Effects of diet quality and age of meat goat wethers on early subsequent growth while grazing wheat forage

Thirty six meat goat wethers (3/4 Spanish and 1/4 Boer), born in the previous Spring (initial age and BW of 8.5 months and 17 ± 0.6 kg) or Fall (initial age of 2.5 months and 13 ± 0.8 kg), were used to determine effects of ad libitum consumption of different quality diets and age on early subsequent growth while grazing wheat forage. The experiment was 14 weeks long, with 9 weeks in the winter consuming prairie hay (5% CP and 71% NDF) supplemented with 0.125% BW of soybean meal (PH), alfalfa pellets (AP) or a 70% concentrate diet (CD), and 5 weeks in the spring grazing wheat forage. ADG in Period 1 (28, 54 and 81 g per day; S.E. = 14.0) and Period 2 (123, 137 and 100 g per day for PH, AP and CD, respectively; S.E. = 13.8) was similar among dietary treatments and greater for Spring vs. Fall wethers (Period 1: 72 vs. 37 g per day,P < 0.05; Period 2: 131 vs. 108 g per day, P < 0.09). There was not a discernible pattern of change in ADG as week of grazing wheat forage advanced (week 1: 65 and 22 g per day; week 2: 236 and 188 g per day; week 3: 65 and 105 g per day; week 4: 49 and 23 g per day; week 5: 249 and 215 g per day for Spring and Fall, respectively). Body composition (estimated from shrunk BW and urea space) on days 42 and 98 and composition of gain were similar among dietary treatments. Differences between ages (P < 0.05) in protein mass on day 42 (2.92 and 2.65 kg for Spring and Fall, respectively) and 98 (3.72 and 3.36 kg for Spring and Fall, respectively) were similar in magnitude, although that in fat mass on day 98 (4.60 and 3.31 kg) was considerably greater than on day 42 (2.39 and 1.96 kg for Spring and Fall, respectively). In accordance, protein accretion from day 42 to 98 was similar between ages (14.3 and 12.6 g per day for Spring and Fall, respectively; S.E. = 0.86), whereas rate of fat accretion was greater (P < 0.05) for Spring vs. Fall wethers (39.6 vs. 24.1 g per day). In conclusion, the nature of the diet consumed ad libitum did not impact subsequent growth by 3/4 Spanish wethers, regardless of age, when grazing wheat forage. © 2003 Elsevier B.V. All rights reserved.