Effects of moderate feed restriction on energy expenditure by 2-year-old crossbred Boer goats

Abstract

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 BW 0.75 (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 BW 0.75), whereas EE while fasting was similar among treatments (287, 279, 273, and 253 kJ/kg BW 0.75 for P1-100, P1-80, P2-100, and P2-80, respectively). The ME requirement for maintenance (ME m) was greater ( P < 0.05) in P1 than P2 (477, 487, 421, and 376 kJ/kg BW 0.75 for P1-100, P1-80, P2-100, and P2-80, respectively), and when P2 data were analyzed separately ME m was lower ( P < 0.10; 374 kJ/kg BW 0.75 versus 425 kJ/kg BW 0.75) 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 ME m by mature meat goats largely via decreasing EE that is responsive to nutrient intake rather than EE of basal metabolism when fasting.