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

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.

Effects of Restricted Feeding on Intake, Digestion, Nitrogen Balance and Metabolizable Energy in Small and Large Body Sized Sheep Breeds

“…However, Graham and Searle (1979) and Kamalzadeh (2004) reported a value of 340 kJ ME/kg 0.75 /d for Merino and Swifter sheep after a relatively severe (below maintenance) period of 3 months feed restriction. Lower values of 300 kJ ME/kg 0.75 /d after a period of weight stasis of 4 to 6 months (Graham and Searle, 1975), 275 kJ (1991), Oosting et al (1995), Hirayama and Katoh (2004) and Assoumaya et al (2009). A higher (p<0.05) digestibility of OM, GE and CP, and metabolizability occurred in feedrestricted animals compared to controls.…”

Comparative assessment of growth performance of three different indigenous goat breeds exposed to summer heat stress

“…The GH is a major peptide hormone that promotes the growth, cell multiplication and cell regeneration. It has been observed in goats that the balance between the rate of energy production and utilization determines the concentration of plasma GH (Hirayama & Katoh, ). In the current study, significantly increased GH concentration was observed in the heat stress group of all the three breeds indicating the severity of heat stress on growth performance as generally the level of plasma GH was found to be significantly increased in heat stressed animals in ruminant species (Bagath et al., ; Pulina et al., ).…”

<b>Influence of calcium salts of long chain fatty acids on the intake and digestibility of rations in female kids under heat stress

“…When this zone is exceeded, the animals show heat stress, and this can trigger their thermoregulatory mechanisms, reducing the secondary activities such as dry matter intake and animal performance. The results for water intake of goats (3.08 L day -1 ) was superior to those described by Hirayama and Katoh (2004), who observed ingestions of 2.40 L day -1 for Saanen goats, under thermal stress of 35°C (Table 4).…”

“…Baccari Junior, Gonçalves, Muniz, Polastre, & Head (1996) showed that Saanen goats subjected to temperatures of 32.5°C in climatic chamber, reduced the dry matter intake and increased the daily water consumption in the same way as Hirayama and Katoh (2004), working with animals under heat stress (35°C), who also observed an increase in the water consumption for stressed animals. One way to ensure the intake of dry matter and nutrients and ease the effects of stress on the animals outside their thermal comfort zone is to provide a diet with higher energy density and low heat increment, enabling the heat reduction generated by the fermentation of food and metabolism of tissues.…”