Immediate prepartum supplementation accelerates progesterone decline, boosting passive immunity transfer in tropically adapted beef cattle

Abstract

Context Poor nutrition of late-pregnant cows is highly prevalent in the dry tropics and associated with high levels of calf mortality. Aims It was hypothesised that supplementation with protein to prepartum cows would restore the normal decline in progesterone prepartum and increase the transfer of passive immunity to calves, with this being further enhanced by inclusion of yeast fermentation products. Methods In total, 84 heifers and 45 cows were selected for a completely randomised block design, with the following three dietary treatments: unsupplemented, receiving ad libitum low-protein hay only; hay supplemented with 1 kg/day of protein; and supplementation with both protein and 14 g/day of a Saccharomyces cerevisiae fermentation product. Supplementation occurred for an average of 14 days before calving. Cow plasma samples in the week before parturition, and the first plasma sample after parturition, were analysed for progesterone and metabolites. Newborn calves were weighed and blood-sampled three times per week during the first 2 weeks after birth. The first two calf plasma samples were analysed for total protein, albumin, and globulin concentrations. Data were analysed using a mixed-effects model and the decline of progesterone concentration over time was modelled using a non-linear segmented model. Key results Prepartum supplementation reduced cow liveweight loss, increased glucose, reduced fat mobilisation metabolites and tended to increase average daily weight gain of calves. Including yeast fermentation products in the supplement tended to increase the transfer of passive immunity to calves. Supplementation decreased plasma progesterone before parturition and including yeast fermentation products further advanced the initiation of progesterone decline. Conclusion Protein supplementation of protein-deficient beef cows during late pregnancy helps restore the normal decrease in progesterone before parturition. Implications This study identified a plausible hormonal mechanism explaining how poor nutrition around birth can increase calf loss, opening new possibilities for short-term diet management strategies to reduce calf mortality and improve calf health.