Delay in Progesterone Decline Before Parturition is Connected with Failure of Passive Immune Transfer in Tropical Composite Beef Calves ^†

Abstract

A shortage of nutrients during the final period of gestation can decrease secretion of colostrum, which is critical to newborn calf survival. The physiological mechanism modulating the nutritional control of colostrum secretion is poorly understood. Because the decline in progesterone before parturition is required for lactogenesis to occur, the objective was to evaluate the correlation between prepartum progesterone in cows and plasma immunoglobulin-G1 (IgG1) concentration in neonatal calves. From 135 pregnant cows, successful data on both prepartum progesterone and calf IgG1 was collected from 59 cow/calf pairs (animal ethics approval SA2018/05/638). The cow/calf pairs were classified into three categories according to the transfer of passive immunity: low (n = 19), medium (n = 18), or high (n = 22). Plasma IgG1 was 1025, 2395, and 3347 mg/dL for the low, medium, and high groups, respectively. Plasma progesterone 1 day prepartum was 18.3, 14.2, and 12.4 nmol/L for the low, medium and high groups, respectively. This indicates that calves with failure of passive transfer were born from cows with higher prepartum progesterone, compared to calves with high IgG1 (P = 0.05). Non-linear modelling of the progesterone data indicated the moment that progesterone started to decline (change-point). Change-point was 0.8, 2.5, and 2.4 days before parturition for the low, medium, and high groups, respectively. There was a delay in progesterone decline in the Low group compared with the High group (P < 0.05). These results corroborate the hypothesis that the delay in progesterone decline before parturition is responsible for the failure of IgG1 transfer from cows to calves.