Maternal heat stress reduces body and organ growth in calves: Relationship to immune status

Graphical Abstract Summary: Following in utero heat stress in late gestation, calves have lower circulating immunoglobulin concentrations relative to calves gestated in dams that received heat stress abatement. As illustrated in the top panel, IgG is lower from the first day of life and that reduction persists through the first month of life, which is a challenge to calf health. Total IgG ingested from colostrum did not differ, indicating that the calf's capacity for absorption of IgG was compromised. Uptake of IgG in the first days of life is associated with turnover (i.e., apoptosis) of the initial population of enterocytes in the small intestine, which are replaced by enterocytes that form tight junctions and limit movement of large molecules such as IgG. We tested the hypothesis that in utero heat stress increased the rate of enterocyte turnover thereby reducing the capacity for IgG uptake from colostrum. The lower panel illustrates the relative acceleration of enterocyte apoptosis, consistent with more rapid closure of the gut and reduced passive transfer. AEA = apparent efficiency of absorption.