Location: Reproduction Research2010 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
Most of this project is dedicated to genomic analysis for a variety of reproductive traits. In support of this, phenotypes for a variety of reproductive and production traits have been collected and Swine Beadchip genotyping has been completed on approximately 3000 pigs from the USMARC swine herd in the past year. Statistical analyses of these data are ongoing and should be completed within the next year. Objectives 1A and B dealing with testis development in boars are mostly complete, however a genomic analysis of sperm freezability is ongoing and should be completed within the next year. The scientist working in this area retired in January 2010. To support objective 2A dealing with placental function and uterine capacity in the pig, a reciprocal transfer study has been initiated to determine the conceptus and maternal contributions to improvements in uterine capacity due to selection for uterine capacity. A second replicate of this experiment is needed to acquire sufficient observations for valid conclusions. An experiment was also initiated to compare the uterine capacity of Meishan versus white crossbred pigs. Finally, several trials have been performed to develop an in vitro system that will allow pig embryos to undergo elongation. Elongation determines the initial size of the placenta and is therefore an essential part of placental development. To support Objective 2B, develop strategies to reduce birth intervals, creatine treatment of gilts prior to farrowing is being further tested in the July 2010 farrowing season to determine whether creatine may help improve birth intervals during heat stress. Previous work using creatine supplementation indicated that there were no effects on birth intervals in a non-heat-stressed environment. Objectives 2C, D and E all deal with improving preweaning mortality. An experiment is ongoing to determine the gestational origin of differences in energy metabolism between Meishan and white crossbred piglets. Transcriptomic analysis of the fetal liver will be examined at various times during gestation to determine when and how development of piglets in the two breeds diverge. The contribution of brain myelination and sow colostrum production and piglet colostrum intake on piglet preweaning mortality is being investigated. A recently developed test for passive transfer in piglets is being used to determine the contributions of the sow and the piglet to this vital interaction. Objectives 3A, B and C all deal with age at puberty and return to estrus post weaning. Studies of metabolic factors influencing return to estrus post weaning are ongoing. These studies include development of genetic markers in a variety of genes involved in the metabolic pathways of interest to post weaning return to estrus.
1. Neonatal piglet energy stores are dependent on the breed of the piglet, not the breed of the sow. Preweaning piglet mortality reduces the profitability of swine production and occurs primarily in low birth weight piglets. Despite decreased birth weights compared to European breed piglets, Meishan piglets have lower preweaning mortality rates. ARS scientists at the U.S. Meat Animal Research Center in Clay Center, Nebraska, used reciprocal embryo transfer between Meishan and White crossbred gilts to examine the contributions of the breed of piglet and sow and their interactions on the development of neonatal piglets. They found that at day 1 of age, there were significant piglet breed effects favoring Meishan compared to White crossbred piglets on stomach content weights; percentage of fat and nitrogen within the body composition; liver, bicep femoris, and longissimus dorsi glycogen concentrations; and serum albumin levels. Preweaning survival in Meishan piglets appears to correlate to improved energy storage and use during the neonatal period and suggests that focusing on neonatal piglet physiology regulating energy stores, appetite, and activity will identify and improve factors associated with piglet survival.
2. Association of porcine heparanase and hyaluronidase 1 and 2 with reproductive and production traits in a Landrace-Duroc-Yorkshire population. Heparanase (HPSE) and Hyaluronidase (HYAL) 1 and 2 have been shown to be biologically relevant in ovarian and placental activity. Therefore, a study was conducted by ARS scientists at U.S. Meat Animal Research Center in Clay Center, Nebraska, to determine if polymorphisms within these genes were associated with reproduction and production events in a Landrace-Duroc-Yorkshire population of pigs. Both age at puberty and weaning-to-estrus interval were associated with a genetic marker for HYAL2. Birth weights and litter size components were associated with genetic markers for HPSE, HYAL1, and HYAL2. The identified genetic markers for HPSE, HYAL1, and HYAL2 could be very useful for marker-assisted selection protocols for breeding females to determine potential fertility, litter size capabilities, and(or) piglet survivability prior to introduction into the breeding system.
