Date Full Report Received06/01/2014
Date Abstract Report Received06/01/2014
Funded ByNational Pork Board
Numerous factors, including herd-life (length in days), removal parity, total piglets born and the number of piglets weaned, impact sow productive lifetime. Like many complex traits that are controlled through numerous loci and that are subject to environmental influence, sow productive lifetime can be lowly heritable. This project was conducted to facilitate the identification of physical and blood markers that could be utilized by the swine industry through incorporating this information into the replacement gilt population. The objectives of the project were to determine if specific, easily identifiable factors could be reliable in identifying gilts for the replacement pool that have a high probability of achieving their first estrus prior to 180 days of age. The data in this project demonstrate that by approximately 95 days of age, gilts begin to demonstrate a high degree of variation in the amount of follicular activity, absent at 75 days of age. The variation in follicular activity appears to impact the growth and development of the reproduction tract which can be observed by variation in vulva size. On day 95 of age, only 31% of gilts whose vulva size was more than one standard deviation below the mean achieved their first estrus by 180 days of age, compared to 66% of all other gilts. However, the variability in vulva size at day 75 of age was not useful in identifying gilts that are likely to achieve their first estrus by 180 days of age. Additionally, kisspeptin, a molecule associated with activation of the hypothalamic-pituitary-gonadal axis, was greater on days 75 to 105 of age in gilts that achieved their first estrus by 200 days compared to those that did not. Collectively, we have identified a time point in gilt development when decisions regarding the inclusion or exclusion of gilts in the replacement gilt pool could be made that may reduce the number of non-productive days in the sow herd as age of first estrus is one of the best indicators of sow lifetime production.
• During postnatal ages of 75 to 115 days of age, gilts undergo ovarian follicular reorganization as assessed by having the presence of tertiary follicles.
• Of gilts that achieved their first estrus by 200 days of age, a weak but statistically significant correlation between body weight at 75 days of age of first estrus was observed.
• Changes in vulva development during days 95 to 115 of age, presumably driven by estrogen production from tertiary follicles, may be a useful tool in identification of gilts to include or exclude in a gilt replacement pool.