Cumulative effect of different acute stressors on physiological and hormonal responses and milk yield in lactating Saanen goats

Abstract

This study addresses the hypothesis that acute stress can cumulatively cause a decrease in milk yield in Saanen goats. In fact, dairy animals are subject to several environmental and management challenges that may cause acute stress during the same lactation. However, the cumulative effect of acute stress on milk yield remains unclear. Thus, the objective of this study was to evaluate the effects of different acute stressors on milk yield and milk quality in goats. Thirty Saanen goats were either maintained on their usual routine and comfort conditions (control group) or subjected to different environmental stressors (heat stress, adrenocorticotropic hormone [ACTH] administration, hoof care, and rain). These stressful challenges were performed sequentially, one challenge per day, on four consecutive days to evaluate the influence of the challenge on milk yield and milk quality. The acute stress imposed on goats caused significant changes in respiratory rate, rectal temperature, cortisol, insulin, triiodothyronine, insulin-like growth factor 1, and glucose concentrations when compared to the control group. Although these acute-stress-triggered physiological responses are fundamental to restoring homeostasis, the cumulative effects of different imposed challenges caused a change in hormone release, an increase in somatic cell count (SCC), and a decrease in milk yield. In this context, the results of this study indicate that farmers should avoid concurrently subjecting goats to management and environmental challenges that can induce acute stress because these stressors have a negative and cumulative impact on SCC and milk yield.