Timing of lactational oestrus in intermittent suckling regimes: Consequences for sow fertility

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Abstract

Three intermittent suckling (IS) regimes were evaluated for their effects on lactational oestrus and subsequent fertility. Control sows were weaned (CW; n = 38) at d 26 ± 2 of lactation. In IS19-7D (n = 40) and IS19-14D (n = 42) sows, IS started at d 19 ± 1 of lactation and sows were weaned 7 or 14 d later. In IS26-7D (n = 41), IS started at d 26 ± 1 of lactation and sows were weaned 7 d later. During IS, sows were separated from their piglets for 10 h/day. Oestrus detection was performed twice daily without a boar and ovulation was confirmed by ultrasound once a week. In IS19-7D, IS19-14D and IS26-7D, respectively, 50%, 64% and 61% of the sows showed oestrus and ovulation during IS (P > 0.05), and, of the remaining sows, 100%, 93%, and 69% showed oestrus in the first week after weaning. In CW sows, 95% showed oestrus in the first week after weaning. Parity 1 sows were considerably less likely than older parities (23% vs. 68%) to show oestrus in lactation. Pregnancy rate of the first post partum oestrus (during lactation or after weaning) was 89% (CW), 92% (IS19-7D), 80% (IS19-14D) and 77% (IS26-7D) (P > 0.05) and subsequent litter size was 14.5 ± 0.5, 14.5 ± 0.6, 15.3 ± 0.5 and 15.2 ± 0.8, respectively (P > 0.05). Sows mated during lactation had similar pregnancy rate and litter size to those mated after weaning. Hence, ongoing lactation for the first 2–9 d of pregnancy did not negatively affect fertility. A total of 50–64% of IS sows showed lactational oestrus, regardless of the stage of lactation. Pregnancy rates and litter size were similar to control sows, and were not affected by stage of lactation at mating.

Introduction

Sows normally remain anoestrous during lactation (e.g. Armstrong et al., 1988), and only conceive after weaning. This limits the number of litters raised per year, and as a consequence, lactation length in conventional pig husbandry has gradually been reduced to 3–4 weeks over the last few decades. This relatively short lactation period often results in a post-weaning growth check of the piglets and a greater susceptibility to diarrhea (e.g. van Beers-Schreurs et al., 1992), reducing piglet welfare. Uncoupling of the event of weaning and the next conception would allow a longer lactation, but is only feasible when sows ovulate and conceive during lactation. In recent years, several papers have evaluated the use of intermittent suckling to achieve that aim (reviewed by Gerritsen et al., 2008b). Intermittent suckling means daily separation of sows and piglets for 10–12 h/d during the last week(s) of lactation. This procedure, indeed improves lactational feed intake of piglets and post-weaning piglet performance (e.g. Kuller et al., 2004, Berkeveld et al., 2007a, Berkeveld et al., 2007b). Although lactational follicle development and ovulation occurs during IS, number of responsive sows is variable, depending on e.g. parity and breed and onset of IS (e.g. Kuller et al., 2004, Gerritsen et al., 2008b). Moreover, embryo survival and development may be negatively affected by ongoing lactation compared to weaned control sows, especially when lactational ovulation occurs within 3 weeks of farrowing and when intermittent suckling is continued for a considerable time into pregnancy (reviewed by Gerritsen et al., 2008b). Hence, the current study evaluated reproductive performance (oestrus onset, farrowing rate and litter size) during IS regimens differing in onset (d 19 or d 26 of lactation) or duration (7 or 14 d), to study the effects of the time that has elapsed since farrowing, and the effects of suckling during early pregnancy.

Section snippets

Material and methods

The experiment was approved by the Ethics committee for animal experiments of Wageningen University.

Oestrus

The distribution of oestrus is shown in Fig. 2 for the four treatments. In the 112 sows in which ultrasound was performed on a weekly basis, oestrus and ovulation were always recorded concurrently. Of the control sows (weaned at d 26), 95% (36/38) showed oestrus during the first week after weaning. The one control sow with oestrus at d 20 after weaning may have had a lactational oestrus; she was not scanned. Of the IS sows, 50% (IS19-7D; 20/40), 64% (IS19-14D; 27/42) and 61% (IS26-7D; 25/41)

Discussion

Normally, sows do not experience lactational ovulation. During lactation, peripheral concentrations of LH and LH-pulsatility are suppressed due to the suckling-induced inhibition of the GnRH-pulse generator (De Rensis et al., 1993) and also to the negative energy balance of the sow during lactation (e.g. Quesnel et al., 1998, Van Den Brand et al., 2000a), which inhibit follicle growth and ovulation. Nevertheless, in the course of lactation, LH-pulsatility normally restores to some degree (Van

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