Effects of moderate feed restriction on energy expenditure by 2-year-old crossbred Boer goats
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Fourteen Boer (75%) Spanish wether goats (51 1.8 kg BW and 23 months of age) were used to determine effects of a moderate degree of nutrient restriction on heat production or energy expenditure (EE). The experiment consisted of a 26-day period (P1) followed by one of 50 days (P2). Wethers were fasted on the final 4 days of each period, with gas exchange measured on the last 2 days. Fasting was preceded by collection of feces and urine for 7 days, with the final 2 days for gas exchange. All wethers were fed a 65% 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); eight wethers also were fed at this level for 15 days but then had ME intake sequentially reduced by approximately 10 and 20% for 10 and 21 days, respectively (P2-80 treatment). This schedule was chosen because of a similar one used in a separate experiment to compare different goat genotypes and diet nutritive values. 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 EE was lowest (P < 0.05) for P2-80 (495, 505, 467, and 406 kJ/kg BW0.75), whereas EE 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 for P1-100, P1-80, P2-100, and P2-80, respectively), and when P2 data were analyzed separately MEm was lower (P < 0.10; 374 kJ/kg BW0.75 versus 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 versus 0.625). In conclusion, moderate feed intake restriction impacted EE and MEm by mature meat goats largely via decreasing EE that is responsive to nutrient intake rather than EE of basal metabolism when fasting. 2006 Elsevier B.V. All rights reserved.
