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Efficiency of energy use for maintenance and gain by growing crossbred Boer and Spanish goats consuming diets differing in forage level

I. Tovar-Luna, A. L. Goetsch, R. Puchala, T. Sahlu, G. E. Carstens, H. C. Freetly, and Z.B. Johnson

Small Ruminant Research. 2006. In Press.

Eight Boer (75%) × Spanish (BS) and eight Spanish (S) wether goats (155 ± 8 days of age and 19.2 ± 2.3 kg BW, initial) were used in a replicated crossover design experiment with a 2 × 2 factorial arrangement of treatments to determine effects of genotype and diet quality on heat production with ad libitum, near maintenance and fasting levels of feed intake. Diets were 65% concentrate (CON; 15% CP, DM basis) and coarsely ground alfalfa hay (FOR; 23% CP). There were no significant interactions between genotype and diet. ME intake was similar between genotypes and greater (P < 0.05) for CON vs. FOR both when intake was ad libitum (7.60 vs. 5.43 MJ/day) and near maintenance (4.31 vs. 4.09 MJ/day). DE concentration was greater (P < 0.05) for CON than for FOR with ad libitum (74.4 vs. 55.5%) and restricted intake (77.0 vs. 59.6%). Energy expenditure (EE), determined by respiration calorimetry, at all levels of intake was similar between genotypes. EE was greater (P < 0.05) for CON than for FOR at each of the three levels of intake, ad libitum (573 and 521 kJ/kg BW0.75 while fasting), near maintenance (426 and 400 kJ/kg BW0.75) and fasting (280 and 255 kJ/kg BW0.75). Efficiencies of ME utilization for maintenance (km) and gain (kg) and the ME requirement for maintenance (MEm) were similar between genotypes. km was similar between diets (0.705 and 0.690 for CON and FOR, respectively), although kg was greater (P < 0.05) for CON than for FOR (0.603 vs. 0.387). MEm was numerically greater (P < 0.17) for CON than for FOR (407 vs. 379 kJ/kg BW0.75), which may have involved higher ME intake with CON. In conclusion, under the conditions of this experiment energy requirements and efficiency of utilization were not different between growing Boer crossbred and Spanish goats regardless of diet quality.


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