Effects of gender and age on energy use by young Boer goats

Abstract

Boer goats (7/8 and 1/8 Spanish breed) were used to characterize effects of gender and age on the ME requirement for maintenance (MEm). There were eight animals of each gender, doelings, intact males, and wethers castrated at 2mo of age. Kids were weaned at 3.7mo and thereafter consumed a 50% concentrate pelleted diet ad libitum while in group pens at most times. Measurement periods consisted of three segments of 12, 10, and 4 days with consumption ad libitum and near MEm and while fasting, respectively. Maintenance segment measures began at 4.9, 7.8, 11.7, and 14.8 mo of age in periods 1, 2, 3, and 4, respectively. Feed intake data, feces and urine collections, and a calorimetry system were used to determine ME intake and heat energy (HE). The MEm estimate was based on fasting HE and the slope (km) of the regression of recovered energy (RE) against ME intake with intake near MEm and while fasting, and kg was RE with ad libitum intake relative to ME intake above MEm. BW (kg) during the maintenance segment was 20.6, 30.8, 46.5, and 57.1 for doelings, 25.9, 40.1, 67.3, and 76.9 for males, and 23.1, 35.1, 53.9, and 65.0 for wethers in periods 1, 2, 3, and 4, respectively (SE=1.85). km was similar among genders and periods (P>0.05%; 70.2%, 69.5%, and 69.7% for doelings, males, and wethers, respectively; SE=1.25). Fasting HE and MEm were affected by gender×period interactions (P<0.001). Fasting HE (kJ/kg BW0.75) was 277, 272, 281, and 281 for doelings, 288, 327, 334, and 398 for males, and 274, 303, 274, and 305 for wethers (SE=10.1); MEm (kJ/kg BW0.75) was 382, 390, 399, and 420 for doelings, 412, 469, 492, and 569 for males, and 384, 417, 426, and 439 for wethers in periods 1, 2, 3, and 4, respectively (SE=14.2). kg tended (P=0.067) to vary among genders (61.5%, 48.1%, and 52.7% for doelings, males, and wethers, respectively; SE=3.91). In conclusion, MEm was not greatly different between doelings and wethers and increased for both as the study progressed, whereas that for males was greater, with the difference increasing considerably as age rose.