Stimulation of Estrus and Ovulation in Lactating Sows

Abstract Text: Practical methods for inducing estrus and conception in lactating sows have been a goal of researchers since the 1950’s.  In this experiment, we used a modified litter separation and boar exposure treatment for inducing lactational estrus. A total of 36 multiparous and 17 primiparous sows were assigned to either control (n=25) or altered sucking (ALT; n=28) treatments.  Litter size was equalized within parity (multiparous or primiparous) to 11.6 ± 1.2 pigs at d 2 post-farrowing. At d 18 of lactation (this and subsequent days are averages), sows were allotted to treatments and the ALT sows were penned in adjacent pairs within parity so that pigs could be moved between litters by temporarily lifting the divider between the two litters. On d 18, all but the 5 lightest pigs from each ALT litter were weaned. The 5 lightest pigs for each pair of litters formed a combined litter that nursed each sow of the pair 12 h/d from d 18 to 25. Therefore, pigs had nursing access 24 h/d, but each ALT sow was only suckled 12 h/d. Boar exposure was provided only to ALT sows for 15 min/d by moving sows to a pen outside the farrowing room. Control and ALT sows were weaned at d 21 and d 25, respectively. Sow weights and litter performance during lactation were similar between treatments, although ALT sows had 16% greater total feed intake (138 vs. 116 kg; P<0.01) due to the 4 d extended lactation period. Primiparous sows lost a greater percentage (7.4 vs. 3.4%) of BW and consumed less feed (P<0.01) than multiparous sows. A total of 26 ALT sows (93%) were detected in estrus and inseminated in lactation. Although the interval from initiating ALT to estrus was greater (P<0.001) than the wean-to-estrus interval for controls, ALT sows were in estrus earlier post-farrowing (23.0 vs. 24.6 d; P<0.001) than controls. Primiparous sows exhibited estrus later (5.4 vs. 3.8 d; P<0.01) than multiparous sows for both treatments. Pregnancy rate and subsequent reproductive performance were similar between treatments. The ALT treatment is unique in that nursing is by a combined litter of light-weight pigs. Whether this contributed to the high incidence of lactational estrus is not known; however our results provide evidence that the ALT treatment can induce estrus in lactating sows at rates comparable to conventionally weaned sows and with similar reproductive performance.

Keywords: boar exposure, lactational estrus, split weaning