Animal Behavior & Well Being

Fourteen Boer (75%) x Spanish wether goats (51 ± 1.8 kg BW and 23 mo of age) were used to determine effects of a moderate degree of nutrient restriction on heat production (HP). The experiment consisted of a 26-d period (P1) followed by one of 46 d (P2). Wethers were fasted on the final 4 d of each period, with gas exchange measured on the last 2 d. Fasting was preceded by collection of feces and urine for 7 d, with the final 2 d for gas exchange. All wethers were fed a 60% concentrate diet at a level of intake near maintenance in P1 (P1-100 and P1-80 treatments). In P2, six wethers continued on this level of intake (P2-100 treatment); to mimic procedures in a separate experiment, eight wethers also continued at this level for 15 d but then had ME intake sequentially reduced by 10 and 20% for 10 and 21 d, respectively (P2-80 treatment). Dietary ME concentration in period 2 was greater (P < 0.05) for 80 than for 100 treatments (13.2 vs 12.4 MJ/kg DM). Intake of ME was lowest (P < 0.05) for P2-80 (529, 535, 552 and 474 kJ/kg BW0.75 (fasted) for P1-100, P1-80, P2-100, and P2-80, respectively). Fed HP was lowest (P < 0.05) for P2-80 (495, 505, 467, and 406 kJ/kg BW0.75), whereas that while fasting was similar among treatments (287, 279, 273, and 253 kJ/kg BW0.75 for P1-100, P1-80, P2-100, and P2-80, respectively). The ME requirement for maintenance (MEm) was greater (P < 0.05) in P1 than P2 (477, 487, 421, and 376 kJ/kg BW0.75), and when analyzed for P2 separately MEm was lower (P < 0.10; 374 vs 425 kJ/kg BW0.75) and the efficiency of ME use for maintenance was greater (P < 0.08) for P2-80 than for P2-100 (0.689 vs 0.625). In conclusion, moderate feed intake restriction impacted HP by mature meat goats largely via decreasing that associated with or responsive to nutrient intake or workload rather than physiological processes responsible for fasting HP, with a magnitude of change in MEm 65% of that in ME intake. Supported by USDA Project No. 00-38814-9500.