Effects of Prepartum Supplementation and Yeast Fermentation Products on the Progesterone‐Modulated Transfer of Passive Immunity in <i>Bos indicus</i> Cows

Inadequate colostrum intake increases risks of calf morbidity and mortality. This study investigated the effects of prepartum and early postpartum supplementation and yeast fermentation products on late-pregnant Bos indicus cows, and the role of progesterone in mediating passive immunity transfer. Thirty-six Brahman cows were allocated to three treatment groups: Control (ad libitum Rhodes grass hay), Supp (Control plus 1 kg/day supplement) and SCFP (Supp plus 14 g/day Saccharomyces cerevisiae fermentation products). Treatments started 30 days before the expected calving date and continued until 14 days postpartum. Cow plasma samples were collected three times a week (Monday, Wednesday and Friday), and modelled to reflect daily changes in progesterone leading up to calving. Calf plasma samples were taken twice within the first 5 days of life, and colostrum samples were collected 6-12 h post-calving. Live weights of both cows and calves were measured three times a week for 14 days before and after calving. Data were analysed using a linear mixed-effects model, and plasma progesterone concentration was assessed with a segmented mixed model. Supplementation (Supp vs. Control) improved cow nutritional status during the prepartum period, increasing dry matter, protein and metabolizable energy intake (p < 0.05), resulting in higher plasma urea (p < 0.01) and lower plasma non-esterified fatty acids (p < 0.01) and beta-hydroxybutyrate (p = 0.01) during the last week before calving. Supplementation reduced plasma progesterone concentration during the 3 days before calving (p < 0.05), which was associated with enhanced transfer of maternal IgG into colostrum (p = 0.03) and improved calf growth (p = 0.01). Yeast fermentation products (SCFP) further improved passive immunity transfer to calves (p = 0.02). These findings highlight the effectiveness of short-term prepartum supplementation, especially with yeast fermentation products, and the important role of progesterone in mediating passive immunity transfer.