7Warner, R. L., G. E. Mitchell, J r., C. O. Little, and N.E. Alderson. Pre-intestinal disappearance of vitamin A in steers led different levels of com. Internationl. l.VitaminResearch 1970,40: 585- 588.
8Rode,L.M. ,T.A.McAllister. Microbial degradation of vitaminAin tureen fluid from steersfed concentrate, hay or stram diets. Can. J. Anim. Sic. 1990,70: 227 - 233.
9Fernandez SC, Budowski Pet al. Pre-intestinal stability of beta-carotene in ruminants.Int J Vitam Nutr Res. 1976,46(4):439 - 45.
10Donoghue S. Transfer of vitamin A from intestine to plasma in lambs fed low and high intakes of vitamin A. J Nutr. 1983,113(11): 2197 - 2204.