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

Takuji Hirayama,Kazuo Katoh

doi:10.5713/ajas.2004.655

Abstract

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±1.2°C, (RH) 80±7.2%, 13 d), and in a thermoneutral environment (T; 20±0.6°C, (RH) 80±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. (Asian-Aust. J. Anim. Sci. 2004. Vol 17, No. 5 : 655-658)

Highlights

To maintain body homeostasis, domestic animals respond to hot environments in various ways, such as changes in rectal temperature and respiration rate (Sano et al, 1985)
The extension of eating time in H might have been caused by a decrease in the bolus size of each feeding, which would reduce the level of feed intake
Such decreases might have been occurred as part of the control of calorigenesis in order to maintain body homeostasis

Summary

Introduction

Domestic animals respond to hot environments in various ways, such as changes in rectal temperature and respiration rate (Sano et al, 1985). It is generally true that when intake down, digestibility increases irrespecti ve of the animal’s energy status. This in because the digesta passage rate slows down and gives gut microbes and enzymes more time to act on the feed. Animal production, such as milk yield and daily gain, generally stagnates during heat stress (McGuire et al, 1989; Knapp and Grummer, 1991).

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