Magaña J G, Segura-Correa J C
Facultad de Medicina Veterinaria y Zootecnia, UADY, Mérida, Yucatán, México.
J Anim Breed Genet. 2006 Feb;123(1):37-43. doi: 10.1111/j.1439-0388.2006.00556.x.
The objective of this study was to evaluate the body weights up to 18 months of age of 12 breed groups of Zebu (Z), Brown Swiss (BS) and Charolais heifers (CH), and their crosses under tropical conditions. A total of 1434 data on weaning weights adjusted to 240 days (WW8), average daily gain to 240 days (ADG8) and 1025 body weights adjusted to 550 days (BW18) and average postweaning daily gain (ADG18) of heifers born from 1981 to 1995 were used. Cows and calves remained together from birth to weaning and grazed on Guinea grass (Panicum maximum). Years of birth were grouped in three periods, because of the small numbers of observations per year (1981-85, 1986-90 and 1991-95). Similarly, months of birth were grouped in three seasons: dry (February to May), rainy (June to September) and windy and rainy (October to January). Ages of dams were classified in six groups (<or=3, 4, 5, 6, 7 and >or=8 years). Breed groups were animals with 12.5%, 25.0%, 50.0%, 62.5%, 75.0% and 100% BS genes and 25.0%, 50.0%, 75.0% and 100% CH genes and also Z and undefined crossbred animals. Data were analysed using a fixed model that included effects of period, and season of birth, age of dam and breed group of heifer. Analyses of variance showed significant (p < 0.05) effects of period, season and breed group for all traits. However, parity was significant (p < 0.05) only for WW8 and ADG8. Interactions among main factors were not significant (p > 0.05). Z heifers gained the least weight to weaning but were similar to BS at 18 months of age. CH were heavier at 18 months of age than BS heifers, but not at weaning. Body weights at 18 months of age of 1/8 and 1/4 BS crossbred heifers were similar (p > 0.05) and lower than F1 (BS x Z) (p < 0.05); however, the later and higher grades of BS had the highest body weights at 18 months of age and were similar to CH and 1/4 CH x 3/4 Z heifers. Undefined crossbred heifers had better performance than the Z breed group. Environmental factors were important sources of variation for pre- and postweaning traits. Under the conditions of this study, crossbred heifers generally performed better than Z heifers up to 18 months of age.
本研究的目的是评估瘤牛（Z）、瑞士褐牛（BS）和夏洛来母牛（CH）的12个品种组及其杂交后代在热带条件下至18月龄的体重。使用了1981年至1995年出生的小母牛的总共1434个数据，这些数据包括调整至240天的断奶体重（WW8）、至240天的平均日增重（ADG8）、调整至550天的1025个体重（BW18）以及断奶后平均日增重（ADG18）。母牛和小牛从出生到断奶一直在一起，并在几内亚草（大黍）上放牧。由于每年的观测数量较少（1981 - 85年、1986 - 90年和1991 - 95年），出生年份被分为三个时期。同样，出生月份被分为三个季节：旱季（2月至5月）、雨季（6月至9月）和风雨季（10月至1月）。母牛的年龄分为六组（≤3、4、5、6、7和≥8岁）。品种组包括具有12.5%、25.0%、50.0%、62.5%、75.0%和100% BS基因以及25.0%、50.0%、75.0%和100% CH基因的动物，还有瘤牛和未定义的杂交动物。数据使用固定模型进行分析，该模型包括时期、出生季节、母牛年龄和小母牛品种组的影响。方差分析表明，所有性状的时期、季节和品种组效应均显著（p < 0.05）。然而，胎次仅对WW8和ADG8显著（p < 0.05）。主要因素之间的相互作用不显著（p > 0.05）。瘤牛小母牛断奶时增重最少，但在18月龄时与瑞士褐牛相似。夏洛来母牛在18月龄时比瑞士褐牛重，但断奶时并非如此。1/8和1/4瑞士褐牛杂交小母牛在18月龄时的体重相似（p > 0.05）且低于F1（瑞士褐牛×瘤牛）（p < 0.05）；然而，更高等级的瑞士褐牛在18月龄时体重最高，且与夏洛来母牛和1/4夏洛来×3/4瘤牛小母牛相似。未定义的杂交小母牛比瘤牛品种组表现更好。环境因素是断奶前和断奶后性状变异的重要来源。在本研究条件下，杂交小母牛在18月龄前通常比瘤牛小母牛表现更好。
