Effects of acclimatization on energy expenditure by different goat genotypes

Five Balady and five Shami (Damascus) intact male goats, approximately 1.5 yr of age, were individually housed and used to determine effects of ambient temperature (Ta), relative humidity (RH), and temperature-humidity index (THI) on energy expenditure (EE). Average mean, low, and high values in 2-wk periods throughout the year were 22.5, 14.9, and 28.5 °C for Ta and 61.0, 49.6, and 68.5% for RH, respectively. Animal measurements occurred monthly from December, 2006 through October, 2007. Animals were fed alfalfa hay to meet the maintenance energy requirement. Because BW was relatively constant throughout the experiment, EE was considered equal to metabolizable energy (ME) intake. In January, April, July, and October, the day of measuring heart rate (HR) occurred within a 7-day period when bucks were housed in metabolism crates for total collection of feces and urine. Individual EE to HR ratio was estimated at those times and used to predict EE throughout the year based on HR. EE in kJ/kg BW0.75 was greater for Shami than for Balady goats in January, July, and October (P < 0.05), for Balady ranked (P < 0.05) July and October < January and April, and for Shami ranked (P < 0.05) January, April, and July > October. EE:HR was greatest among times (P < 0.05) in April and greater (P < 0.05) for Shami vs. Balady. Digestibilities of DM and energy were slightly greater for Shami than for Balady (P < 0.05). For monthly measures, rectal temperature, blood hemoglobin oxygen saturation, and HR were similar between breeds. HR differed among months, with means ranging from 57.0 to 77.6 bpm. There were large differences among months in the difference between EE at particular measurement daily times and the average (EEdiff). No climate measure in the preceding 2 or 4 wk was correlated with EE or EEdiff (P > 0.10). The same was true for correlations based on all data of EEdiff and the full-day measurement of climate conditions in the month preceding HR measurement. However, when correlations were conducted separately for each genotype, some relationships for Balady goats were significant while those for Shami goats were nonsignificant. A regression of EEdiff of Balady goats against mean Ta and THI on the preceding HR measurement day revealed a coefficient of 4.17 or 2.78 kJ/kg BW0.75 per 1 °C or THI unit, respectively. In conclusion, EE of Balady goats appears sensitive to climate conditions, whereas that of Shami goats is not or at least is relatively less impacted. With hot conditions, Balady goats have an advantage in a decreased ME requirement for maintenance and with low Ta, Balady goats have an increased requirement.