The dietary requirements of calcium and phosphorus for growing lambs

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Abstract
Groups of wether lambs were fed on four concentrate diets, from a live weight (LW) of about 25 kg until they had grown to about 50 kg, when they were killed, minced and analysed. A fifth group was killed at the start of the trial to provide data on their initial composition. The dietary treatments were identical except in their concentrations of calcium (Ca) and phosphorus (P) and supplied, with some approximations: (A) 0·75 times the requirements for Ca and P estimated according to the recommendations of the AFRC Technical Committee on Responses to Nutrients (TCORN, 1990); (B) a close match to the estimated requirements for both elements; (C) 1·5 times the estimated requirements for both elements; (D) 1·5 times the Ca requirement and 0·75 times the P requirement.The retentions of Ca and P in the lambs were closely similar with diets B and C (6·8 and 7·3 g Ca per kg LW and 4·1 and 4·5 g P per kg LW) and significantly lower with diet A (4·8 g Ca and 3·0 g P per kg LW) and diet D (5·0 g Ca and 2·7 g P per kg LW). Parallel differences in response to diet were evident in the composition of the metacarpi. Plasma Ca and P concentrations showed no significant differences between the dietary treatments A, B and C, but plasma P concentrations were markedly depressed with lambs on diet D and plasma Ca concentrations were elevated in this group. Rumen P concentrations were also markedly lower in lambs on diet D and their food intakes and growth rates were lower than in lambs in other groups. The results indicate that Ca and P retentions were not increased by feeding these elements in excess of their estimated requirements and were reduced when Ca and P or P alone was reduced proportionately to about 0·75 times requirement. The data are in accord with the TCORN recommendations and suggests that they provide a satisfactory basis for defining Ca and P requirements for growing lambs.