Bovine vitamin A and beta-carotene intake and lactational status. 2. Responsiveness of mitogen-stimulated peripheral blood lymphocytes to vitamin A and beta-carotene challenge in vitro.

The interaction of dietary vitamin A and beta-carotene with lactational status on the in vitro proliferation of mitogen-induced peripheral blood lymphocytes was studied. Cows were fed (IU/cow per d) 1) 53,000 IU vitamin A, 2) 213,000 IU vitamin A, or 3) 53,000 IU vitamin A plus 400 mg beta-carotene from 6 wk before to 2 wk after dry off. Lymphocytes were incubated with retinol, retinoic acid, or beta-carotene. Concanavalin A-induced blastogenesis was inhibited by 10(-6) M retinol and 10(-8) M retinoic acid in cows fed 53,000 IU vitamin A before dry off. In contrast, 10(-7) M retinol and 10(-7) M retinoic acid stimulated Concanavalin A-induced blastogenesis for cows fed vitamin A plus beta-carotene before dry off. After dry off, retinol and retinoic acid did not affect Concanavalin A-induced blastogenesis in all treatment groups. In vitro, 10(-5) M beta-carotene inhibited Concanavalin A-induced blastogenesis before and after dry off in all treatment groups. Blastogenesis in the absence of mitogen stimulation or induced by lipopolysaccharide was inhibited by all vitamins before and after dry off in all treatment groups. These data indicate that vitamin A and beta-carotene supplementation interact with lactational status to influence the responsiveness of bovine blood lymphocytes to vitamin challenge in vitro.