Growth and carcass traits of Boer × Alpine wethers slaughtered at the ages of 31 and 50 weeks
J. Luo, T. Sahlu, and A. L. GoetschJournal of Animal and Feed Sciences 9:309-316. 2000.
The Alpine goat has high milk production but low rates of carcass fat and protein deposition compared with traditional meat goat breeds. Thus, crossbreeding Alpines with a meat goat breed is a means of increasing profit potential from sale of kids for meat production. Boer goats are more muscular and larger in mature size than other breeds of goats; thus, crossing the Alpine goat with the Boer could produce a genotype with high growth rate and carcass characteristics suitable for goat meat market specifications. Changes in body weight gain, feed efficiency, and carcass characteristics with advancing age are well understood for cattle and sheep. Briefly, efficiency of feed utilization and body weight gain decrease with advancing time as adipose tissue accretion increases and lean tissue deposition declines, although degrees of change vary with factors such as particular stages of maturity, diet composition, and previous nutritional plane. Concomitantly, whole body fat content increases with age, again with magnitudes of change for different depots or sites depending on aforementioned conditions. For goats, presently high carcass fat levels are not desired by U.S. consumers. Thus, there is need to evaluate differences in efficiency of production and carcass characteristics between meat goats of different ages, in order to determine optimal ages and times for slaughter. In this regard, 14 Boer × Alpine wethers were used to determine effects of feeding from 15 to 31 weeks (Phase 1) and from 38 to 50 weeks (Phase 2) on feed intake, body weight gain, feed efficiency, plasma constituents, internal organ mass, and carcass traits. All wethers consumed diets free-choice with 20 and 16% crude protein and 33 and 40% neutral detergent fiber diet in Phase 1 and 2, respectively. Body weight after Phase 1 and 2 was 42 and 57 kg, respectively; body weight gain was greater in Phase 1 than in Phase 2 (228 vs 118 g/day); and the ratio of BW gain to dry matter intake differed between phases (0.19 in Phase 1 vs 0.10 in Phase 2). Cold carcass weight (20.4 vs 29.6 kg), dressing percentage (50.1 vs 56.5%), and percentage of carcass fat (16.4 vs 20.2%) were greater after Phase 2 than Phase 1, and leg cut percentage (30.5 vs 28.3%), carcass bone percentage (23.7 vs 20.6%), and backfat thickness (0.44 vs 0.30 cm) were greater after Phase 1. However, carcass lean percentage (58.3 and 57.1%) and the percentage of noncarcass fat (6.39 and 7.07% for Phase 1 and 2, respectively) were similar between phases. In conclusion, Boer × Alpine male castrates had appreciably greater BW gain and FCR in Phase 1 (14 to 31 wk of age) than in Phase 2 (38 to 50 wk of age). Most important carcass characteristics favourably affected by the lengthy feeding period were carcass weight and dressing percentage. In general, age did not have appreciable effects on other carcass characteristics, although the carcass fat percentage was 3.8 percentage units greater after Phase 2 than after Phase 1. Overall, it would appear that considerably more desirable marketing opportunities after Phase 2 than after Phase 1 would be required to justify the high feed costs of Phase 2 for Boer × Alpine wethers.
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