Introduction:  Swine production is globally distributed. The U.S. is the world's third-largest swine producing country behind China and the E.U. The U.S. has been the world’s largest or 2nd largest exporter of pork and pork products, with exports being projected to be 23.5% of domestic commercial pork production (USDA, 2022a). Currently, U.S. pork production operations are heavily concentrated in the Midwest and eastern North Carolina. In 2021, an estimated 180 million hogs were slaughtered in the U.S. for an estimated gross on-farm value of $18.0 billion (USDA, 2022b). The average inventory as of September 1, 2022 was 73.8 million swine, of which 6.15 million were sows (USDA, 2022c). Swine production is driven by the fact that pork continues to be one of the major high-quality sources of protein in human diets and, because of its flavor, pork is the meat of choice worldwide with a U.S. average annual per capita consumption of 23.4 kg (USDA, 2022a).

Need as indicated by the stakeholders: Swine enterprises constitute a major source of on-farm income in the Southern Region of the U.S., and pork production in the Southern Region represents a significant portion of the U.S. pork production, especially sow production. The most rapidly growing component of swine production in the Southern Region has been in sow farms producing feeder pigs that are shipped to the Midwest for feeding to market weight. This trend is attributed to favorable environmental conditions, the availability of labor, and interest in contract swine production in the Southern Region, and to an availability of feedstuffs in the Midwest.

A primary factor affecting the profitability of swine production is sow productivity. Optimum nutrition of the sow is essential to maximize sow productivity and longevity. An ideal nutrition program should provide adequate nutrients to maximize sow productivity and health while minimizing the environmental footprint and feed costs. The continuing trend to increased litter size and intensive production schedules places biological demands on the sow that make high performance difficult to obtain and maintain without compromising sow health and wellbeing. An increase in the number of pigs marketed/sow/year through improved sow nutrition would result in increased profitability by allocating fixed sow costs over more pigs. However, increased productivity can decrease longevity in the herd without proper nutrition. Studies indicate that a sow must complete at least 3 parities before reaching a positive net present value (the point when she has covered purchase price and feed costs; Stalder et al., 2000, 2003).

The research committee of the National Pork Board (NPB) has identified improvements in sow nutrition as an area needing further research. The current S-1081 committee meets yearly with members of the American Feed Industry Association, the NPB, and representatives from large feed companies to survey their assessment of research priorities. The specific research objectives that we have chosen result directly from those meetings. All segments of the industry recognize sow productivity and nutrition as extremely important factors affecting profitability in swine production systems. In fact, sow longevity is one of the key research areas identified by the NPB for the use of the commodity checkoff monies that are appropriated for research. Although progress has been made in sow nutrition in the last 30 years, there is still a dearth of information relative to specific nutrient requirements of the very prolific and high milk-producing sows used today. Further research is greatly needed to accurately define the levels of various nutrients necessary for optimizing reproduction and lactation while minimizing nutrient excretion.

Importance of the work: It is extremely important to conduct research that provides solutions to potential sow nutrition and production problems and the impact that concentrated production systems have on the environment. Societal perspectives and governmental regulations place extreme pressures on pork production systems. Solutions to these issues must be provided so that swine production, a critically important component of agricultural productivity, will remain and continue to be an economically viable opportunity for our work force.

Technical feasibility of the research: The original Southern Multi-State Research Group (S-145) and the current group (S-1081; previously S-288, S-1012, S-1044, and S-1061) have made significant contributions in obtaining new knowledge and creating a better understanding of the nutritional needs of sows to improve reproductive efficiency. This Technical Committee has used the approach of: 1) defining high priority research areas in direct collaboration with stakeholders, 2) developing common protocols that are followed by all participating stations [with certain aspects rigidly followed by all participants and other aspects having flexibility for individual stations], 3) pooling the data, 4) drawing conclusions, 5) publishing the pooled results as abstracts at professional meetings and in peer-reviewed scientific journals, and 6) dissemination of research results through extension programming, trade magazines, and direct producer contact. Since its inception through 2022, the Committee has published 27 refereed publications, 2 conference proceedings, 43 abstracts, and 1 extension publication. These publications are the direct result of the collaborative research efforts of the Southern Multi-State Research Group. Also, in collaboration with the NCCC-42 Committee, the Committee has published two books and four book chapters. The first book published was entitled "Swine Nutrition" (now in its second hardcopy edition) and the second book published was entitled “Sustainable Swine Nutrition” (now in its second hardcopy edition and also available as an e-book). Committee members have been asked to speak at a number of producer and industry conferences to discuss research results. The S-1012 Committee was nominated by the Southern Region Department Heads for the NASULGC award for regional research. Over the last 20 years, participants in the Committee have clearly demonstrated that they can successfully collaborate in multi-state research. In addition, we meet annually with the NCCC-42 Committee, which is an informational exchange group working on swine nutrition. We have opened our objectives to their participation as well as participation by other institutions.

Justification for a multi-state approach: Sow research is well suited to a regional approach for three major reasons. First, in reproductive studies, large numbers of animals are required to generate meaningful data; individual experiment stations often do not have sufficient sow numbers for sow research. Progress in sow nutrition and management research is hampered by the large variation among sows in economically important reproductive traits (Aaron and Hays, 1991). In a summary of 7,925 farrowings in five herds, the coefficients of variation were 26-33% for total and live pigs farrowed and 36% for pigs weaned (Aaron and Hays, 2004). In contrast, the coefficients of variation for growth rate and feed efficiency were 5-8 and 4-7%, respectively, for pens of growing and finishing pigs. The number of replications needed to detect a 10% difference in litter size at birth and at weaning, at an 80% success rate and a 5% probability level, is 99 and 193 sows per treatment, respectively. Thus, it is difficult for individual experiment stations to generate the number of observations needed to reach statistically significant conclusions. Second, pooled results from several experiments conducted with a common protocol but under different environments provide valuable information from which broad inferences can be drawn, and more robust recommendations can be made. A third advantage of a multi-state approach is that the combined experience and expertise of several swine nutritionists can be focused on the most high-priority objectives. Additionally, a planned annual meeting provides opportunities to discuss new and old research findings.

Goals and impacts of the current research: The primary goal of this proposed project is to improve the reproductive performance of sows while increasing their retention in the herd, enhancing offspring robustness, and minimizing sow nutrient excretion. This research will include studies to evaluate sow lactation histidine requirements, enhancing lactation feed intake, and biological indicators of sow nutritional status, to both improve the reproductive performance of sows and improve the economic return to swine producers. Histidine is an amino acid that may become limiting to milk production when aggressive amino acid supplementation is used to take advantage of increasingly affordable synthetic amino acids and to reduce nitrogen excretion (done to minimize environmental impact). Low sow feed intake is a primary factor involved in low weaning weights of piglets and excessive body weight loss of the sow during lactation, resulting in greater time in returning to estrus. Finally, if biomarkers of nutritional status can be identified that are associated with the range of sow performance and sow wellbeing, they could potentially be used as early intervention indicators to more closely meet changing nutrient demands, limit excess protein excretion, and reduce diet production costs; however, there is currently too little data on this to begin its use for optimizing sow production and wellbeing. As sow health and productivity is increased by success in any of these objectives, there is potential for improvement in enterprise profitability. The results will also demonstrate responsiveness to societally-important issues of waste management and the environment as well as concerns about animal wellbeing in animal production.