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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Livestock Bio-Systems » Research » Research Project #433074

Research Project: Improving Lifetime Productivity in Swine

Location: Livestock Bio-Systems

2022 Annual Report

Objective 1: Improve swine production by identifying factors contributing to prenatal piglet development and survival and postnatal preweaning mortality. Subobjective 1.A: Improve conceptus, postnatal, and preweaning survival by determining early pregnancy factors contributing to variation in fetal and postnatal development. Subobjective 1.B: Increase piglet production by discovering fetal and postnatal development features that are influenced by uterine capacity. Subobjective 1.C: Determine the influence of placental membrane transporters on placental and fetal development. Objective 2: Increase productivity and longevity of replacement gilts by identifying and defining physiological and environmental factors underlying developmental and reproductive processes. Subobjective 2.A: Improve strategies for selecting gilts by defining environmental, physiological, and metabolic factors responsible for variation in growth and reproductive efficiency. Subobjective 2.B: Reduce failure of gilt retention through discovery of gene pathways and their interaction with physiological and environmental factors affecting the phenotypic expression of pubertal traits. Objective 3: Enhance sow performance and retention within the breeding herd by identifying physiological and environmental features at critical periods throughout life that contribute to production and longevity. Subobjective 3.A: Identify behavioral and environmental factors during gestation, lactation, or post-weaning periods to develop feeding strategies that improve sow reproductive performance and longevity. Subobjective 3.B: Discover factors (microbiome profiles, metabolites, transcripts, proteins, and/or genes) within tissues or biofluids from female breeding stock for use in genomic, metabolomic, or microbiome studies to improve reproductive efficiency, piglet production, and sow longevity.

Maximizing lifetime productivity of swine is essential to meet the ARS Grand Challenge of a 20% increase in production and a 20% reduction in environmental impact by 2025 and is a high priority research initiative of the pork industry. Lifetime productivity of swine is an extremely complex trait and our understanding of the biological mechanisms that underlie the trait or its component traits is limited. Increasing our knowledge and basic understanding of development, growth, and maintenance at all levels of swine production will impact lifetime productivity. The overarching goal is to discover physiological, metabolic, and environmental factors affecting fetal survival, piglet growth, reproductive development, and sow productivity and longevity. This will be accomplished by combining transcriptomics, metabolomics, microbiomics and other molecular biology techniques with genetic and physiological studies at the farm level. Our first objective will focus on conceptus through neonate to produce more consistent-sized, healthy piglets, subsequently reducing pre-weaning mortality and improving growth rates. Secondly, we will identify factors that contribute to young females that have greater success entering and staying in the breeding herd. Our final objective will investigate environmental and energy dynamics of mature females relating these to production and longevity. The tools and strategies developed from this project will be used to improve pork production efficiency. Maximizing lifetime productivity of swine will enhance the welfare and well-being by minimizing fetal and neonatal death, and reducing unnecessary culling of gilts and sows. Application of these results will increase the economic competitiveness of U.S. pork producers.

