Investigation of seasonal variations in cow serum retinol and beta-carotene by high performance liquid chromatographic method.

1. High performance liquid chromatography (HPLC) was used to determine beta-carotene and retinol in cow serum. 2. Two groups of state and private farm cows (Groups 1 and 2) were used to assess seasonal variation when different food sources were fed to cows on serum beta-carotene and retinol concentrations. 3. Mean serum concentrations of beta-carotene and retinol from October to April in both Groups 1 and 2 cows were lower (P less than 0.05) than in the other months when the cows were fed various combination of maize silage, alfalfa and carrot residues and grass hay, respectively. 4. Mean serum beta-carotene and retinol concentrations in June and July were higher (P less than 0.05) than in other months when the cows were in pasture. 5. Mean serum beta-carotene and retinol concentrations in May, August and September were lower (P less than 0.05) than in June and July and higher (P less than 0.05) than in other months when a lesser amount of green pasture was available to the cows. 6. There was a seasonal variation (P less than 0.05) in serum beta-carotene and retinol concentrations. When the carotene intake is very high, conversion of beta-carotene to retinol decreases. Mean monthly serum beta-carotene and retinol concentrations showed that combination of alfalfa hay and maize silage, and grass hay and carrot residues can maintain adequate serum beta-carotene and retinol concentrations during the dry season.