Baccari F, Johnson H D, Hahn G L
Proc Soc Exp Biol Med. 1983 Jul;173(3):312-8. doi: 10.3181/00379727-173-41648.
Five Holstein heifers, 5 months of age, were housed in the Missouri Climatic Laboratory and subjected to an experiment to measure the effects of heat stress on rates of growth, plasma triiodothyronine (T3) levels, and ability to compensate in rate of gain and thyroid function following the stress period. The experiment consisted of 3 weeks at thermoneutral (TN1), followed by 5 weeks of individually controlled heat stress conditions (32.5 to 34 degrees C) dependent on heat tolerance of individual animals. This was followed by a 4-week thermoneutral, postheat compensatory period (TN2). Average daily gains were significantly depressed during the heat stress period (HS). Following heat stress the average body weights attained the projected or expected levels within a 21- to 28-day period following return of animals to thermoneutral conditions. Ratios of feed intake/body weight (w0.75) were reduced during heat stress treatment indicating the thermal inhibition. Ratios or amount of feed intake per unit of gain were greater during HS treatment indicating less weight gain per unit of daily feed intake. Plasma T3 was reduced during heat treatment similarly to daily weight gain. Following the postheat treatment period (TN2) plasma T3 increased markedly as did daily weight gains to demonstrate strong compensatory responses in both measures. In summary, these results demonstrated parallel and positive changes of plasma T3 with daily weight gain during thermoneutral, heat, and postheat compensatory periods, and an inverse relationship of rectal temperature to weight gain and plasma T3.
五头5月龄的荷斯坦小母牛被安置在密苏里气候实验室，进行一项实验，以测量热应激对生长速率、血浆三碘甲状腺原氨酸（T3）水平的影响，以及应激期后在生长速率和甲状腺功能方面的补偿能力。实验包括3周的热中性（TN1）期，随后是5周根据个体动物耐热性进行单独控制的热应激条件（32.5至34摄氏度）。之后是4周的热中性、热应激后补偿期（TN2）。在热应激期（HS），平均日增重显著下降。热应激后，动物恢复到热中性条件后的21至28天内，平均体重达到了预计或预期水平。在热应激处理期间，采食量/体重（w0.75）的比值降低，表明存在热抑制。在热应激处理期间，每单位增重的采食量比值或数量更大，表明每单位日采食量的体重增加更少。热应激期间血浆T3与日增重一样降低。热应激后处理期（TN2）后，血浆T3显著增加，日增重也显著增加，表明这两项指标都有强烈的补偿反应。总之，这些结果表明，在热中性、热应激和热应激后补偿期，血浆T3与日增重呈平行且正向变化，直肠温度与体重增加和血浆T3呈负相关。
