Location: Livestock Bio-Systems
2020 Annual Report
Objectives
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.
Approach
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
Substantial progress has been made toward all three objectives and their subobjectives. Subobjective 1A has been fully met and all data collection has been completed. Over the 2-year period, blood samples were obtained at day 7 of gestation from about 2000 mixed parity (1-4) sows from either Yorkshire or Landrace sired litters to determine plasma progesterone levels. From these initial sampled females, about 1500 sows farrowed with live born piglets and litter statistics recorded. The relationship of early gestation sow plasma progesterone levels and subsequent farrowing statistics were evaluated for the influence of sow genotype, sire genotype and parity. Under Subobjective 1B, sampling of excess bred gilts for ovulation rate and uterine capacity during late gestation has been substantially met. Changes in breeding protocol have resulted in limited production of excess pregnancy over the past two years in which only 22 litters have been evaluated to date. This is a significant reduction in the initially planned evaluation (about 75 litters); however, we will continue to sample excess bred gilts during the duration of the project plan cycle. In support of Subobjective 2A, phenotypic data on gilts that move through the feed efficiency barn continues to be collected as described. Reproductive data is being collected and records are added to the data base. Blood analysis has been on hold until we identify the most informative animals (most phenotypes) as described in the project plan and while technical difficulties were worked out on the liquid chromatography/ mass spectrometry instrument. Progress has been slowed because fewer animals than anticipated have made it to the breeding herd. Under Subobjective 2B, pubertal phenotypes continue to be collected and the data base resource continues to expand. RNA-seq libraries have been constructed from all tissues. Sequencing is complete for all tissues except ovary. Initial reports on transcriptome of major olfactory epithelium (MOE) and amygdala have been made. A post-doc was hired in mid-May and is conducting final transcriptomic analysis on MOE and amygdala. Preliminary analysis on olfactory bulb, hippocampus, medial basal hypothalamus, and anterior pituitary gland are underway with initial reports on these tissues expected over the next year. Within Subobjective 3A, delays continue with the development of feeders that will acquire the needed information. The company that is working with us has developed a second feeder prototype that is being tested in our system and it appears to be working correctly. The next step is to replace all existing feeders with new ones then data collection will begin. In support of Subobjective 3B, we have created microbiome libraries from milk and are working with collaborators for analyses. Subsequently plasma samples from post 4th parity females that have lifetime opportunity: production values are being analyzed for unique compounds and compound profiles using metabolomics.
Accomplishments
1. Breeding season alters chromatin modification enzyme expression in placenta of swine. ARS scientists at Clay Center, Nebraska, and University of Wisconsin collaborators found that placenta derived from summer breedings had greater expression of genes associated with epigenetic regulation in comparison to placenta from winter breedings. The swine industry regulates the environmental influence of summer by using climate-controlled housing, but seasonal reductions in farrowing rate and litter size still occur. Producers offset these losses by increasing their summer breeding stock 20-25% and subsequently increasing number of breedings by 15%. These data suggest seasonal differences in chromatin modification genes may occur to improve survivability of the developing fetuses under different environmental conditions. Therapeutics that improve favorable placental epigenetic pathways could offset seasonal reproductive inefficiency losses estimated at more than $600 million annually.
2. Genetic selection for overlapping reproductive traits in swine. Improving reproductive traits of sows via traditional breeding and management approaches is challenging for pork producers because reproductive traits are lowly heritable and expressed late in life. ARS scientists at Clay Center, Nebraska, in collaboration with researchers from the University of Nebraska-Lincoln, used a custom genotyping array containing functional single nucleotide polymorphisms (SNP) to determine if SNP located in genomic regions controlling age at puberty are also related to litter size and reproductive longevity of sows. They discovered several SNP that had overlapping association with all three of these reproductive traits and confirmed the genetic association of SNP with litter size in a commercial herd. Affymetrix produced the array making it commercially available to producers as the SowPro90. Three North American swine genetic companies are using SowPro90 to select for improved sow fertility.
