Does absence make the heat grow stronger?

By Lucy Campbell, Animal Scientist, ACMC - If we are talking about ‘segregated service management’, then J.R. Behan and P.F. Watson would say “Yes”, as is detailed in their article ‘The effect of managed boar contact in the postweaning period on the subsequent fertility and fecundity of sows’.
calendar icon 12 June 2006
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ACMC Breeders

Generally, on farm, weaned sows are given partial access to boars to encourage the expression of the standing response, as an indicator of oestrus. However, it has been reported by a number of authors that continual contact with boars may have an adverse effect as the sows can become ‘used’ to the boars’ stimulus, leading to inaccurate oestrus detection and thus, inaccurate timing of insemination. ‘Segregated service management’ is the technique of segregating the sows from the boars for 4 days post-weaning. On the fourth day and upon contact with the boar, it is thought that the sow will display stronger behavioural and physiological responses and thus have an impact on fertility and fecundity.

Behan and Watson carried out an investigation to test this theory and concluded that this segregation system resulted in insemination being more closely related to ovulation. In this study there was a highly significant increase (p<0.001) in farrowing rate and a highly significant increase (p<0.001) in mean litter size of more than 0.3 piglets, in the sows that were being segregated from the boars until 4 days post-weaning.

It has been suggested that early insemination (in relation to ovulation) results in a proportional reduction of the number of oocytes fertilised. Behan and Watson therefore suggested that delaying the insemination of those sows that would display the standing response during the first 4 days post-weaning until after the fourth day, would result in an improved fertility. In the article, Behan and Watson discuss the potential role of hormones on this improved fertility of segregated sows. They suggest that removing the initial stimulation by the boars immediately after weaning, ensures that sows have not exhausted the availability of essential hormones or inhibited pathways for their release at the point of later stimuli, when the sow is well into the period of oestrus.

With the suggestion of oxytocin being the primary hormone released following olfactory boar stimulation and the fact that this hormone plays a role in uterine contractions, thus aiding semen transport, it seems to make sense that delaying this initial boar stimulation until a time closer to ovulation will result in increased fertility. Ensuring that the sow is not stimulated by the boar, and thus not releasing oxytocin, until the optimum time for insemination, guarantees that the full potential of these hormones/pathways are utilised (and indeed that they are still available to the sow) as they are required and will therefore increase the sow’s fertility.

This article highlights the role of managing boar contact to maximise profitability on pig breeding units. Behan and Watson suggest that the results of this investigation and others alike may well shape the future design of service houses to ensure that sows show signs of oestrus at the optimal time for insemination, rather than in the very early stages of oestrus, where insemination may be less fruitful.


J.R. Behan & P.F. Watson. The effect of managed boar contact in the post-weaning period on the subsequent fertility and fecundity of sows. Animal Reproductive Science 2005 88: 319-324.

Source: ACMC - June 2006

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