Low cleavage activity of 15,15'dioxygenase to convert beta-carotene to retinal in cattle compared with goats, is associated with the yellow pigmentation of adipose tissue.

Two experiments (one with twelve heifers and the other with 14 goats) were designed to evaluate the effect of increasing dietary beta-carotene concentration on the activity of the cleaving enzyme 15,15' beta-carotene dioxygenase and the concentration of beta-carotene and retinol in selected tissues. The experiments lasted 120 days. During the first 90 days animals were offered a beta-carotene unsupplemented diet. In the following 30 days, they were distributed to one of three treatments: 0, 5.5 or 352 mg of beta-carotene/kg of dry matter intake. All animals were slaughtered at the end. In heifers the concentration of beta-carotene in plasma, reflected the level of beta-carotene fed. Goats had detectable levels of beta-carotene only on day 10 of supplementation. In the liver, beta-carotene concentrations were highest with the 352 dose in both species. Heifers had the highest concentration of beta-carotene in the adipose tissue. In bovines, no interaction between beta-carotene treatment and intestinal sampling site was found (P > 0.2) for the activity of 15,15 dioxygenase. Across beta-carotene levels, results of the enzyme assay were: 0.19, 0.32 and 0.45 nmol retinal/(mg S-9 protein/h) (P < 0.01) for 0, 5.5 and 352 mg beta-carotene.kg dry matter intake -1.d-1, respectively; across intestinal sampling sites results of the enzyme assay were 0.45, 0.43 and 0.08 nmol retinal/(mg S-9 protein/h) (P < 0.01) for duodenum, jejunum and ileum, respectively. Caprine data showed an interaction between beta-carotene treatment and intestinal sampling site (P < 0.05) for the activity of 15,15 dioxygenase. The results for treatment 0 were: 1.4, 1.4 and 0; for treatment 5.5: 1.41, 1.42 and 0.13; and for treatment 352: 1.46, 1.99 and 0.48 nmol retinal/mg S-9 protein/h for duodenum, jejunum and ileum, respectively. The lower levels of duodenal and jejunal 15,15'dioxygenase activity in cattle compared with goats, may explain the greater pigmentation of adipose tissue in the former ruminant specie.