Effects of diet quality on energy expenditure by 20-month old Alpine, Angora, Boer and Spanish wethers
Tovar-Luna, I., A. L. Goetsch, R. Puchala, T. Sahlu, G. E. Carstens, H. C. Freetly, and Z. B. JohnsonSmall Ruminant Research 72:18-24. 2007
Six Alpine (47.7 ñ 1.36 kg initial BW), Angora (28.8 ñ 1.11 kg), Boer (87.5% Boer and 12.5% Spanish; 49.3 ñ 2.17 kg), and Spanish (38.7 ñ 0.51 kg) wethers (initial age of 19 months) were used to determine effects of genotype and diet quality on energy expenditure (EE) when fed near maintenance and fasted. The experiment consisted of four simultaneous crossovers, with 21 d for adaptation before measures. Diets were 65% concentrate (CON) or coarsely ground alfalfa hay (FOR). EE was determined from O2 consumption and production of CO2 and CH4 with a head-box respiration calorimetry system, along with urinary N excretion, over 2-day periods in fed and fasted states (4-day fast). EE was expressed on the basis of average BW during the fasted measurement period. There were only significant interactions between genotype and diet in DM and gross energy intakes, which were due to differences in magnitude. Intake of ME was similar among genotypes and slightly greater (P < 0.05) for CON than for FOR (450 vs. 424 kJ/kg BW0.75). Neither diet (373 and 371 kJ/kg BW0.75 for CON and FOR, respectively; SE = 5.9) nor genotype (377, 377, 361, and 373 kJ/ kg BW0.75 by Alpine, Angora, Boer, and Spanish, respectively; SE = 9.3) influenced fed EE (P > 0.10). Fasted EE was similar between diets but was greatest among genotypes (P < 0.05) for Alpine (251, 224, 217, and 225 kJ/ kg BW0.75 by Alpine, Angora, Boer, and Spanish, respectively; SE = 7.2), which may have been due to a greater level of activity exhibited by Alpine than other genotypes when fasted. Efficiency of utilization of ME for maintenance was similar (P > 0.10) between diets (0.685 and 0.657 for CON and FOR, respectively; SE = 0.0134). The ME requirement for maintenance was similar (P > 0.10) between diets (342 and 352 kJ/kg BW0.75 for CON and FOR, respectively; SE = 7.9) and among genotypes (353, 349, 326, and 362 kJ/kg BW0.75 for Alpine, Angora, Boer and Spanish, respectively; SE = 11.1). In summary, with a level of intake near maintenance, the maintenance energy requirement appears similar for Alpine, Angora, Boer and Spanish goats near 2 yr of age regardless of diet quality.
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