Brown M A, Brown A H
USDA, ARS, Grazinglands Research Laboratory, El Reno, OK 73036, USA.
J Anim Sci. 2002 Oct;80(10):2522-7.
Interactions of the regression of preweaning ADG on dam milk yield and quality with breed group and forage environment were evaluated in a two-phase study. Phase I consisted of milk yield and quality and calf gain records from 1989 to 1991 for purebred Angus (n = 64) and Brahman (n = 62) cows mated to sires of both breeds. Phase II consisted of milk yield and quality and calf gain records from 1991 to 1997 for Angus (n = 94), Brahman (n = 85), Angus x Brahman (n = 86) and Brahman x Angus (n = 93) mated to Polled Hereford sires. In Phase I, forage environments included common bermudagrass and endophyte-infected tall fescue. In Phase II, forage environments included common bermudagrass and endophyte-infected tall fescue (1991 to 1995) and a rotational system of both forages (1995 to 1997) in which each forage was grazed during its appropriate growing season, usually June through October for bermudagrass and November through May for tall fescue. Milk yield was estimated monthly six times during lactation from spring through fall and converted to a 24-h basis. Milk fat, milk protein, and somatic cell count were analyzed by a commercial laboratory. In Phase I, the relation of preweaning ADG to milk yield, milk fat yield, and protein yield was greater (P < 0.05) in Brahman cows on bermudagrass than Angus on bermudagrass. The regression of preweaning ADG on milk yield in Phase I was greater (P < 0.05) for cows on tall fescue than cows which grazed bermudagrass. In Phase II, the relation of preweaning ADG to milk yield, milk fat yield, and milk protein yield was greater or tended to be greater (P < 0.01, P < 0.11, P < 0.01, respectively) in purebred cows compared to reciprocal-cross cows. The regression of preweaning ADG on milk yield and milk protein yield was greater (P < 0.05) on tall fescue than bermudagrass in Phase II. These results suggest that the influence of milk yield and quality on calf growth may differ among breed types and production system, and the efficacy of genetic improvements in milk traits may depend on the breed type and forage environment.
在一项两阶段研究中，评估了断奶前平均日增重（ADG）对母牛产奶量和质量的回归与品种组及草料环境之间的相互作用。第一阶段包括1989年至1991年纯种安格斯牛（n = 64）和婆罗门牛（n = 62）与两个品种公牛交配后的产奶量、质量及犊牛增重记录。第二阶段包括1991年至1997年安格斯牛（n = 94）、婆罗门牛（n = 85）、安格斯×婆罗门杂交牛（n = 86）和婆罗门×安格斯杂交牛（n = 93）与无角海福特公牛交配后的产奶量、质量及犊牛增重记录。在第一阶段，草料环境包括普通百慕大草和内生菌感染的高羊茅。在第二阶段，草料环境包括普通百慕大草和内生菌感染的高羊茅（1991年至1995年）以及两种草料的轮作系统（1995年至1997年），其中每种草料在其适宜的生长季节放牧，通常百慕大草从6月到10月，高羊茅从11月到次年5月。在春季到秋季的泌乳期内每月估计一次产奶量，共六次，并换算为24小时的产量。乳脂、乳蛋白和体细胞计数由一家商业实验室进行分析。在第一阶段，婆罗门母牛在百慕大草上的断奶前ADG与产奶量、乳脂产量和蛋白产量之间的关系比在百慕大草上的安格斯母牛更强（P < 0.05）。第一阶段，在高羊茅上的母牛断奶前ADG对产奶量的回归比放牧百慕大草的母牛更强（P < 0.05）。在第二阶段，与杂交母牛相比，纯种母牛断奶前ADG与产奶量、乳脂产量和乳蛋白产量之间的关系更强或趋于更强（分别为P < 0.01、P < 0.11、P < 0.01）。在第二阶段，高羊茅上断奶前ADG对产奶量和乳蛋白产量的回归比百慕大草更强（P < 0.05）。这些结果表明，产奶量和质量对犊牛生长的影响可能因品种类型和生产系统而异，并且乳用性状遗传改良的效果可能取决于品种类型和草料环境。
