Low-Temperature Long-Time Pasteurization Reduces β-Carotene in Colostrum: Effects of Dietary β-Carotene Supplementation on Oxidative Stress, Fecal Microbiota, and Diarrhea in Preweaning Calves

This study comprised two related experiments. Experiment 1 evaluated the effects of low-temperature long-time pasteurization (LTLT, 63 °C for 30 min) on selected vitamins in bovine colostrum and mature milk. Experiment 2 independently evaluated the effects of dietary β-carotene supplementation on growth performance, fecal scores, oxidative status, cortisol concentrations, and fecal microbiota in preweaning calves. In Experiment 1, colostrum and mature milk were collected from four primiparous and four multiparous Holstein cows before and after LTLT. Concentrations of vitamin A, β-carotene, vitamin B1, vitamin B2, vitamin B9, and vitamin B12 were determined. In Experiment 2, 128 neonatal Holstein heifer calves were randomly assigned to a control group or a β-carotene-supplemented group (100 mg/day/calf) for 56 days. Growth performance, fecal scores, serum antioxidant indicators, cortisol concentrations, and fecal microbiota were evaluated. Colostrum contained substantially higher β-carotene concentrations than mature milk, particularly in primiparous cows (p < 0.001). LTLT reduced β-carotene concentrations by 30% in colostrum(p = 0.034) and significantly decreased vitamin B1 (p < 0.001), whereas the remaining vitamins were only minimally affected. Dietary β-carotene supplementation stabilized antioxidant enzyme activities, reduced serum malondialdehyde and cortisol concentrations (p < 0.001), decreased the occurrence of severe diarrhea (p = 0.046), increased the relative abundance of Blautia, and reduced Fusobacterium and Parabacteroides. Average daily gain did not differ between treatments (p = 0.154). Under the conditions evaluated in Experiment 1, β-carotene was the vitamin most affected by LTLT in colostrum. In the separate feeding experiment, dietary β-carotene supplementation affected several antioxidant indicators, reduced cortisol concentrations and the frequency of severe diarrhea scores, and altered fecal microbial composition, but did not affect average daily gain.