Effects of level of feeding on energy utilization by Angora goats
Tovar-Luna, I., R. Puchala, T. Sahlu, H. C. Freetly, and A. L. GoetschJournal of Animal Science 89:142-149. 2011
Twelve mature Angora does were used in a replicated 3 × 3 Latin square to determine effects of feeding level on energy utilization. Fiber growth and change in tissue (non-fiber) mass were determined in the first 4 wk of 6-wk periods, preceded by 14 or 18 d of adaptation. Determination of ME intake 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 (L, M, and H, respectively). Digestibilities and diet ME/GE were not affected by treatment with different levels of offered feed and subsequent intake near MEm. Heat energy (HE) during fasting (261, 241, and 259 kJ/kg BW0.75; SEM = 8.7) and efficiency of ME use for maintenance (71.6, 69.6, and 69.2%; SEM = 2.29) were similar among treatments, although MEm differed (P < 0.04) between M and H (365, 344, and 377 kJ/kg BW0.75 for L, M, and H%, respectively; SEM = 10.3). Tissue gain was lower (P < 0.01) for L than for the mean of M and H (-0.6, 23.7, and 29.8 g/d), although clean fiber growth only tended (P < 0.09) to differ between L and the mean of M and H (5.60, 6.57, and 7.36 g/d for L, M, and H, respectively; SEM = 0.621). Intake of ME was greater (P < 0.01) for the mean of M and H than for L (6.87, 8.22, and 8.41 MJ/d for L, M, and H, respectively). Total HE was lower (P < 0.02) for L vs. the mean of M and H and tended (P < 0.07) to be greater for H than for M (6.03, 6.31, and 6.77 MJ/d); mobilized tissue energy was low but greater (P < 0.02) for L vs. the mean of M and H (0.16, 0.01, and 0.04 MJ/d for L, M, and H, respectively). Efficiency of ME use for fiber growth was similar among treatments (17.2, 16.3, and 17.7% for L, M, and H, 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, but preferential usage was not complete possibly because energy metabolism for tissue accretion reached a plateau with the highest feeding level.
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