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The phosphorus requirement of pregnant sheep
Published online by Cambridge University Press: 27 March 2009
Summary
Thirty-eight mature Scottish Blackface sheep were mated at pasture and 32 brought indoors when 3–4 weeks pregnant. Eight were killed at this stage as controls (CI). The remaining 24 were offered a basal hay ration (200 g/head/day) supplemented with a semi-purified diet containing 84 g crude protein/kg and either 1·5 (P1), 2·8 (P2) or 9·3 (P3) g P/kg dry matter. The rate of feeding of the supplement allowed a mean daily P intake (g/day) in groups P1, P2 and P3 of 1·1, 1·6 and 4·7 and 1·6, 2·5 and 7·9 during weeks 4–15 and 16–21 of pregnancy, respectively. Six well-nourished sheep, fed conventionally, provided control ewes and lambs.
Balance trials were conducted on four sheep from each of groups P1 P2 and P3 during weeks 9–10, 14–15 and 19–20 of pregnancy. All sheep were slaughtered at parturition and selected bones of ewes and lambs removed for histological and chemical examinations. Whole body fat, nitrogen, Ca and P contents of the ewes and mineral content of the lambs were determined.
The faecal P excretion of the P1 sheep ranged from 10·8 to 19·1 mg/kg body weight/ day; urinary P excretion ranged from 0·7 to 2·9 mg/kg body weight/day in early and mid-pregnancy and from 1·0 to 8·1 mg/kg body weight/day in late pregnancy. It is suggested that on this evidence the minimum net faecal and urinary endogenous P loss can be no greater than about 13·5 mg/kg body weight/day. Carcass analysis and bone histology and chemical composition confirmed that the P requirement of pregnant ewes is much smaller than has been generally assumed.
It is suggested that for a 50-kg ewe carrying twins the P requirement increases from an average of 1·1 g/day during the first to about 2·5 g/day during the last month of pregnancy.
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