Effects of vitamin A supplement on milk production of cows fed low-carotene diets

Current trends in dairy cattle feeding toward higher levels of grain and corn silage signify the need for more complete information on the effects of vitamin A on lactating cows. Beef cattle feeders have confined steers and heifers in dry lots for fattening and fed high levels of concentrates with corn silage. Hay was often limited or of low vitamin A quality. These cattle have occasionally shown vitamin A deficiencies after a short time in the feedlot even though they had been raised on pasture. Feed efficiency and rates of gains have been improved after the addition of vitamin A supplements (9, 39). The requirement of dairy cattle for vitamin A in reproduction and growth has been well demonstrated (33). The role of vitamin A in lactation has not been clearly elucidated. If a high level of vitamin A in the diet or in the body is an important factor in lactation at above average production levels, evidence supporting the fact should be produced in modern dairies. Grains and roughages stored for a long period will provide only a fraction of the carotene usually fed to cows under grazing management. This investigation was conducted to determine the effect on milk production of cows fed low levels of carotene and vitamin A supplementation. Calf mortality, liver vitamin A stores, and blood status of carotene and vitamin A were also observed.