Effect of Lactation Length and Fasting on Various Reproductive Phenomena of Sows1

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Abstract
One-hundred-seven Duroc sows were used to determine the effects of lactation length and postweaning fast on reproductive performance of weaned sows. The study involved lactation lengths of 21 or 30 days integrated with fasting periods of either 0, 2, 3 or 4 days. Effects of treatments on interval to estrus after weaning, number of corpora lutea and number of normal embryos present at day 25 of gestation, number of pigs born and number of pigs born alive per sow were determined. Within lactation group, length of fasting did not alter interval from weaning to estrus. Sows lactating 30 days returned to estrus in a shorter (P<.01) interval than did sows lactating 21 days (5.0 vs 8.2 days). Ovulation rate was reduced (P<.05) when sows were fasted 4 days after a 30-day lactation. Number of normal embryos was not affected by lactation length or fasting. Percentage embryo survival was not affected by fasting; however, sows lactating 30 days had better embryo survival, 79.0 vs 70.7%, when compared to sows lactating 21 days. Number of pigs born and number of pigs born alive were increased (P<.05) when sows lactated 30 days as opposed to 21 days. Fasting, after a 30-day lactation, significantly reduced the number of pigs born and number of pigs born alive. It would appear that postweaning fasting has no beneficial effect on ovulation rate, number of total embryos or percentage embryo survival, nor does it reduce the interval to first estrus after weaning. Also, 30-day lactation lengths resulted in improved sow performance in the subsequent gestation. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.