The effect of supplementary minerals, retinol and α -tocopherol on the vitamin status and productivity of pregnant Merino ewes

Abstract

Four hundred and twenty Merino ewes were divided into four treatment groups: control (NaCl at 175 g head-1 week-1 ), vitamins (salt containing 0.24 g/kg retinol plus 12 g/kg ß-tocopherol), minerals (a multi-element mineral mix (Siromin ) at 175 g head-1 week-1) and vitamins plus minerals (mineral mix plus vitamins) in a two by two factorial design. Treatments started in November prior to mating and finished in May 1 week prior to lambing. Measurements of vitamin status and animal productivity were made on ewes and foetal and weanling lambs. Compared with salt, the mineral mix increased ewe body weight by up to 3% ( P < 0.05), annual wool growth by 4.4% ( P < 0.001) and birth and weaning weights of single lambs by 7.3% ( P < 0.01) and 3.7% (P < 0.05) respectively. Since ewes had been given selenium and cobalt bullets at weaning, the results suggest either that the bullets do not offer protection for the lifetime of the ewe and that additional bulleting is warranted, or that other minerals are limiting production. As pastures dried off, the concentrations of ß-tocopherol and G-carotene fell and this was reflected in a decline in the concentrations of ß-tocopherol and retinol in liver. However, the liver stores at the beginning of summer were sufficient to prevent the appearance of clinical signs of vitamin deficiency. Vitamin supplementation significantly increased the concentration of vitamins in the plasma and liver of ewes ( P < 0.001)) but it had no significant effect on ewe reproductive performance or on ewe or lamb body weights or wool growth. Vitamin supplements increased the concentrations of retinol and ß-tocopherol in the liver of foetal lambs, but even with supplements the levels remained well below normal adult reference values.