Low cleavage activity of 15,15'dioxygenase to convert β-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 β-carotene concentration on the activity of the cleaving enzyme 15,15'β-carotene dioxygenase and the concentration of β-carotene and retinol in selected tissues. The experiments lasted 120 days. During the first 90 days animals were offered a β-carotene unsupplemented diet. In the following 30 days, they were distributed to one of three treatments: 0, 5.5 or 352 mg of β-carotene/kg of dry matter intake. All animals were slaughtered at the end. In heifers the concentration of β-carotene in plasma, reflected the level of β-carotene fed. Goats had detectable levels of β-carotene only on day 10 of supplementation. In the liver, β-carotene concentrations were highest with the 352 dose in both species. Heifers had the highest concentration of β-carotene in the adipose tissue. In bovines, no interaction between β-carotene treatment and intestinal sampling site was found (P > 0.2) for the activity of 15,15 dioxygenase. Across β-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 β-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 β-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.