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 < 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 < 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 < 0.05) than in June and July and higher (P < 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 < 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.