Effect of maternal heat stress in late gestation on blood hormones and metabolites of newborn calves.

Heat stress in R & D and management is often thought of as only affecting the cow and the environmental control measures put in place have as goal limitation of the effect on milk production and reproduction. However, heat stress of the mother also alters the immune function of the calf, as well as its metabolism and future lactational performance. How precisely the heat stress affects the hormonal and metabolic responses of the calf immediately after birth is still not clear. Therefore, the objective of a study by Dr J.-R. Guo and collegues was to investigate the blood profiles of hormones and metabolites of calves born to cows that were cooled or heat-stressed during the dry period. The results of the study were published in the Journal of Dairy Science, Volume 99 of 2016, page 6804 to 6807, the title being: Effect of maternal heat stress in late gestation on blood hormones and metabolites of newborn calves.

A total of 18 bull calves and 20 heifer calves were used of which half were born from heat-stressed cows and half from cooled cows. The authors collected blood samples within two hours after birth, but before colostrum feeding, and hematocrit and plasma concentrations of total protein, prolactin, insulin-like growth factor-I, insulin, glucose, non-esterified fatty acids and β-hydroxybutyrate were measured. Compared with calves from cooled cows, calves from heat-stressed cows had lower hematocrit values and tended to have lower plasma concentrations of insulin, prolactin and insulin-like growth factor-I. However, heat stress of the cow had no effect on the plasma levels of total protein, glucose, non-esterified fatty acids and β-hydroxybutyrate of the calf immediately after birth.

The results suggest that maternal heat stress desensitizes the stress response of the calf and alters the foetal development by reducing the secretion of insulin-like growth factor-I, prolactin and insulin. This is expected to have carry-over implications for growth and lactation.