Different levels of response to heat stress in dairy goats

Goats are considered more tolerant to heat stress compared to dairy cows because of their greater sweating rate and lower body weight:surface ratio, allowing greater heat dissipation. Dairy goats kept under heat load in climatic chamber experienced losses in feed intake by 22-35% and produced 3-10% lower milk with reduced contents of fat, protein, and lactose. Moreover, milk of heat-stressed goats had altered coagulation properties, which could have an important impact for cheese industry. The RNA sequencing (RNAiseq) of milk cells showed that changes in milk composition were accompanied by down-regulation in the gene expression of casein, fat and lactose synthesis, and upregulation in the expression of genes related to milk cathepsins. Despite the reduction in feed intake, blood non esterified fatty acids and blood glucose did not change in heat-stressed goats. Lower insulin secretion after meals as well as muscle degradation are possible mechanisms to maintain the blood glucose levels under heat stress. Heat stress increased digestibility, which might partially compensate the reduction in feed intake. The microarray of blood cells revealed a change in the expression of genes regulating fat metabolism, which might be related to immune functions of blood cells under heat stress. In conclusion, heat stress exerts important changes in the metabolic functions, gene expression, inflammatory status, and productivityof dairy goats. Heat stress during pregnancy could permanently condition the productivity of the offspring, but this issue needs further investigation in dairy goats. (C) 2013 Elsevier B.V. All rights reserved.