Location: Reproduction Research2008 Annual Report
1a. Objectives (from AD-416)
1] Develop techniques to predict boar fertility and potential for sperm production at an early age and discover seminal plasma protein markers associated with successful cryopreservation of boar sperm. 2] Develop strategies to improve uterine capacity, the farrowing process, and neonatal piglet survival to increase the number of piglets weaned per sow. 3] Improve sow longevity by determining the role of prepubertal growth and development of gilts and mammary involution after weaning on the efficient return to estrus of the postpartum sow.
1b. Approach (from AD-416)
Changes in testicular composition and volume will be monitored during pubertal development to establish their relationship with testicular size and sperm production at maturity. Histological approaches and ultrasonography in combination will be used to develop a non-invasive protocol. Genomic scans on these same boars will identify QTL associated with sperm production. In a sub-population of these boars, individual differences in viability of sperm cells will be assessed during cold storage and following cryopreservation. A series of experimental approaches will investigate uterine capacity. RNA from placental tissues collected between days 25 to 45 of gestation from lines of pigs selected for ovulation rate or uterine capacity will be hybridized to porcine arrays to yield expression differences in the placental transcriptome related to line and stage of gestation. Identification of polymorphisms in differentially expressed genes will establish haplotype associations for uterine capacity and fetal survival. A catalog of imprinted genes will be established for porcine placenta and evaluated for coding region polymorphisms identified in Meishan x White Composite embryos. The contribution of placental fold development to placental efficiency will include gene sequence variation in hyaluronidase and heparanase and the association of this variation with differences in litter size and piglet birth weights. Laser capture micro-dissection combined with suppressive-subtraction hybridization will define expression differences between placental trophoblast cell types during late gestation. Impact of farrowing intervals on stillbirths will be monitored with 24-hr video recording of parturition and correlated with piglet survival and growth during lactation. A second experiment will investigate the effect of dietary creatine on farrowing intervals, stillbirth, and preweaning survival. Further investigation will include treatment of late pregnant sows with monoclonal antibodies against the alpha subunit of the porcine insulin receptor to interfere with insulin binding to its receptor with the goal of increasing fetal, blood glucose concentrations. Additionally, the variation among sows in their ability to recover from a glucose challenge will be associated with subsequent piglet fat levels and liver glycogen levels at birth and preweaning survival. Reciprocal transfer of embryos from Meishan and crossbred gilts will explore the contributions of embryonic and maternal genotypes on development of neonatal pigs and growth of piglets prior to weaning. This will define molecular markers (genes and proteins) within uterine, fetal, and placental tissues during late gestation to examine in subsequent studies for their association with perinatal piglet survival. The association of weaning to estrous intervals with growth characteristics and age at puberty will be assessed in conjunction with determination of plasma urea nitrogen and creatinine as markers of muscle turnover. Plasma leptin and glucose will be monitored as markers for metabolic status. DNA will be genotyped and analyzed for QTLs associated with age at puberty and days to estrus after weaning.
3. Progress Report
Morphological evaluation of testes and measurement of sperm production for 330 BX boars have been performed and the data will be used for QTL analyses of these traits. Litters of piglets from reciprocal embryo transfers between Chinese Meishan (MS) and White crossbred (WC) pigs have been generated for an analysis of effects of maternal and fetal breeds on piglet body composition, tissue glycogen content and serum components. The required laboratory analyses for this experiment are ongoing. Age at puberty, ovulation rate, farrowing intervals and postweaning return to estrus data continue to be collected for the USMARC BX population of pigs. These data will also be used for subsequent QTL analyses for these traits. The role of basic fibroblast growth factor (FGF-2) in placental development and vascularization is being explored. The effect of sow and piglet vocalizations during lactation on piglet nursing behavior and growth rate is currently being tested in collaboration with scientists at North Carolina State University. These ongoing experiments contribute to National Program 101-Food Animal Production Action Plan; Component 1: Understanding, Improving, and Effectively Using Animal Genetic and Genomic Resources; Problem Statement 1D: Develop and Implement Genome-Enabled Genetic Improvement Programs; and Component 2: Enhancing Animal Adaptation, Well-Being and Efficiency in Diverse Production Systems; Problem Statement 2B: Reducing Reproductive Losses.
1. Sertoli cell differentiation in prepubertal boars Mature testicular size and daily sperm production in boars is limited by the number of Sertoli cells acquired before puberty; thus, non-invasive techniques are needed to identify young boars with the greatest potential for sperm production as adults. In 90-day-old boars, we discovered that the pattern of differentiation of Sertoli cells within the testes progressed from the inner region of testis toward the exterior and that when the mean diameter of the seminiferous tubules achieved 100 µm in the inner region, proliferation of Sertoli cells apparently ceased. This is the first report of this distinct pattern of Sertoli cell differentiation within the testes of any mammalian species. These data will contribute to genetic evaluation of this population of boars to identify markers for sperm production. These studies contribute to National Program 101-Food Animal Production Action Plan; Component 1: Understanding, Improving, and Effectively Using Animal Genetic and Genomic Resources; Problem Statement 1D: Develop and Implement Genome-Enabled Genetic Improvement Programs; and Component 2: Enhancing Animal Adaptation, Well-Being and Efficiency in Diverse Production Systems; Problem Statement 2B: Reducing Reproductive Losses.