3. Critical genes from uniform littermate embryos can facilitate improved synchronization of elongation, birthweight uniformity, and piglet survival. ARS scientists at Clay Center, Nebraska, in collaboration with scientists from the University of Nebraska-Lincoln, performed a transcriptomic study on the uniform population of embryos in the sow. They demonstrated drastic changes in transcriptomes as uniform populations transitioned through the initial stages of elongation. These changes are critically important during the initial transition of the embryo from spherical to ovoid morphologies. The information gained can be used to further elucidate mechanisms essential to the successful initiation of pig embryo elongation; thereby, identifying target pathways to improve synchronization of embryo elongation to produce birthweight uniformity. Uniform litters improves days to market thereby reducing producer costs.
4. Diet influences pubertal attainment in swine. In order to improve lifetime productivity of sows, managing replacement females (gilts), to achieve optimum body composition as they enter the breeding herd is a priority for producers, but appropriate strategies to achieve this goal are heavily debated in the swine industry. ARS scientists at Clay Center, Nebraska, conducted a study within a large commercial production system to evaluate growth and pubertal attainment in replacement gilts fed different diets during development. Scientists identified dietary lysine to energy ratios that allowed gilts to increase growth and development of body energy stores to support pubertal attainment. These results fill a critical need for commercial stakeholders by providing vital information about gilt development diets, yielding over $115 million in annual benefit to the swine industry.
5. Genotypic differences in placental development in response to intrauterine crowding. As litter size has increased in commercial swine production, there has been a consequential increase in preweaning piglet mortality as the result of greater within-litter birth weight variation. In contrast, Chinese Meishan pigs have large litter sizes with smaller, uniform piglets and reduced preweaning piglet mortality than contemporary Western pig breeds. The placenta has direct implications on uterine capacity, fetal growth, and survival as well as postnatal piglet growth and survival. To evaluate genotypic differences in placental development during late gestation following intrauterine crowding, ARS scientists at Clay Center, Nebraska, measured both gross and microscopic development of placentas from crowded Meishan or Western crossbred pregnancies. Meishan placentas had greater glandular exchange and greater uniformity of blood exchange across the placentas. These alterations in placental development of Meishan pregnancies corresponded to decreased allometric growth rate and within-litter birth weight variation compared to Western crossbred sows, providing a potential mechanism for reduced variability of fetal growth in response to intrauterine crowding.
Review Publications
Lents, C.A. 2019. Review: kisspeptin and reproduction in the pig. Animal. 13(12):2986-2999. http://doi.org/10.1017/S1751731119001666.
Walsh, S.C., Miles, J.R., Yao, L., Broeckling, C.D., Rempel, L.A., Wright-Johnson, E.C., Pannier, A.K. 2020. Metabolic compounds within the porcine uterine environment are unique to the type of conceptus present during the early stages of blastocyst elongation. Journal of Molecular Reproduction and Development. 87:174-190. https://doi.org/10.1002/mrd.23306.
Lindholm-Perry, A.K., Freetly, H.C., Oliver, W.T., Rempel, L.A., Keel, B.N. 2020. Genes associated with body weight gain and feed intake identified by meta-analysis of the mesenteric fat from crossbred beef steers. PLoS One. 15(1):e0227154. https://doi.org/10.1371/journal.pone.0227154.
Cushman, R.A., Soares, E.M., Yake, H.K., Patterson, A.L., Rosasco, S.L., Beard, J.K., Northrop, E.J., Rich, J.J., Miles, J.R., Chase, C.C., Gonda, M.G., Perry, G.A., McNeel, A.K., Summers, A.F. 2019. Brangus cows have ovarian reserve parameters more like Brahman than Angus cows. Animal Reproduction Science. 209:106170. https://doi.org/10.1016/j.anireprosci.2019.106170.
Gruhot, T.R., Rempel, L.A., White, B.R., Mote, B.E. 2020. The effect of varicocele on semen quality in boars exposed to heat stress. Translational Animal Science. 4(1):293-298. https://doi.org/10.1093/tas/txaa003.
