The present study investigated changes in nutrient digestibility, rumen fermentation, behavior and hormone (growth hormone (GH), insulin and insulin-like growth factor-1 (IGF-1)) secretion among goats (three male goats) in a hot environment (H, 35 ± 1.2°C; relative humidity (RH), 80 ± 7.2%; 13 days), in a thermoneutral environment (T, 20 ± 0.6°C; RH, 80 ± 3.4%; 20 days), and in a thermoneutral environment accompanied by the same restricted diet as provided in the hot environment (TR, 20 ± 0.6°C; RH, 80 ± 3.4%; 20 days). The following results were obtained: rectal temperature and water intake were higher in the H treatment than in the T treatment or TR treatment, while hay consumption was lower. Crude protein, neutral detergent fiber and acid detergent fiber digestibility was highest in H treatment. The concentrations of acetic acid and butyric acid in the rumen was also highest in the H treatment. Time spent eating in the H treatment was also the highest, followed in order by T treatment and TR treatment. Ruminating time was lower in H treatment than in T treatment or TR treatment, and reposing time was highest in the TR treatment. When eating and ruminating, the amplitude values of the rumen contraction were lowest in the H treatment, as was the frequency of rumen contraction. Excretion of plastic particles was faster in T treatment and TR treatment than H treatment. Heat exposure was associated with world lowered concentrations of total volatile fatty acids and acetic acid in plasma. The plasma glucose concentration was highest in the T treatment, followed in order by TR treatment and H treatment. The plasma GH concentration was lowest in the H treatment, while the plasma insulin was highest in the H treatment. The IGF-1 concentration was highest in the H treatment, followed in order by T treatment and TR treatment. In conclusion, heat exposure in goats decreased feed intake and rumen contraction, but increased digestibility. However, when goats in a thermoneutral environment received the same restricted feeding as they received in the hot environment, digestibility increased without a change in rumen contraction. Between the H treatment and TR treatment, the changes in digestibility were accomplished by coordinate changes in hormone secretion in order to maintain body homeostasis.
- Heat stress
- Rumen contraction
ASJC Scopus subject areas
- Agricultural and Biological Sciences(all)