Effects of progressive feed restriction on the growth and carcass composition of pigs: comparative responses of gilts and castrates

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Abstract
SUMMARY: A barley-based diet, containing 16% protein, was given at average daily rates of 1·2–2·5 kg (16–32 MJ, metabolizable energy (ME)) to 32 female and 32 castrated male pigs during their growth from 25 to 90 kg. At high intakes there was no difference in growth rate between the sexes, but with progressive feed restriction the growth of males was more severely retarded than that of the females. Both sexes achieved their minimum feed conversion ratios at approximately 25 MJ. The reductions of fat thickness with progressive feed restriction were greater by approximately 20% in the females than in the males. The two sexes had the same mean back fat thickness when the gilts had 4·7 MJ more ME per day than the castrates. It was inferred that the energy requirement for maintenance was 15% greater in the males than in the females.