Abstract
Abstract Selection for genotypes of pigs with increased growth rate, larger mature size, reduced levels of body fatness and greater prolificacy has resulted in a need to reassess nutritional requirements of primiparous sows, there being a substantial effect on all phases of the reproductive cycle. These effects are greater than in the multiparous sow, probably because of marked differences in growth ambitions which create a conflict of interest for the metabolism of the immature breeding sow. Where feeding is adequate and conception not premature, there is no evidence to support special increases or decreases in nutrient supply to enhance ovulation rate, embryo survival, or late gestation foetal growth. There is no proven influence of gestation feed intake on lactation feed intake independent of body fatness at parturition. Lactation feed intake limitation renders the primiparous sow prone to severe maternal lipid and protein losses required in the support of lactation. Conventional intakes are usually below those required daily to attain energy and nitrogen balance. Excessive negative balances will utilise available labile body lipid and body protein, and reproductive efficacy is compromised. Overall, it would appear unwise to allow P2 backfat depth to fall below 14 mm or to rise above 25 mm (lipid:protein ratio > 1:1 and
Published Version
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