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When Is The Best Time To Breed Sows?

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Bernie Peet is president of Pork Chain Consulting Ltd. of Lacombe, Alberta, and editor of Western Hog Journal.

A correctly timed breeding is the cornerstone of productivity in the swine herd. The timing of natural service or insemination has a significant effect on farrowing rate and litter size. Service timing regimes are determined by a several individual farm factors and consequently will differ from farm to farm. By understanding some of the factors that influence service timing, the optimum regime can be determined.

Timing is usually defined in relation to the start of standing oestrus in gilts and sows. According to research studies, the length of standing oestrus may be as short as 24 hours in gilts (range 24-48 hours) or as long as 72 hours in sows (range 48-72 hours). Ovulation – the release of eggs from the ovaries into the fallopian tubes – takes place about 70 per cent of the way through standing oestrus. Once released, ova only have a life of about 8-10 hours if not fertilized, therefore service regimes aim to have viable sperm in the fallopian tubes prior to the time of ovulation.

Fortunately, sperm remain viable for at least 24 hours which is why many service regimes are based on matings at 24-hour intervals. The difficulty in determining service regime is that the length of standing oestrus varies so much and consequently the timing of ovulation also varies relative to the start of standing heat.

Detecting the onset of standing oestrus is therefore the key to service timing. If heat checking is carried out once per day, the sow could have been in standing oestrus for up to 20 hours, but with twice-a-day checking she is unlikely to have been standing for more than 12 hours. Twice-daily heat-checking therefore identifies the start of standing oestrus more accurately. Depending on other factors, this may allow breeding to be delayed in order to achieve the optimum timing.

Timing for gilts

Gilts show a shorter oestrus period than sows, therefore the timing of breeding will be different. In many situations, depending on the average length of oestrus on the specific farm, the first mating will take place immediately standing heat is detected. Where heat checking is carried out twice per day, a delay of 12 hours after standing oestrus is detected may be practised, providing the average length of gilt oestrus for the farm is adequate.

First-litter weaned sows also tend to have a longer wean to service (W-S) interval and shorter heat periods than older sows and so may be treated in the same way as gilts as far as service timing is concerned. Sows from their second weaning onwards are likely to stand for at least 48 hours and usually 60-72 hours, so some delay between heat check and first mating is desirable, especially with twice per day checking. Sows that return to service, or that show oestrus after having reproductive problems such as being pregnancy test negative, not-in-pig or abortion are often slightly sub-fertile and have a shorter oestrus than weaned sows. In most situations, the normal procedure should be to breed these females immediately standing heat is detected.

For sows, the W-S interval has a big effect on the length of standing oestrus and therefore the optimum timing for breeding. Sows which exhibit a short W-S interval exhibit a longer oestrus period than those which take longer to show signs of heat, so first breeding can be delayed. Typically, sows detected on heat four days after weaning can be delayed for 24 hours, those on heat on day five after weaning can be delayed by 12 hours and those exhibiting standing heat on day six or later should be bred immediately. From days 8-14 post-weaning, the sow has a sub-fertile period and has a lower chance of conceiving. She is also likely to have a relatively poor subsequent litter size compared to sows mated in days one to seven and 15-21 post weaning. As this effect is quite pronounced, some farms have a policy of not breeding sows in the sub-fertile period.

Lactation feeding important

Because maximum fertility occurs in the four to seven days after weaning it is very important that a high percentage of weaned sows are bred by seven days post-weaning, ideally 95 per cent and a minimum of 90 per cent. Attention to lactation feeding, in particular, will help to ensure that the average W-S interval and the degree of variation is minimized.

Once standing heat has been detected and the timing of the first breeding is determined, the question is how many further breedings should be carried out and how they should be timed. Because semen remains viable for 24 hours in the reproductive tract, further breeding at 24-hour intervals is usually effective. Some trials have shown a benefit of breeding twice on the day after the first service in order to get closer to the time of ovulation, but the possible improvements in productivity will vary from farm to farm and also need to be evaluated alongside the additional cost of an extra breeding.

Finally, the key to good service timing is accurate and timely detection of oestrus in order to identify the start of standing heat as accurately as possible. This will allow the correct service timing regime to be applied consistently. My experience suggests that poor farrowing rate and litter size is more likely to be due to inadequate heat checking than to the actual timing of matings.

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