness (BF) and longissimus muscle area (LMA) obtained at d 0 and 70. (Texas report truncated at 4411 characters, originally 7430 characters.)

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