2. Comparison of conceptus development in lines of pigs selected either randomly, for ovulation rate, or for uterine capacity Litter size is an important factor determining the productivity of sows, which has a significant economic impact for the swine industry. The two main factors that limit litter size include ovulation rate and uterine capacity. Gilts selected for increased uterine capacity have improved prenatal survival while gilts selected for increased ovulation rate have decreased prenatal survival. The objective of the present study was to evaluate embryo development during embryo elongation, a critical time point during gestation, as a potential contributing factor to differences in prenatal survival among selection line pigs. The findings of this study indicated limited differences between selection lines in embryo development during embryo elongation and suggest that mechanisms involved in generating line differences in survival rate are likely manifested later in gestation. Determination of the mechanisms controlling prenatal survival will allow improvements in litter size in pigs. This experiment contributes to National Program 101-Food Animal Production Action Plan; Component 2: Enhancing Animal Adaptation, Well-Being and Efficiency in Diverse Production Systems; Problem Statement 2B: Reducing Reproductive Losses.
3. Expression profile of placental tissue associated with selection for uterine capacity. Uterine capacity in pigs was improved by direct selection over 11 generations but the underlying mechanism(s) of that change is(are) not known. We generated experimental data using Affymetrix porcine micro arrays to document expression patterns of the placental transcriptome temporally from day 25 to day 40 of gestation and between the selected line and a contemporary unselected control population. A total of 4171 targets on the array exceeded statistical limits for the effect of gestational age with 2230 targets up-regulated and 1839 down-regulated from d 25 to d 40. Two targets, LIM domain and actin-binding protein 1 (LIMA1) and a hypothetical transmembrane protein differed between lines. Both genes appear to play roles in cell migration, suggesting participation in early placental development. This information is of value to the industry to address the genetic control of embryo or fetal survival. Improving fetal survival represents an opportunity to improve efficiency and profitability of the swine industry. This experiment contributes to National Program 101-Food Animal Production Action Plan; Component 2: Enhancing Animal Adaptation, Well-Being and Efficiency in Diverse Production Systems; Problem Statement 2B: Reducing Reproductive Losses.
4. Effect of empty uterine space on farrowing intervals Stillbirth rates are associated with prolonged farrowing intervals of individual piglets, and farrowing intervals are negatively associated with litter size. Understanding why small litters result in prolonged farrowing intervals could provide clues to factors controlling farrowing intervals. One aspect of small litters that could prolong farrowing is the presence of empty space within the uterus, resulting in uterine sections having smaller diameter than areas in which fetuses are present. We tested whether these constricted areas delay farrowing by eliminating fetuses on day 35 of gestation either ahead of (i.e., cervical region) or behind (i.e., ovarian end) the remaining piglets. This treatment was successful in creating restricted regions either ahead of or behind the remaining piglets; however, farrowing intervals did not differ between the two treatment groups. An unexpected result was that placenta and fetuses adjacent to eliminated fetuses were significantly larger than placenta and fetuses not adjacent to the eliminated fetuses, indicating that loss of a fetus during early pregnancy benefits adjacent fetuses. Thus, uterine constriction resulting from the loss of fetuses during early pregnancy does not contribute to prolonged farrowing intervals, and the early loss of fetuses within the uterus may benefit the development of adjacent fetuses. This experiment contributes to National Program 101-Food Animal Production Action Plan; Component 2: Enhancing Animal Adaptation, Well-Being and Efficiency in Diverse Production Systems; Problem Statement 2B: Reducing Reproductive Losses.
5. The effect of dietary energy source of manufactured liquid diets for early-weaned pigs. Twenty-three percent of the mortality during the pre-weaning and nursery phases is attributed to malnutrition. The overall goal of the swine nutrition program is to improve neonatal and weaned piglet growth and survival though nutrient management. Specifically, our goal is to increase muscle growth through dietary management of piglets. We determined that pigs receiving a low-fat liquid diet beginning at 10 d of age have modified cellular signaling for increased protein synthesis, which should lead to an improved utilization of amino acids. This finding improves our understanding of the characteristics of immature muscle that are responsible for its uniquely high rate of protein synthesis and will aid in the development of approaches for promoting muscle protein synthesis at all stages of production. This experiment contributes to National Program 101-Food Animal Production Action Plan; Component 2: Enhancing Animal Adaptation, Well-Being and Efficiency in Diverse Production Systems; Problem Statement 2B: Reducing Reproductive Losses.
5. Significant Activities that Support Special Target Populations