Effects of β-carotene dietary supplementation from late gestation to early lactation on vitamin A and β-carotene status, antioxidant responses, and milk composition in Holstein cows

The transition from late gestation to early lactation challenges antioxidant defense in dairy cows. Nutritional strategies that support antioxidant capacity during this period may therefore help improve metabolic adaptation and health. This study evaluated the effects of β-carotene dietary supplementation from 60 d prepartum to 90 d postpartum on milk composition, vitamin A and β-carotene status, antioxidant responses, and β-carotene oxygenase 1 (BCO1) and β-carotene oxygenase 2 (BCO2) mRNA abundance in Holstein cows. Twenty-four multiparous Holstein cows were assigned to receive 0, 0.6, 1.2, or 1.8 g/d β-carotene ( n = 6 per treatment). Dry matter intake and colostrum yield did not differ among groups. Compared with βC0, colostrum fat was higher in βC1.2 and βC1.8, while βC1.2 had the highest colostrum βC and vitamin A concentrations. Mature-milk fat, protein, total solids, and lactose remained unchanged; however, somatic cell count was lower in all supplemented groups, and milk yield and milk efficiency increased with βC dose. Mature-milk vitamin A was highest in βC1.2, while mature-milk βC was higher in all supplemented groups. Serum βC was higher in all supplemented groups and highest in βC1.2 and βC1.8, whereas serum vitamin A was unchanged. Hepatic vitamin A and βC were higher in βC1.2 and βC1.8 and highest in βC1.8. Serum total antioxidant capacity was higher in βC1.2 and βC1.8; glutathione peroxidase and superoxide dismutase were higher and inducible nitric oxide synthase was lower in all supplemented groups. Reactive oxygen species were lower in βC1.2 and βC1.8 and lowest in βC1.8, whereas total oxidant status was lower in βC0.6 and βC1.8. Glucose was higher in βC1.2 and βC1.8, insulin was lowest in βC1.2, and insulin-like growth factor 1 was highest in βC0.6. Tissue antioxidant responses were organ-dependent, but malondialdehyde was generally lower after βC supplementation. Hepatic BCO1 was higher only in βC1.8, whereas hepatic BCO2 decreased linearly; intestinal BCO1 and BCO2 responses were nonlinear. β-Carotene supplementation during the transition period may support the nutritional and antioxidant status of Holstein cows, particularly at supplementation levels of 1.2 and 1.8 g/d.