Location: Reproduction Research2012 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:
This is the final report for the 5 year project 5438-31000-084-00D, which ended 2012, and was replaced by 5438-31000-091-00D. The collection of reproductive phenotypes has been a significant activity of this project. Phenotypes collected included age at puberty (including complete failure), birth intervals during farrowing, stillbirth rate, post weaning return to estrus, litter size at birth, and preweaning survival. Genomic association results are now available for age at puberty and puberty failure, litter size, stillbirth rate, average birth weights, and post weaning return to estrus. Analyses for birth intervals are currently in progress. All efforts to examine boar fertility in the project ended with the retirement of the scientists involved in that work. Before retirement, scientists demonstrated that ultrasound was not useful as a predictor of testis size, testes development, or sperm production. A new scientist was hired to perform research in gilt development, which is a stated reproductive priority of the National Pork Board. Research to address the number of piglets weaned had numerous accomplishments. Hyaluronan, hyaluronidase, and heparanase in placental tissues were examined throughout gestation in large and small fetuses, and results suggested that changes in these placental stromal matrix components may contribute to differences in placental development between large and small piglets. Microarray analyses to compare placental gene expression between lines of pigs selected for uterine capacity and randomly selected control lines indicated two differentially expressed genes. Work on birth intervals and stillbirth demonstrated that birth intervals up to an hour do not affect the incidence of stillbirth. Other results indicated that the effects of estrogen, birth weights and empty uterine space were not responsible for the decrease in birth intervals with increased litter size. It was also confirmed that specific regions of the brain were undermyelinated in low birth weight piglets, and that creatine supplementation of sows during late gestation improved myelination. A simple technique for measuring piglet serum immunoglobulin was developed to assess whether piglets obtained sufficient colostrum. Results of this assay were predictive of preweaning mortality. Subsequent results indicated that the technique can be used in a commercial setting to monitor colostrum management and to identify sows that fail to initiate colostrum production. Research to address puberty and postweaning return to estrus was also affected by retirement of a scientist. A new scientist was hired to continue work on postweaning return to estrus. Relationships between various metabolites (plasma urea nitrogen, creatine, choline, serum albumin, lactose) and postweaning return to estrus were investigated. QTL for some of these metabolites were found to overlap with postweaning return to estrus, suggesting that they may participate in some way in controlling return to estrus in pigs. Further work assigned to this project demonstrated that lysozyme fed to young piglets was an effective replacement for antibiotics and could be used to reduce antibiotic usage.
1. Lysozyme as an alternative to subtherapeutic antibiotics in nursery swine feed. The addition of antibiotics to swine diets benefits producers by improving feed efficiency and decreasing susceptibility to bacterial infections. Because of concerns over antibiotic resistance, alternatives to antibiotics are a high priority for U.S. swine producers. ARS researchers at Clay Center, Nebraska, determined that feeding a natural antimicrobial, lysozyme, to nursery pigs was as effective as antibiotics in increasing growth performance and feed efficiency, as well as improving gastrointestinal health. The identification of suitable alternatives to antibiotics will enable the swine industry to effectively transition away from dietary antibiotic use. Thus, lysozyme is a suitable alternative to antibiotics for nursery pigs.
2. Plasma urea nitrogen and age at puberty in pigs. Almost half of all breeding age females are culled from swine herds each year due primarily to infertility costing the swine industry between $70 and $110 million annually. Gilts that reach puberty early are more fertile and have greater productivity and longevity; thus, research to predict early age at puberty has great merit to increase efficiency and profitability of pork production. ARS researchers at Clay Center, Nebraska, discovered that gilts with greater concentrations of a blood metabolite called plasma urea nitrogen reached puberty sooner than gilts with lesser concentrations. Plasma urea nitrogen could be measured at 5 months to rank gilts on their predicted age at puberty allowing producers to select females for breeding that have a higher probability of remaining in the herd longer and producing more pigs.
3. Effect of selection for uterine capacity on uterine traits. Continued selection for increased litter size has resulted in sows that produce more ova (eggs) than their uterus has capacity to support as fetuses. This overcrowded uterine environment results in increased fetal loss and reduced birth weights of piglets putting them at greater risk of postnatal death. These inefficiencies are estimated to cost the swine industry over $600 million annually. ARS researchers at Clay Center, Nebraska, discovered that prior to reaching sexual maturity, gilts from a line of pigs selected for increased uterine capacity had reproductive tracts that were longer in length and larger in diameter compared with control animals. Methods to measure these uterine traits in prepubertal gilts can be developed allowing producers to select females that have greater uterine capacity and give birth to well developed, healthier piglets.
4. Successful monitoring of a colostrum management program in a commercial swine herd. Survival of piglets before weaning can be improved by managing a piglet’s access to colostrum (the first milk produced by sows) during the first day of life. Several colostrum management programs exist, but commercial pig producers lacked a simple method to test whether they work. ARS researchers at Clay Center, Nebraska, in collaboration with a commercial producer, used a simple technique developed by ARS (the “immunocrit”) to assess whether a colostrum management program improved colostrum intake by piglets. Use of the immunocrit test indicated that the colostrum management program reduced the number of piglets that received insufficient colostrum, and this improvement was associated with improved survival during early life. The study demonstrated that the immunocrit test can be used in commercial herds to monitor the effectiveness of colostrum management programs.
5. Discovery of genetic markers that can be used to improve sow reproduction. Excessive weight loss during lactation can have adverse effects on subsequent reproductive performance in sows. ARS scientists at Clay Center, Nebraska, found that weaning-to-estrus interval, or the period of time from when nursing piglets are removed until rebreeding, was related to DNA mutations from genes involved in fat production. These discoveries were made publicly available and have been published in Animal Genetics. These markers can be used for selection and management strategies to identify females that will have greater probability of staying in the breeding herd longer thereby reducing input costs for producers.
6. A comparison of piglet growth and blood profiles during early life between Chinese Meishan and White crossbred gilts. Crossbreeding studies between Chinese Meishan and Large White pigs have demonstrated that characteristics of the Chinese Meishan breed of piglet are associated with improved survival during early life; however, piglet growth rates were increased due to the characteristics of the Large White breed of sow. ARS researchers at Clay Center, Nebraska, further investigated the contributions of the breed of the piglet and/or sow and their interactions on piglet growth and blood profiles likely to influence growth and survival. This study confirmed that piglet growth was greater due to White crossbred sows. However, piglet blood nitrogen and fat levels, which are related to growth and improved survival of piglets, respectively, were influenced by both the Meishan piglet and Meishan sow. Thus, results suggested that the Meishan sow is responsible for slower growth of piglets, while the Meishan piglet is responsible for improved preweaning survival.
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