A reliable predictor of ovulation in sows is important to breeding strategies because the best time to inseminate is the 24-hour window before ovulation.
The duration of standing heat and the standing heat to ovulation interval both vary.
However, the time of ovulation during estrus is related to estrus duration.
Sows generally ovulate about 70 percent of the way through the period of standing heat. But that is not always the case.
Work at the University of Alberta Swine Research Unit found gilts ovulated 85 percent of the way through standing heat.
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U of A researchers also found that the optimal time for insemination depends on the frequency and accuracy of heat detection.
Boars were exposed to 92 gilts and heat checked every six hours.
From that data, the impact of once and twice a day heat detection on time of ovulation was extrapolated.
Researchers found that when heat checking is done less often, both the variation in standing heat duration and the estimated time from the onset of estrus to ovulation increased.
With twice-a-day heat checks (every 12 hours) most gilts ovulate between 33 and 60 hours after the onset of heat.
However, with once-a-day heat checks more gilts ovulated before 33 hours or after 60 hours.
This means that once-a-day checks are less accurate in predicting ovulation time in gilts.
With fewer checks and therefore less heat detection, more inseminations are necessary. The first insemination should take place when heat is detected.
Perfect timing
Breeding and heat detection recommendations for gilts are often based on 12-hour intervals to ensure that semen is in the reproductive tract in the ideal 12-hour interval before ovulation.
For example, when heat detection is done every 12 hours one recommendation is to inseminate 24 hours after the onset of heat and then do a second insemination 12 hours later.
From a practical standpoint these recommendations may need to be modified because there is often a 16-hour gap from the time barn staff leaves in the evening until they return in the morning.
In this situation, with twice-a-day heat detection, the recommendation would be as follows:
- For gilts that first stand at the morning heat check, breed them in the afternoon on the same day followed by morning or afternoon the next day.
- If gilts first stand at the afternoon heat check (a more accurate prediction of when heat first started,) then delay the first breeding until the next afternoon followed by morning or afternoon breeding the following day.
Delays to first breeding greater than 12 hours from the onset of estrus that result in gilts only being bred once may not be a serious concern.
Experimental results show that short heat duration is associated with a shorter interval (approximately 35 hours) to ovulation.
In this situation the single breeding should generally fall in the ideal 12-hour period before ovulation and result in good fertilization.
The key to developing a good breeding strategy is to appreciate the impact that frequency and accuracy of heat detection have on breeding success.
Adapted from work done at the University of Alberta by Fernanda Almeida, Susan Novak, and George Foxcroft Michelle Follensbee, Alberta Pork Research Centre.
