VITAMIN A AND CAROTENE STUDIES WITH FATTENING BEEF CATTLE

Three feeding trials were conducted to study the effect of feeding various levels of vitamin A or carotene on weight gains, feed conversion and changes in liver vitamin A stores of fattening steers. The daily intake of 6,000 I.U. of vitamin A did not prevent vitamin A deficiency during a 126-day feeding period, when average initial liver vitamin A stores of the steers were 6.8 micrograms per gram of fresh liver. On the other hand, steers with liver vitamin A stores of 51.8 micrograms per gram of fresh liver, and receiving no supplemental vitamin A or carotene, showed no vitamin A deficiency symptoms and gained approximately the same as steers receiving 17,958 or 35,875 I.U. of vitamin A daily during a 133-day feeding period. Steers receiving the vitamin A-carotene free rations did not require significantly more feed per 100 pounds gain than steers receiving similar rations and supplemented with various levels of vitamin A or carotene. Initial liver vitamin A stores of 73.4 micrograms per gram of fresh liver were not maintained in fattening steers receiving 72,100 I.U. of vitamin A daily during 112 days. Steers consuming 63.3 milligrams of B-carotene or 25,000 I.U. of vitamin A daily showed similar losses in initial liver vitamin A stores during 133 days, suggesting a conversion ratio of carotene to vitamin A of approximately 8.4:1, on a weight basis.