Low utilization of carotene by sheep

The apparent digestibility of beta-carotene was determined in Awassi rams by means of balance trials. In a first series carotene was supplied per os in constant daily amounts ranging from 2.88 to 8.52 mg in the form of pelleted alfalfa meal or as a water-dispersible synthetic preparation. The supplements were given with a basal low-carotene ration composed of barley, soybean meal and straw and supplying 82 mug carotene daily. Fecal recoveries for the carotene supplements ranged from 92 to 98%, whereas the unsupplemented basal diet yielded a recovery of 28%. In a second series single doses of carotene in various carriers were introduced into the abomasum of fistulated rams. With an aqueous carotene dispersion fecal recoveries were close to 90%. When dissolved in triglycerides, carotene yielded less than 50% recovery in the feces, and free fatty acids and monoglycerides gave intermediate values. Additional tests with 3H-labelled carotene revealed that the low fecal recovery of carotene given in oil was not due to improved absorption but to degradation of carotene in the lower intestinal tract. This was confirmed by measurement of blood radioactivity. The results show that carotene from different sources and with intakes bordering on minimum requirements is poorly absorbed by sheep. It is suggested that the peculair physiology of digestion in the ruminant creates unfavorable conditions for the efficient micellar solubilization of nonpolar lipids in the upper small intestine.