Thermal stress effects on milk yield and chemical composition and thermoregulatory responses of lactating alpines goats

[摘要] - Six Alpine goats with an average milk yield of 2.5 kg/day were randomly assigned to two groups of three and allotted to thermoneutral or heat stress conditions, for 56 days in climate chamber room. A crossover experimental design was used. The goats under heat stress were exposed to a diurnal average air temperature plus simulated solar radiation of 33. 84oC. The heat-stressed goats showed elevated respiratory frequency, respiratory minute volume, respiratory evaporation, rectal temperature and sweating rate, while the tidal volume and packed cell volume decreased. Further weight loss, decreased feed intake, and their water consumption doubled. The milk yield, the percentage of fat, protein, lactose and total solid contents decreased. The contents of chloride, calcium and phosphorus did not change. The goats mobilized the respiratory and sweating systems to lose heat to maintain homeothermy. The association between high air temperature and simulated solar radiation reduced the milk yield and the content of some milk components.

[学科分类] 兽医学

[关键词] goats;chemical composition;thermal stress;milk production     IntroduçãoDo ponto de vista bioclimático;apesar de os caprinos serem considerados animais rústicos;a associação entre elevadas temperaturas e altas umidades do ar e radiação pode acarretar alterações comportamentais e fisiológicas;como aumento da temperatura da pele;elevação da temperatura retal;aumento da freqüência respiratória;diminuição da ingestão de alimentos e redução do nível de produção (LU;1989)