Oocyte quality and embryo survival are impaired when sows mated in lactation lose more than five percent of their body weight

The later stages of sow ovarian follicle growth and ovulation are normally inhibited by piglet suckling and the high metabolic demands of milk production during lactation (Quesnel 2009). Stimulating a fertile oestrus in lactation presents an opportunity to increase piglet weaning age without impairing farrowing frequency. Although lactation body weight (BW) loss is known to affect oocyte quality, follicular development and sow fertility after weaning (Quesnel 2009), no studies have investigated the effect of high BW loss on the quality of oocytes shed during an oestrus in lactation. This study tested the hypothesis that a high BW loss during lactation would reduce the capacity of sow oocytes collected on d 21 of lactation to develop in vitro and reduce embryo survival in vivo when sows were mated in lactation.

A total of 98 Large White × Landrace multiparous sows (parity 3.3 ± 0.2, mean ± SEM) was studied, with sows slaughtered at one of two time points; d 21 post-partum (prior to expected lactation oestrus expression in some proportion of sows; n = 39), or d 30 after being bred at their lactational oestrus (n = 47). Twelve sows (20%) did not express lactational oestrus and were returned to the breeding herd. On d 1 and 21 of lactation and at the first sign of lactation oestrus, sow BW was recorded. From d 18 until slaughter on d 21, or until expression of lactational oestrus and breeding, sows received 15 min of full physical boar contact daily. Ovaries were collected from sows slaughtered on d 21 and all follicles larger than 4 mm were aspirated. Recovered cumulus-oocyte complexes were matured and fertilised in vitro. Cleavage rate was recorded 28 h after fertilisation, and the stage of embryonic development was assessed on d 6 after fertilisation. All other sows were artificially inseminated (AI) at first detection of oestrus in lactation. On d 30 after AI, sows were slaughtered, ovulation rate was recorded, and embryo survival was calculated as the number of embryos as a proportion of the number of corpora lutea. Sow BW loss was calculated as the percentage of d 1 BW lost at either d 21 post-partum or at lactational oestrus. Data were analysed using a univariate general linear model with sow as the experimental unit (IBM SPSS, Version 20.0; USA).

The percentage BW loss did not affect the time taken for sows to express lactational oestrus (22.7 ± 0.24 days). However, sows that lost more than 5% of their BW had reduced blastocyst development in vitro and poorer embryo survival in vivo (Table 1). Data collected from the present study suggest that greater BW loss over lactation reduced oocyte quality and embryo survival, without affecting follicle size and ovulation rate, when sows were mated before weaning. This supports previous studies (Quesnel 2009) that showed higher BW loss during lactation consistently results in reductions in early embryo survival when sows are mated after weaning. This is likely the result of an impaired follicular environment in which the oocyte matures.

Table 1.  The effect of sow body weight (BW) loss over lactation on embryo cleavage and blastocyst development in vitro, and ovulation rate and embryo survival in vivo. Values are means ± SEM