3. Metabolic measurements in the sow and relationship to post-weaning reproductive performance. Excessive weight loss during lactation is an indicator of tissue catabolism in exchange for maintaining metabolic output and can have adverse effects on reproductive parameters. Therefore, scientists at U.S. Meat Animal Research Center in Clay Center, Nebraska, established blood metabolic measurements and body condition measurements at periods of physiological changes due to parturition and lactation in the sow and investigated how these components related to post-weaning reproductive performance. First- and second-litter females that lost less body weight from late gestation through weaning had greater return to estrus than those females that had substantial body condition loss. First-litter females with less increase in plasma creatine phosphokinase activity and plasma L-Lactate levels (indicators of protein degradation) from late gestation through day 1 post-farrowing had improved return-to-estrus rates within a 14-day period following weaning. Post-weaning estrus rates from second-litter females were negatively associated with backfat thickness and plasma creatine levels. These data suggest that body weight, backfat thickness, and metabolic parameters contribute to the complex trait of post-weaning reproduction and by understanding these relationships producers could more effectively manage females to ensure improved return-to-estrus capabilities of animals.
4. Development of the “immunocrit,” a simple, rapid, inexpensive method for determining whether piglets receive adequate colostrum from the sow. Preweaning mortality of piglets represents a substantial loss to swine producers and one possible factor contributing to this loss is the failure of neonatal piglets to obtain sufficient colostrum from the sow, which can be caused by either failure of the piglet to nurse or failure of the sow to initiate lactation. An inexpensive and rapid method, the “immunocrit,” was developed and validated by ARS scientists at the U.S. Meat Animal Research Center in Clay Center, Nebraska, to measure newborn piglet serum immunoglobulin G (IgG), which reflects whether a piglet has received adequate colostrum. Results indicated that immunocrit measurements are predictive of piglet mortality and litter average immunocrit indicated the ability of the sow to transmit IgG (via colostrum production). Low immunocrit values were primarily due to the failure of individual piglets to nurse and not due to failure of the sow to produce colostrum. Litter average immunocrit can be used to identify sows that fail to initiate colostrum production enabling selection for efficient IgG transfer (presumably efficient colostrum production) from sow to piglet and the immunocrit is already being used in commercial settings to monitor and manage newborn piglet colostrum intake.
5. Gromega and/or zinc supplementation of sow feeds has limited effect on newborn piglet brain myelination. Low birth weight predisposes newborn piglets to mortality, and previous results indicated that low birth weight is associated with reduced myelination of the brain stem, which could impair coordination of movement of newborn piglets and increase susceptibility to crushing by the sow. With funding from the National Pork Board, ARS scientists at U.S. Meat Animal Research Center in Clay Center, Nebraska, performed an experiment to determine whether essential fatty acid supplementation (Gromega) and/or zinc supplementation would improve brain myelination of low birth weight piglets. Combined Gromega and zinc supplementation increased myelin basic protein in myelin membranes from the brain stem, but there was no effect on myelin lipids. There were also no effects of supplementation on preweaning mortality. These results suggest that combined Gromega and zinc supplementation can improve aspects of brain stem myelination, but further research is needed to determine whether supplementation improves preweaning mortality.
6. Effect of µ-calpain deficiency on skeletal muscle development. Protein turnover requires proteolytic enzymes to degrade skeletal muscle proteins and calpain system has been identified as a potential candidate protein turnover enzyme. Researchers at the U.S. Meat Animal Research Center, Clay Center, Nebraska, reported that the proteases m-calpain and caspase 3/7 are up-regulated in skeletal muscle to compensate for the lack of µ-calpain. However at 30 weeks of age, muscle from mice lacking µ-calpain had cellular changes that indicated increased ribosomal abundance and myonuclear domain size, which shows a potential for increased protein synthesis and skeletal muscle growth. These findings improve our understanding of µ-calpain function, including interactions with other proteases, which will contribute the development of approaches for promoting the preservation and(or) restoration of skeletal muscle mass.
Vallet, J.L., Miles, J.R., Freking, B.A. 2010. Effect of Fetal Size on Fetal Placental Hyaluronan and Hyaluronoglucosaminidases Throughout Gestation in the Pig. Animal Reproduction Science. 118(2-4):297-309.