Effects of oral and injected vitamin A (retinol) supplements on liver vitamin A and plasma carotenoid and cholesterol concentrations in cattle

Two experiments determined the effects of daily oral supplements of vitamin A (retinol) and injected preparations of vitamin A on liver vitamin A conc entration and plasma carotenoid (PC) concentration. Vetade is an oily injec table vitamin A preparation, while Nov-a-Vit is nit aqueous injectable vita min A preparation. Angus crossbred heifers were used in experiment 1 and An gus and Simmental crossbred steers were used in experiment 2. All cattle gr azed pasture but were given also 1 kg per head of pellets daily and vitamin A supplements were included in the pellets when required. In experiment 2, one group of heifers was given 1 x 10(6) i.u. vitamin A per head daily for 31 days, while a second group in another part of the paddock ions nor supp lemented with vitamin A. A third group of heifers grazed with this latter g roup and was injected with 2.5 x 10(6) i.u. vitamin A (Vetade) three times weekly. The oral vitamin A supplement proportionately reduced plasma and li ver carotenoid concentrations by 0.49 and 0.41 respectively, while increasi ng liver vitamin A concentration three-fold. By contrast, the Vetade failed to increase liver vitamin A concentration or to reduce liver and plasma ca rotenoid concentrations. In experiment 2, two groups of steers were injecte d twice weekly for 7 weeks with 2 x 106 i.u. vitamin A as Nov-A-Vit or as V erade. A third treatment group, grazing with these steers, received no vita min A injection, while a fourth group grazing in a separate area of the pad dock was supplemented daily with 1 x 10(6) i.u. vitamin A per head in their diet. The injection of Nov-A-Vit and the oral vitamin A supplement decreas ed PC concentration by a similar amount but the increase in liver vitamin A concentration was larger for steers injected with Nov-A-Vit. Vetade inject ions failed to increase liver vitamin A concentration and there was no decr ease in PC concentration. The plasma cholesterol concentration for the trea tment groups varied over the duration of the experiment but could not be re lated to the vitamin A treatment or to the changes in PC concentration. The se results indicate that vitamin A injections can be used to reduce PC conc entration provided they increase liver vitamin A concentration.