CASE STUDY: Effect of Supplemental β-Carotene on Yield of Milk and Milk Components and on Reproduction of Dairy Cows

A well-managed, high-producing commercial dairy herd was used to test the impact of supplementing β-carotene (425 mg/d per cow) to lactating multiparous Holstein cows with normally low serum β-carotene (<3 µg/mL). Milk production was not affected by treatment (43.83 and 43.65 kg/d for the β-carotene and control diets). There was no difference because of treatment in overall 3.5% FCM (43.23 vs. 42.24 kg/d for the β-carotene and control diets) but early-lactation cows (0 to 100 DIM) and mature cows (3+ lactation) tended to produce more 3.5% FCM when supplemented with β-carotene (P < 0.10). Milk fat percentage was higher (P < 0.05) with supplemental β-carotene (3.28 and 3.18% for β-carotene and control cows), especially in early-lactation cows and mature cows. Overall milk fat yield (kg/d) was unaffected by treatment but early-lactation and mature cows supplemented with β-carotene tended to produce more milk fat than control cows. Milk true protein percentage and yield were not affected by treatment. Milk urea N levels were higher for cows supplemented with β-carotene (16.06 vs. 15.72 mg/dL for β-carotene-supplemented and control cows; P < 0.05). Somatic cell count was not affected by treatment. Overall pregnancy rate was unaffected by treatment, but after 105 d of β-carotene supplementation, pregnancy rate was 22% for β-carotene-supplemented cows compared with 11% for control cows. β-Carotene supplementation increased percentage of milk fat and tended to increase 3.5% FCM and milk fat yield in early-lactation and mature cows.