Progress Report
This is the final report for project 3040-31000-095-000D. Significant accomplishments have been achieved to address the three primary objectives of prenatal development and survival and postnatal preweaning survivability, productivity and longevity of gilts, and sow performance and retention. Over the course of the previous five years, this research has reported 25 accomplishments and produced 33 referred publications. Substantial progress has been made toward all three objectives since the inception of the 3040-31000-095-000D project in fiscal year (FY) 2018. Within Objective 1, novel findings have been reported that support the interactions of the early uterine environment and stage of the embryo to generate uniform litter sizes at farrowing. Metabolic profiles of uterine flushings were unique as porcine conceptuses transitioned between spherical, ovoid, and tubular stages. Transcription of genes from spherical, ovoid, or tubular conceptuses were dramatically different and highlighted putative pathways that could be altered to improve embryo uniformity and signaling in the uterus. Chinese Meishan pigs produce large litters with small uniform piglets in contrast to White Composite sows with varying litter uniformity, contributing to pre-weaning morbidity and mortality. Investigations of placental development between the Chinese Meishan and White Composite lineage indicated advanced glandular development and a greater uniformity of blood exchange in placentas derived from Meishan dams. These data support the efforts investigating the early conceptus uniformity, which contributes to placental development and function and within-litter birthweight variation. Analyses of progesterone from early pregnancy females has been completed in support of Objective 1. Embryo elongation and membrane vesicle exosome work continues in collaboration with university partners under an existing and a newly funded Agriculture and Food Research Initiative/ National Institute of Food and Agriculture proposal. Objective 2 was supported by multiple projects contributing to the understanding of pubertal development in gilts and stayability of sows in the breeding herd. Reproductive development and function of gilts can be influenced by diet from as early as birth through entrance into the breeding herd. Scientists discovered that over 1,100 genes in the pregnant uterus were expressed differently in gilts that had consumed adequate amounts of colostrum as baby piglets compared with those that did not. Whereas energy balance in developing gilts affected the release of the reproductive hormone, luteinizing hormone, and changed the expression of several hypothalamic and anterior pituitary genes associated with reproductive hormones. Additionally, lysine and energy ratios in gilt development diets can be reduced without adversely affecting pig production, but further studies are needed to determine if reductions in growth rate might have negative consequences for sow longevity. Genetic polymorphisms with overlapping associations for puberty, litter size, and sow lifetime productivity were evaluated and are now commercially available for improved genetic selection. Within Objective 2, genetic analyses and differential gene expression of pubertal traits and sow longevity are actively being conducted and supported by post-doctoral efforts. In support of Objective 3, studies were conducted to bolster the understanding of physiological events and environmental factors that impact sow longevity in the breeding herd. Young naïve dams have a delayed recovery of muscle and adipose tissue following weaning of their first litter. ARS researchers at Clay Center, Nebraska, determined that these dams also had an altered metabolic profile that supported stimulation of feed intake and muscle accretion while delaying reproductive function. Modern swine facilities manage environmental fluctuation throughout the year yet decreases in female stayability and piglet production occur seasonally. Investigations addressing genetic expression in placenta from summer-derived or winter-derived pregnancies suggested an epigenetic alteration due to season of breeding. These data provide evidence that epigenetic-modifying therapeutics may be employed to improve seasonal reduction in pregnancy rate, farrowing rate, and litter size. Breeding females are often culled from the herd due to reduced litter production, however the male contribution, sperm, may be impacting the outcome of the female. Investigations into the impact of season of semen collection on the placental and fetal liver gene expression was altered and less favorable for semen collected during warm temperatures. Boars used for semen collection must meet quality standards for commercial usage. However, research from ARS in collaboration with university counterparts identified boars with a genetically heritable condition known as varicocele, distended and dilated blood vessels in the pampiniform plexus that supply blood to the testes. Under homeostatic environmental conditions, these boars appeared to have normal morphology and fertility, however upon a heat stress event, a measurable depreciation in semen quality occurred. Subtle seasonal perturbations in semen quality from boars that were otherwise deemed acceptable may contribute to female cull rates due to reduced fertility and production. We have begun collecting feed behavior data and environmental condition data within the gestation unit in support of Objective 3. Gestation and farrowing data will be collated and used to determine if a relationship exists with farrowing events such as litter size, piglet morbidity and mortality, piglet growth, and sow stayability.

1. Females that fail to express sexual interest have altered expression of genes in the brain. Approximately 12% of gilts selected to enter the swine breeding herd fail to produce a litter because they do not display sexual behavior and are not receptive to mating. To better understand how to solve this problem, ARS scientists at Clay Center, Nebraska, studied how genes in two regions of the brain involved in sexual behavior differed in gilts that do, or do not, display sexual interest. Several differentially expressed genes among gilts that fail to display sexual behavior were involved with nervous system function and known behavioral disorders. Potential options for producers would be to develop gene expression screening methods for young females to determine the likelihood of successfully displaying sexual behavior, thereby improving reproductive efficiency in the breeding herd.

