THE ONSET OF HEAT AFTER WEANING, HEAT DURATION, AND OVULATION AS MAJOR FACTORS IN AI TIMING IN SOWS

The purpose of the study was to gain experience in the use of transcutaneous sonography in the examination of the ovaries of breeding sows and to obtain further knowledge in ovulation and its time relationship to the onset and duration of estrus after weaning. Weaned sows were examined at the Hulsenberg research station by means of a combined estrus-detection system (0800h, 1500h, 2200h) with a teaser boar to determine the onset and end of estrus. The detection of ovulation was performed simultaneously by sonography of the standing sow using a 5 Mhz sector scanner. The highest percentage of successful examination of the ovaries (over 90%) was obtained at the end of the 16-week observation period, corresponding to the increase in experience. A total of 481 from 483 weaner sows presented a heat duration of between 32 h and 96 h, while 2 sows showed heat periods of longer than 4 days. Sows coming into heat early after weaning showed statistically longer heat periods than sows entering heat later. In 88.4% of the sows with detected onset and end of heat, ovulation could be determined (427 sows). Of these animals, one sow ovulated earlier than 24 h after the onset of heat, 7.3% ovulated at 24 h, 82.4% of the sows ovulated at between 32 and 56 h, 9.5% at between 64 and 96 h after initiation of standing heat, and 2 animals (0.5%) ovulated later than 96 h after the onset of heat. No ovulations occurred after cessation of standing estrus. Approximately 80% of the sows came into heat within 3-5 days after weaning and more than 77% of the animals ovulated within 5-7 days after weaning. For practical application in AI the following recommendation can be established: Sows coming early into heat after weaning (day 3-4) show estrus over 3 days, so inseminations must be begun on day 2-3 of heat. Sows with an average interval from weaning to onset of heat (5 days) present a heat period of approximately 2 days and should be inseminated 24 h after heat onset, the second insemination to be done 12 h later. Sows entering heat late after weaning (day 6 and beyond) tend to show heat only for a short period (1 day), indicating that insemination should be performed within 24 h after heat detection. A second insemination is usually not necessary.