Effects of acclimatization on energy expenditure by meat goats

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 5.6m×3.1m 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 year period based on EE:heart rate (HR) of each doeling. Climate variables were averaged over 2, 4, 6, and 8 weeks preceding EE measurement. Doelings were fed to meet the maintenance energy requirement (MEm). Average mean, low, and high values during the 2 weeks 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 year 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×period interaction. Nonetheless, the effect of RH in models including genotype, period, and genotype×periodwas significant for 2, 4, 6, and 8weeks (P < 0.01). The R2 of linear regressions of EEdiff against RHwas slightly greater for 2 and 4 vs. 6 and 8weeks (0.11, 0.10, 0.08, and 0.07, respectively); regression coefficients for 2 and 4 weeks 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 BW0.75 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.