Effects of dietary deficiencies of energy, protein and calcium on the pregnant ewe. II. Body composition and mineral content of the lamb

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Abstract
SUMMARY The effects of low protein and low Ca intakes during pregnancy on lamb composition and mineral contents have been investigated. Twenty-eight 6½-year-old Blackface ewes were used in a 2 × 2 experiment in which semi-purified diets containing 11·8 and 6·0% crude protein and 1·2 and 0·11 % Ca in the dry matter were offered to maintain constant levels of non-esterified fatty acids (NEFA) and ketone bodies in the plasma, comparable to those found in hill sheep in winter. A further group, control, were fed a conventional diet containing adequate crude protein and Ca to maintain NEFA and ketone body levels typical of well-nourished sheep. The lambs were killed at birth and whole body fat, moisture, nitrogen, Ca, P, Mg, Na and K contents determined. Further data was obtained on the brain, liver and semitendinosus muscle. Within the context of the experiment the most important factor in determining the mineral content of the lambs was the protein intake of the ewe, mainly due to its effect on lamb body weight. The mean Ca content of lambs from the control ewes was 47·8 g. By comparison that of lambs from the high and low protein groups was reduced by 4·9 and 12·9 g respectively. Calcium intakes as low as 27 mg/kg ewe body weight/day had no significant effect on lamb birth weight or mineral composition. The mean concentrations (g/kg) of minerals in the fat-free bodies of the lambs ranged from 12·1 to 14·6 for Ca, 6·6 to 7·4 for P, 0·49 to 006 for Mg and from 1·9 to 1·6 for K in the control and double deficiency groups respectively. It was concluded that these changes in lamb composition could be interpreted according to classical studies on the influence of undernutrition on the relative growth and development of animal tissues. The livers of the lambs, although significantly reduced in weight by the protein deficiency showed no evidence of being relatively more severely affected than muscle tissue.