Effects of level of feeding on energy utilization by Angora goats
I. Tovar-Luna, R. Puchala, T. Sahlu, H. C. Freetly, and A. L. GoetschProceedings of the 10th International Conference on Goats. Number 102-3. International Goat Association. 2010
Twelve mature Angora does were used in a replicated 3 × 3 Latin square to determine effects of feeding level on energy utilization. Fiber growth was measured in the first 4 wk of 6-wk periods, preceded by 2 wk of adaptation. Metabolizability and gas exchange measures occurred in wk 4, followed by feeding near maintenance then fasting in wk 5 and 6 to determine the ME requirement for maintenance (MEm). A 60% concentrate diet was fed at levels to approximate 100, 125, and 150% of assumed MEm. Digestibility and metabolizability were not affected by treatment with different levels of offered feed and subsequent intake near MEm. Energy expenditure (EE) during fasting (261, 241, and 259 kJ/kg BW0.75), efficiency of ME use for maintenance (71.6, 69.6, and 69.2%), and MEm (365, 344, and 377 kJ/kg BW0.75 for 100, 125, and 150%, respectively) were similar among treatments. Tissue (non-fiber) gain was lowest among treatments (P < 0.05) for 100% (-0.6, 23.7, and 29.8 g/d), although clean fiber growth only tended to increase with increasing level of feeding (5.60, 6.57, and 7.36 g/d for 100, 125, and 150%, respectively). Intake of ME was greater (P < 0.05) for 125 and 150 than for 100% (6.87, 8.22, and 8.41 MJ/d for 100, 125, and 150%, respectively). Total EE was greater for 150 vs. 100 (P < 0.05) and 125% (P < 0.07; 6.03, 6.31, and 6.77 MJ/d), and mobilized tissue energy was low but greater (P < 0.05) for 100 vs. 125 (P < 0.05) and 150% (P < 0.07; 0.16, 0.01, and 0.04 MJ/d for 100, 125, and 150%, respectively). Efficiency of ME use for fiber growth was similar among treatments (17.2, 16.3, and 17.7% for 100, 125, and 150%, respectively; SEM = 1.61). In conclusion, efficiency of ME use for fiber growth was similar to the NRC recommendation regardless of feeding level, although MEm was lower perhaps because of experimental conditions employed. Energy appeared partitioned to fiber growth, although preferential usage was not complete possibly because energy metabolism for tissue and fiber accretion reached a plateau eliciting increased feed refusal.
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