Swine Reproduction Papers
It has been known for quite a while that breeding close to the time of ovulation (egg release from the ovary) improves the chances for farrowing and larger litter size. This occurs because the time period that eggs can be fertilized is limited to only 8-12 h after ovulation. Fertilization of older eggs or fertilization with aged sperm results in reduced embryos that survive to become fetuses. Sperm are able to fertilize eggs effectively within 24 h after deposition into the female reproductive tract, provided that extended semen is not used beyond the recommended expiration date. However, the challenge has always been to time the insemination so that deposition of sperm occurs approximately 12 h prior to the time of ovulation. It is important for sperm to be present in the female tract before ovulation since they must travel to the site of the eggs and also must undergo changes in the female tract that allows them to fertilize eggs.
To date, the best marker for time of ovulation has been estrus. Unfortunately, estrus can last from 1-3 days in pigs, and this large variation in the duration of estrus prevents prediction of ovulation or optimal time for a single insemination. In light of these problems, efforts have focused on methods to that could reduce or even predict the variation in time of ovulation. Data from our lab indicates that the time of ovulation in sows cannot be predicted to high degree of accuracy because many factors including: season, genetics, management, parity, and wean to estrus interval, influence the time from estrus to ovulation.
One method that has been investigated to reduce this variation was treating sows with PG600 at weaning. PG600 improved the percent of sows that returned to estrus compared to untreated sows but exaggerated the spread in ovulation time. In PG600 treated sows, those sows that returned to estrus early (2-3 days), tended to be in estrus longer and ovulate later (56-60 h) after onset of estrus. The majority of PG600 treated sows returned on day 4 and these sows ovulated about 47 h after onset of estrus. Sows that returned later (5-6 days) were in estrus a shorter period of time and ovulated earlier (18-35 h). In non-treated sows, the early returning sows (3 days), did not ovulate later (45 h) than those returning at 4 days (47 h) and 5 days (42 h). But, even in control sows, those returning late, on day 6, ovulated early at 31 h after onset of estrus.
Within the last few years, data from Europe, the U.S. and Canada, have indicated that gilts ovulate 87% and sows ovulate 70% of the way through estrus. On a practical note: this means that if estrus detection is performed at frequent enough intervals, close prediction of the time of ovulation could be obtained. This information would be very useful for determining whether breeding protocols in use were optimized for insemination of females within an 18-h period before the time of ovulation.
Our current efforts at the University of Illinois are focused on determining the influence of estrous detection frequency (once, twice or three times daily), in conjunction with real-time ultrasound (performed every 8 hours) to determine actual time of ovulation. Our objective is to assess how accuracy of onset of estrus affects our ability to inseminate near the optimal time in the weaned sow population. Our data will include conception rate, farrowing rate, and litter size in response to the effect of treatment for enabling inseminations to occur within 18 h of ovulation.
Robert Knox is an assistant professor, and Kilby Willenburg and Gina Miller are graduate students in the Department of Animal Sciences.