Effects of acclimatization on energy expenditure by meat goats
Patra, A. K., R. Puchala, G. Animut, T. A. Gipson, T. Sahlu, and A. L. GoetschSmall Ruminant Research 81:42-54. 2009
Eight Spanish and eight Boer yearling doelings were used to assess relationships between energy expenditure (EE) and ambient temperature (Ta), relative humidity (RH), and temperature-humidity index (THI). Four doelings of each genotype were housed in two 5.6 x 3.1 m pens of an enclosed facility with a concrete floor without cooling and with heat provided only to prevent damage to waterers and water lines from freezing. EE was determined over 2 day periods 13 times during a 1 yr period based on EE:heart rate (HR) of each doeling. Climate variables were averaged over 2, 4, 6, and 8 wk preceding EE measurement. Doelings were fed to meet the maintenance energy requirement (MEm). Average mean, low, and high values during the 2 wk preceding EE determination were 19.9, 7.9, and 31.8?C for Ta and 53.6, 36.1, and 62.5% for RH, respectively. Neither Ta nor THI were correlated with or had significant effects in regressions to predict the difference between EE at particular measurement times and the 1 yr mean (EEdiff). Conversely, RH was correlated (P < 0.01) with EEdiff. When the 13 HR measurement times were assigned to cool and warm seasonal periods, EEdiff was affected (P < 0.01) by a genotype x period interaction. Nonetheless, the effect of RH in models including genotype, period, and genotype x period was significant for 2, 4, 6, and 8 wk (P < 0.01). The R2 of linear regressions of EEdiff against RH was slightly greater for 2 and 4 vs. 6 and 8 wk (0.11, 0.10, 0.08, and 0.07, respectively); regression coefficients for 2 and 4 wk were 1.265 and 1.163 kJ/kg BW0.75 per 1% RH, respectively. With RH of 50%, regression coefficient of 1.214 kJ/kg BWain 0.75 per 1% RH, and MEm of 390 kJ/kg BW0.75, predicted MEm is 372 and 408 kJ/kg BW0.75 at 35 and 65% RH, respectively. In conclusion, without extremes eliciting cold or heat stresses, RH appears to have a slight effect on MEm of meat goats by acclimatization in both cool and warm periods of the year.
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