Calcium and phosphorus retention by the milk-fed lamb, with estimates of the endogenous losses

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Abstract
SUMMARY: The total body content of calcium and phosphorus of twenty-seven male cross-bred lambs was determined, after the lambs had suckled ewes at pasture for between 2 and 5d. The relationships between empty body weight and Ca and P content were described by linear regression equations. The comparative slaughter method was used with thirty-seven lambs, and the balance method with twenty lambs, to determine the retention of Ca and P from cow's milk by lambs given intakes of milk ranging from maintenance (or below) toad lib. The availability of Ca, calculated as true digestibility, was 88–1 %, and for P, 98–2 %. Estimates of net availability, calculated from the slopes of the regressions relating mineral intake to mineral apparently absorbed, were somewhat higher and close to 100%. The net efficiencies of Ca and P retention, as estimated from the slopes of the regressions relating mineral intake to mineral retention, were also close to 100%. The balance method gave higher estimates of Ca and P retention than the comparative slaughter method. Multiple regression equations were used to describe the dependence of P retention on N and Ca retention. A low-calcium diet was given to two lambs for 20 d and the endogenous losses of Ca (and P) in the faeces and urine were determined. The total endogenous losses were 9–5 + 0–9 mg Ca (and 30–3 ± 1–4 mg P) per kg live weight d, of which the urinary losses were 0–5 mg Ca (and 27–9 mg P). Requirements for Ca, calculated for the milk-fed lamb at live weights of 5 and 10 kg, were somewhat lower than those recommended by the Agricultural Research Council (1965), but P requirements were in close agreement.
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