Pre-intestinal stability of beta-carotene in ruminants.

The stability of beta-carotene in the rumen contents of cows, calves and sheep was investigated in vitro and in vivo. Incubation tests with rumen liquor consistently showed that carotene was relatively stable, less than 10% losses being found under a wide variety of incubation conditions and with different sources of carotene. There was no relation between the small carotene losses and the extent of fatty acid hydrogenation. Rumen liquor samples taken from a fistulated cow over a 24 h period after the feeding of alfalfa meal had a nearly constant ratio of carotene to unsaponifiable matter. Carotene was injected into the rumen of a ram after surgical ligation of the pylorus. The recovery of carotene from the combined contents of the reticulo-rumen, omassum and abomasum 24 h later amounted to 89% whereas vitamin A palmitate, under the same conditions, yielded a recovery of 70%. It is concluded that little carotene is lost normally during its passage through the pre-intestinal part of the alimentary canal of ruminants.