THE EFFECTS OF STAGE OF PREGNANCY, MATING AT THE FIRST AND SECOND ESTRUS AFTER WEANING AND LEVEL OF FEEDING ON FETAL SURVIVAL IN SOWS

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Abstract
Three experiments were conducted to study the effect of the stage of pregnancy, mating at the first and second estrus after weaning and level of feeding on the number of fetuses and fetal survival in 125 Yorkshire and 111 Lacombe primiparous sows. In experiment 1 the sows were fed 1.36 kg of a sow ration twice daily, bred after 18 days postweaning and killed at 10, 25, 67 and 109 days of pregnancy. Sows in experiments 2 and 3 were fed 1.82 and 2.72 kg once daily and bred at the first and second estrus after weaning. In experiment 2 the sows were killed at either 10, 25, 67 or 109 days of pregnancy. In experiment 3 the sows were killed at 67 days of pregnancy. The mean number of fetuses and fetal survival percentages at the four stages of pregnancy using data from both experiments 1 and 2 were 13.1, 88.2%; 12.2, 82.6%; 10.9, 72.9%; and 11.0, 71.9%, respectively. Sows bred at the second estrus had more (P < 0.01) fetuses than sows bred at the first estrus. The increase in fetal numbers was due to an increase in both ovulation rate and fetal survival at the second estrus. The level of feeding had no direct effect on the fetal numbers, ovulation rate or fetal survival. There was an interaction (P < 0.05) between the estrus of mating and level of feeding. Sows fed 2.72 kg per day had fewer fetuses when bred at the first estrus than at the second estrus, whereas sows fed 1.82 kg per day had a similar number of fetuses when mated at the first and second estrus after weaning.

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