Effects of Heat Exposure and Restricted Feeding on Behavior, Digestibility and Growth Hormone Secretion in Goats

  • Hirayama, Takuji (Faculty of Agriculture, University of the Ryukyus) ;
  • Katoh, Kazuo (Graduate School of Agricultural Science Tohoku University)
  • Received : 2003.10.06
  • Accepted : 2004.03.02
  • Published : 2004.05.01


Heat stress is known to affect physiological systems in goats. This study investigated changes in nutrient digestibility, behavior and growth hormone secretion among goats in a hot environment (H; 35${\pm}$ 1.2$^{\circ}C$, [RH] 80${\pm}$7.2%, 13 d), and in a thermoneutral environment (T; 20${\pm}$0.6$^{\circ}C$, [RH] 80${\pm}$3.4%, 20 d), and accompanied by the same restricted diet as provided in the hot environment. 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. CP, NDF and ADF digestibility was highest in 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. Growth hormone concentrations in T increased 4.5 h after feeding. In H, growth hormone concentrations increased 0.5 h after feeding. However, growth hormone concentrations were not changed following TR feeding. In conclusion, heat exposure in goats decreased feed intake, but increased digestibility. However, when goats in a thermoneutral environment received the same restricted feeding as they received in the hot environment, digestibility increased. 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. To maintain energy balance under a hot temperature or a restricted feeding condition, goats may control their metabolism by changing growth hormone release.


GH Secretion;Goat;Heat Stress;Feed Restriction


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