Effect of initial body condition of Boer x Spanish yearling wethers and level of nutrient intake on body composition

A. T. Ngwa, L. J. Dawson, R. Puchala, G. Detweiler, R. C. Merkel, I. Tovar-Luna, T. Sahlu, C. L. Ferrell, and A. L.Goetsch

Journal of Animal Science 84(Supplement 1):325-326. 2006

Yearling Boer x Spanish wethers were used to assess effects of initial body condition and subsequent level of feed intake on body composition. Before the experiment, 27 wethers were fed to achieve high body condition score (BCS; 1 to 5, with 1 = extremely thin and 5 = extremely fat) and BW (I-F) and 27 were fed for low BCS and BW (I-T). During the experiments, I-F wethers were fed low amounts of a pelletized diet and I-T wethers received high amounts. In Exp. 1, harvest measures were determined before the experiment (wk 0) and after 12 and 24 wk, with seven animals per initial body condition and time. In Experiment 2, the other 12 animals (six per initial body condition) were used to determine energy expenditure (EE) at three times (wk 1-3, 11-13, and 22-24 for Early, Middle, and Late, respectively). As expected, there were numerous treatment x time interactions. BCS in Exp. 1 was 3.8, 3.2, 2.6, 1.9, 2.8, and 3.5 (SE = 0.11) and live BW was 53.3, 46.2, 42.4, 36.6, 40.1, and 48.2 kg (SE = 2.03) for I-F:wk 0, I-F:wk 12, I-F:wk 24, I-T:wk 0, I-T:wk 1, and I-T:wk 2, respectively. Changes in carcass mass of protein (-5.9, -5.3, 7.0, and 5.8 g/d; SE = 0.89) and fat (-1.9, 0.2, 21.4, and 26.6 g/d; SE = 2.35) were greater (P < 0.05) for I-T vs I-F, as was also true for non-carcass protein (6.1, 0.0, 14.5, and 6.3 g/d; SE = 0.91) and fat (-16.3, -10.4, 13.6, and 26.3 g/d for I-F:wk 1-12, I-F:wk 1-24, I-T:wk 1-12, and I-T:wk 1-24, respectively; SE = 2.49). Based on energy concentrations in empty body tissue lost or gained in wk 1-12 and 1-24 (14.8, 12.1, 19.9, and 26.4 MJ/kg for I-F:wk 1-12, I-F:wk 1-24, I-T:wk 1-12, and I-T:wk 1-24, respectively; SE = 2.13), the energy concentration in wk 13-24 was 9.4 and 32.9 MJ/kg for I-F and I-T, respectively. In Exp. 2, fasting (5.05, 4.37, 3.16, 4.44, 4.28, and 4.54 MJ/d; SE = 0.34) and fed EE (6.48, 5.97, 4.45, 7.39, 8.44, and 8.47 MJ/d for I-F:Early, I-F:Middle, I-F:Late, I-T:Early, I-T:Middle, and I-T:Late, respectively; SE = 0.58) were influenced by initial body condition x time interactions (P < 0.05). Efficiency of ME utilization (I-F: use of dietary and mobilized tissue energy for maintenance; I-T: use of dietary ME for maintenance and gain) decreased as the experiment advanced (70.5, 60.3, 40.4, 66.7, 64.6, and 60.0% for I-F:Early, I-F:Middle, I-F:Late, I-T:Early, I-T:Middle, and I-T:Late, respectively; SE = 4.85). In conclusion, the energy concentration in tissue mobilized or accreted by yearling meat goats within certain body condition ranges may not necessarily be the same and appears influenced by initial animal characteristics and subsequent feeding conditions.