Different levels of response to heat stress in dairy goats

Goats are considered more tolerant to heat stress compared to dairy cows because of theirgreater sweating rate and lower body weight:surface ratio, allowing greater heat dissipa-tion. Dairy goats kept under heat load in climatic chamber experienced losses in feed intakeby 22–35% and produced 3–10% lower milk with reduced contents of fat, protein, and lac-tose. Moreover, milk of heat-stressed goats had altered coagulation properties, which couldhave an important impact for cheese industry. The RNA sequencing (RNA-seq) of milk cellsshowed that changes in milk composition were accompanied by down-regulation in thegene expression of casein, fat and lactose synthesis, and upregulation in the expression ofgenes related to milk cathepsins. Despite the reduction in feed intake, blood non esterifiedfatty acids and blood glucose did not change in heat-stressed goats. Lower insulin secretionafter meals as well as muscle degradation are possible mechanisms to maintain the bloodglucose levels under heat stress. Heat stress increased digestibility, which might partiallycompensate the reduction in feed intake. The microarray of blood cells revealed a change inthe expression of genes regulating fat metabolism, which might be related to immune func-tions of blood cells under heat stress. In conclusion, heat stress exerts important changesin the metabolic functions, gene expression, inflammatory status, and productivity of dairygoats. Heat stress during pregnancy could permanently condition the productivity of theoffspring, but this issue needs further investigation in dairy goats.