The effect of nutrition on the reproductive performance of first-litter sows 2. Protein and energy intakes during lactation

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Abstract
A factorial experiment involving high (53·1 to 59·5 MJ) and low (25·4 to 27·1 MJ) daily intakes of digestible energy, and high (550 to 745 g) and low (302 to 318 g) daily intakes of crude protein during lactation, was conducted with 68 first-litter sows. Average lactation length was 32 days, and average backfat changes during lactation were +0·3, −1·4, −7·2 and −5·4 mm for the high energy/high protein, high energy/low protein, low energy/high protein and low energy/low protein combinations, respectively. The corresponding mean live-weight losses during lactation were 3·9, 32·5, 29·8 and 35·8 kg. Within 8 days of weaning, more sows receiving high intakes of both energy and protein during lactation exhibited oestrus (0·88 v. 0·53, x2 = 6·7, P < 0·01) than sows whose energy and/or protein intake throughout lactation had been restricted. Nitrogen balances of sows were determined between 18 and 22 days after farrowing. Sows receiving high intakes of both energy and protein during lactation were in positive nitrogen balance, whereas the nitrogen balances of sows on the other three dietary treatments during lactation were similar to each other but negative. Ovulation rate, subsequent litter size and embryo mortality were not significantly affected by energy or protein intake during lactation.