Location: Reproduction Research2013 Annual Report
1a. Objectives (from AD-416):
1) Determine prenatal, postnatal and prepubertal factors influencing puberty onset and develop strategies to reduce puberty failure. - Sub-objective 1.A. Establish the effects of neonatal litter size on development of the reproductive tract of gilts. - Sub-objective 1.B. Establish the long-term effects of the size of neonatal litter in which the gilt is suckled on feeding behavior during prepubertal development and subsequent lactation performance as sows. - Sub-objective 1.C. Determine how prenatal development influences the onset of puberty. 2) Assess placental, fetal, maternal blood, genetic, epigenetic and postnatal factors contributing to conceptus loss and piglet preweaning mortality. - Sub-objective 2.A. Determine the genetic basis for uterine capacity, stillbirth and preweaning mortality. - Sub-objective 2.B. Assess how gene imprinting influences placental, fetal and postnatal development. - Sub-objective 2.C. Physiological mechanisms governing fetal blood flow distribution. - Sub-objective 2.D. Determine the influence of energy dynamics during prenatal and neonatal development on piglet survivability. - Sub-objective 2.E. Develop applied techniques to improve litter size and preweaning survival. 3) Evaluate the contribution of energetic demands during pre-, peri- and post-parturition on reproductive parameters and retention of sows in the breeding herd. - Sub-objective 3.A. Evaluate phenotypic factors and identified genetic regions that influence sow longevity. - Sub-objective 3.B. Investigate the influence of sow feed efficiency, metabolic activity and lactation performance during and after lactation on piglet survival, piglet growth and post-weaning reproduction performance of sows.
1b. Approach (from AD-416):
Sows must remain in the breeding herd for 3 to 4 parities to produce enough weaned piglets to be profitable. This plan describes experiments that focus on gilt development, the number of piglets weaned, and retention of sows in the breeding herd. These three factors have been identified by the National Pork Board as high priority research topics, because they each affect sow lifetime productivity. Genomic approaches will be used to develop genetic markers to improve these traits, taking advantage of animal numbers and critical expertise in genomics at USMARC. In addition, experiments focused on gilt development will elucidate factors contributing to the effects of litter birth environment of gilts before weaning on puberty, bone development and retention of sows in the herd. Factors contributing to litter size such as genetic imprinting, control of fetal blood flow, and arginine supplementation during pregnancy will be investigated. Factors contributing to preweaning survival such as development of energy stores within the fetus and neonate, the role of lactation and neonatal activity, and the effect of timing of farrowing induction will be investigated. Experiments focused on retention of sows in the breeding herd will investigate metabolic activity of the sow, with special attention to the demands and consequences of lactation on sow postweaning return to estrus. These experiments are enhanced by the expertise in these areas of the personnel assigned to the project. We expect to provide the swine industry with information, management strategies and genetic markers that will improve sow lifetime productivity.
3. Progress Report:
Subobjective 1A. The experiment has been started. The first replicate of the first year has been initiated and the tissue collections from this replicate will be completed by the end of July. Laboratory analysis of the ovarian and uterus tissues will commence immediately following July. The second replicate will begin in September. Subobjective 2A. We were successful in developing Sodium metabisulfite techniques for sequencing the region of the FGF2 gene. Bisulfite sequencing of this region indicated that the GCG repeat length did not differ between Meishans and BX pigs. Much of the cloning and sequencing work proposed in the project has now been superseded by high throughput sequencing of the founder animals from the BX population at U.S. Meat Animal Research Center, Clay Center, Nebraska. Sequencing identified hundreds of SNPs within the FGF2, Thromboxane A2 receptor and SLIT2 genes, and we are currently developing genotyping assays. Of the SNPs discovered in SLIT2, one is predicted to alter an amino acid in the C terminal end of the protein. The other is a frameshift that is predicted to truncate the protein. Subobjective 2B. Breed differences in placental tissue gene expression between Meishan and white composite pregnancies were evaluated using microarrays. Among the breed-specific differences detected were those for several imprinted genes. Three paternally expressed genes (NAP1L5, SNORD107, SNRPN) and the maternally expressed PHLDA2 showed significantly higher expression in Meishan placenta. In white composite placenta, significantly higher expression of paternally expressed IGF2, INPP5F, MEST, PEG10, PEG3 and maternally expressed IGF2R, MEG3, and OSBPL1A were observed. Profiles of imprinted gene expression in placenta along with X-chromosome linked genes, lipid, and cholesterol metabolism differences formed the basis for an improved model of placental function. Subobjective 2D: An initial analysis of the expression of the key enzymes in the glycogen metabolism in the liver and muscle has been made. Analysis of these genes for SNPs has been delayed by other work and will take place in 2014. The litters that will be used for collecting neonatal tissues for further analyses of glycolytic enzymes and activity levels are scheduled to farrow in April and May 2014. Activity of second parity sows and their offspring will be evaluated in September and October 2014. Subobjective 3A. The first year of data collection was completed in which dams were measured following farrowing and again at weaning for body weight, backfat thickness, and loin eye area. A plasma sample was acquired for future metabolomics work. Post-weaning reproductive performance was also observed. Our results so far provide evidence to indicate that body weight, backfat thickness, and loin eye area from fully mature animals reflect unique genetic regions of interest compared to genetic regions from growing and finishing animals. Results further suggest that genetic regions overlap between backfat thickness and loin eye area.
