This project significantly improved our understanding of the interaction between HS and reproduction in sows and gilts and the potential relationship with seasonal infertility.
1) In Objective 1, we demonstrated that seasonal infertility in large commercial pork production system was not strongly correlated with HS during the wean-to-estrus interval (WEI).
a. We are now pursuing strategies and funding to determine the impact that the lactation environment has on P1 weaned sow reproductive performance in the summer.
2) In Objective 1, we did not see differences in circulating LPS binding protein (LBP) or insulin during the WEI of sows weaned during the summer or spring.
a. This is important in strengthening our understanding of the biological consequences of the lactation to gestation transition during different seasons.
3) In Objective 2, we demonstrated that thermoregulatory response to HS is repeatable in gilts exposed to HS more than 4 months between exposures.
a. This was a critically important finding for the pork industry. Subsequently, our group has leveraged this project and samples collected during it to secure additional dollars to pursue the identification of specific genomic regions in pigs associated with contributing to production efficiency during HS.
4) In Objective 2, we demonstrated a lack of impact on HS during a Matrix synchronized follicular phase.
a. Based on this project we are now hypothesizing that seasonal infertility manifests itself through the combination of seasonal, environmental, metabolic conditions, and genetics of the sows.
5) In Objective 2, we determined that HS during the follicular phase did not affect 17β-estradiol production in the follicle but altered proteins involved in ovarian physiology. However, gilts susceptible to HS, as determined by their thermoregulatory response, did have reduced corpora lutea size, which could have implications for pregnancy maintenance and litter-size.
The execution of this important research has advanced our understanding of the seasonality of swine reproduction. These meaningful results will have both an immediate and long-term value to U.S. Pork Producers. Data produced from these experiments is providing a foundation for future experiments that will identify valuable markers for reproductive success during seasonal infertility enabling the development of mitigation strategies. In addition to generating a much needed understanding of the immediate effects of HS during the WEI, we also expect to enhance basic understanding of the detrimental effects that HS has on porcine oocyte development which is foundational for future applied swine management and production practices.
Approximately 300,000 P1 sows are weaned during the period of seasonal infertility in the US, and based on this project, seasonal infertility causes a 17% reduction in litters produced due to a combination of both lower breeding rates and farrowing rates. This represents a tremendous opportunity to improve the efficiency of the US swine herd. Moderately reducing these losses from 17% to 12% during seasonal infertility represents nearly 400,000 piglets produced while requiring fewer replacement females, creating opportunities for more rapid genetic advancement. We are continuing to pursue mitigation strategies through current projects and project proposals submitted to the National Pork Board. This research project has made an extremely valuable impact on our research efforts leading to the development of mitigation strategies.