2. A sow’s parity and lactation performance do not influence piglet growth and maturation. Many producers are reluctant to retain breeding gilts (young females) from first-parity sows that are less mature. The industry dogma is that gilts from first parity sows tend to grow more slowly and have delayed sexual maturation. Consequently, many producers do not select replacement females produced by these young sows, which reduces the number of candidate breeding gilts available in the herd. ARS scientists at Clay Center, Nebraska, investigated the production and performance of piglets reared by first-parity through fourth-parity sows and their subsequent growth and reproductive performance. Piglets raised by first-parity sows were smaller at birth and weaning but grew to similar weight and body composition later in life as those raised by older, more mature sows. In addition, gilts raised by first-parity sows had similar or better sexual maturity than those raised by mature sows. These findings indicate that gilts selected for breeding from first-parity sows will not have reduced growth to maturity or reduced reproduction efficiency when compared to breeding gilts produced from older sows.

3. Dynamic gene expression changes occur during early pig embryo development. ARS scientists at Clay Center, Nebraska, in collaboration with scientists from the University of Nebraska-Lincoln, performed a gene expression study on early embryos in the sow to better understand how embryos grow and develop. A high number of gene expression differences were observed during the initial development of the embryo. These observations reiterate the importance of gene regulation during this initial phase of embryo development. Specifically, changes in genes and associated pathways involved in hormone signaling in the embryos were actively different between embryos. The information gained from this study can be used to further elucidate mechanisms essential to the successful development of pig embryos leading to more uniform litters of piglets, which will improve production efficiencies for pork producers.

Review Publications
Walsh, S.C., Miles, J.R., Keel, B.N., Rempel, L.A., Wright-Johnson, E.C., Lindholm-Perry, A.K., Oliver, W.T., Pannier, A.K. 2022. Global analysis of differential gene expression within the porcine conceptus transcriptome as it transitions through spherical, ovoid, and tubular morphologies during the initiation of elongation. Molecular Reproduction and Development. Article 23553.
Rempel, L.A., Keel, B.N., Oliver, W.T., Wells, J.E., Lents, C.A., Nonneman, D.J., Rohrer, G.A. 2022. Dam parity structure and body condition during lactation influence piglet growth and gilt sexual maturation through pre-finishing. Journal of Animal Science. 100(4):1-9. Article skac031.
Wijesena, H.R., Nonneman, D.J., Keel, B.N., Lents, C.A. 2022. Gene expression in the amygdala and hippocampus of cyclic and acyclic gilts. Journal of Animal Science. Article skab372.
Harlow, K., Renwick, A.N., Shuping, S.L., Sommer, J.R., Lents, C.A., Knauer, M.T., Nestor, C.C. 2021. Evidence that pubertal status impacts kisspeptin/neurokinin B/dynorphin neurons in the gilt. Biology of Reproduction. 105(6):1533-1544.
Lindholm-Perry, A.K., Kuehn, L.A., Wells, J., Rempel, L.A., Chitko-McKown, C.G., Keel, B.N., Oliver, W.T. 2021. Hematology parameters as potential indicators of feed efficiency in pigs. Translational Animal Science. 5(4). Article txab219.
Miles, J.R., Walsh, S.C., Rempel, L.A., Pannier, A.K. 2022. Mechanisms regulating the initiation of porcine conceptus elongation. Molecular Reproduction and Development. Article 23623.
Nonneman, D.J., Lents, C.A. 2022. Functional genomics of reproduction in pigs: Are we there yet?. Molecular Reproduction and Development. 90(7): 436-444.
Snider, A.P., Crouse, M.S., Rosasco, S.L., Epperson, K.M., Northrop-Albrecht, E.J., Rich, J.J., Chase, C.C. Jr., Miles, J.R., Perry, G.A., Summers, A.F., Cushman, R.A. 2022. Greater numbers of antral follicles in the ovary are associated with increased concentrations of glucose in uterine luminal fluid of beef heifers. Animal Reproduction Science. 239. Article 106968.