1. Identification of DNA markers predictive of puberty in gilts. Approximately one-third of female pigs selected for breeding (gilts) are culled due to failure to reach puberty and become pregnant. ARS researchers at Clay Center, Nebraska, discovered 12 genetic markers that were associated with failure of gilts to reach puberty. Use of these genetic markers will allow selection of gilts that will reach puberty and become pregnant, thereby increasing reproductive efficiency and reducing the expense of pork production.
2. Identification of physiological mechanisms and genes controlling feed intake, reproduction and growth in swine. Feed costs account for 72% of the variable cost of pork production. ARS researchers at Clay Center, Nebraska, discovered that the protein nesfatin-1 controls appetite in the pig and found that genetic markers in the nesfatin-1 gene were significantly correlated with body weight at puberty. These new genetic markers will be used in marker assisted selection to improve feed efficiency and reduce the expense of pork production.
3. Analysis of gene expression in pig placental epithelial cells. The placenta is responsible for the transport of all nutrients needed for the growth and development of the pig fetus during pregnancy. Increased placental function could reduce the number of low birth weight piglets, thereby improving preweaning survival and piglet growth potential. Placental epithelial cells make up the surface that interacts with the mother, and two broad factors contribute to placental nutrient transport: 1) the epithelial cell layer becomes highly folded during pregnancy to increase the interacting surface area and 2) the cells produce specific proteins that facilitate the transport of a variety of nutrients. To gain insight into what controls folding of the epithelial cell layer and to identify all the nutrient transport proteins, ARS researchers at Clay Center, Nebraska identified all of the genes that were expressed by placental epithelial cells during late pregnancy and the relative expression of each gene was measured using comprehensive mRNA sequencing. Numerous genes of known nutrient transport proteins and genes known to be involved in changing tissue architecture (epithelial layer folding) were found to be expressed. This basic information will guide future research to improve placental development and function, with the goal of reducing the incidence of low birth weight piglets.
4. In vitro development of preimplantation porcine embryos using alginate hydrogels as a three-dimensional extracellular matrix. In the pig, the pre-implantation period of pregnancy is characterized by several developmental hallmarks that have significant impacts on embryo survival, uterine capacity, and subsequent preweaning piglet survival. One significant hallmark is the elongation of the pig embryo that is critical for signaling maternal recognition of pregnancy and establishment of adequate embryo spacing. Deficiencies in pig embryo elongation contribute to ~20 percent of embryonic loss, but the exact mechanisms of elongation are poorly understood partly due to the difficultly to replicate in vitro. In collaboration with researchers at the University of Nebraska in Lincoln, ARS researchers at Clay Center, Nebraska have established a culture system using alginate hydrogel as a three-dimensional matrix that facilitates morphological changes and gene regulation of pre-implantation pig embryos consistent with in vivo elongation. This alginate culture system can serve as a tool for evaluating specific mechanisms of embryo elongation, which could assist in identifying methods to improve pregnancy outcomes in the pig.
5. Identification of factors contributing to variation in growth and development of gilts. Approximately 20% of female pigs selected for breeding (gilts) fail to reach puberty or become pregnant. ARS researchers at Clay Center, Nebraska, identified changes in blood concentrations of the metabolite plasma urea nitrogen (PUN) that link growth with age at which gilts reach puberty. Using PUN in genetic selection programs will increase feed efficiency and producer profitability while reducing excretion of nitrogen, which minimizes the environmental impact of pork production, because blood concentrations of PUN are directly related to efficiency of nitrogen retention in the body (i.e. increased lean growth and decreased nitrogen excretion).
6. Relative abundance of two types of modified DNA bases from porcine tissues. Mammalian DNA contains two methylation marks in the form of modified cytosine bases that are not distinguished by traditional sequencing approaches. Researchers at Clay Center, Nebraska estimated the total abundance of each unique base using commercially available kits on eleven tissues from two diverse breeds of pigs. Analyses indicated that profiles of the two bases were substantially different in tissues of the central nervous system, perhaps indicating a greater role of the modified bases in physiological functions of these tissues. These results highlight the need to measure both modified bases and the abundance profiles generated were necessary prior to estimation of the impact of maternal dietary treatments for future experiments.
Freking, B.A., Purdy, P.H., Spiller, S.F., Welsh, C.S., Blackburn, H.D. 2012. Boar sperm quality in lines of pigs selected for either ovulation rate or uterine capacity. Journal of Animal Science. 90(8):2515-2523.