Plasma concentrations of LH, prolactin, oestradiol-17 and progesterone in sows weaned after lactation for 10 or 35 days

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Abstract
Piglets were weaned from multiparous sows at 10 days (group E; n = 7) or 35 days (group C; n = 8) of lactation. Blood samples were collected at 8-h intervals from the day before weaning (day - 1) until and including the day of 1st mating, then once daily until 10 days post coitum. Additionally, 5 sows in each group were sampled at 30-min intervals for 12 h on days-1,0 and 1, then at 30-min intervals for 6 h daily until mating, finally at 30-min intervals for 2 h daily until 5 days post coitum. group E sows had relatively longer weaning to remating intervals (8.3 .+-. 0.8 compared with 5.0 .+-. 0.7 days; P < 0.01) and tended, but not significantly, to produce smaller subsequent litters (10.2 .+-. 1.9 compared with 12.0 .+-. 0.6). Sows in group E had lower lactational and post-weaning plasma LH [luteinizing hormone] levels (P < 0.001). They also had greatly attenuated preovulatory LH rises and the area under the peak was reduced (P < 0.01 and P < 0.001, respectively). Preweaning plasma prolactin levels were higher at 9 days of lactation than at 34 days and levels in both groups dropped precipitously subsequent to piglet removal. Although peak levels of prolactin at estrus did not differ between treatments, they tended to occur before the LH peak in sows of group C and after the LH peak in group E. No treatment differences were detected in plasma levels of estradiol-17.beta. or progesterone. The poorer reproductive performance of sows after a very short lactation apparently is due, at least in part, to a reduced release of LH at the 1st post-weaning estrus.

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