Department of Animal and Range Sciences, New Mexico State University, Las Cruces 88003, USA.
J Anim Sci. 2010 May;88(5):1891-904. doi: 10.2527/jas.2009-2541. Epub 2010 Feb 12.
Balancing growth and reproductive performance in beef cattle managed in desert environments is challenging. Our objectives were to 1) evaluate trends in growth and reproductive traits, and 2) assess associative relationships between growth characteristics and reproductive performance in a Brangus herd managed in a Chihuahuan Desert production system from 1972 to 2006. Data were from bull (n = 597) and heifer calves (n = 585; 1988 to 2006) and cows (n = 525; repeated records of cows, n = 2,611; 1972 to 2006). Variables describing the growth curve of each cow were estimated using a nonlinear logistic function (each cow needed 6 yr of data). Mixed-effect models and logistic regression were used to analyze trends across years in growth and reproductive traits (both continuous and categorical). For continuous traits of calves, a slight cubic response (P < 0.01) described the dynamics of birth weight, 205-d BW, and 365-d BW across years. For categorical traits of females, positive linear trends (P < 0.05) across years were observed in percent pregnant as yearlings, calved at 2 yr of age, and first-calf heifer rebreeding (slopes ranged from 0.007 to 0.014%/yr). Autumn cow BW increased gradually until 1997 (509 kg +/- 8.8) and then decreased gradually by 0.6 kg/yr, whereas pregnancy percentage decreased gradually until 1995 (78.4% +/- 1.0) and then increased slightly by 0.2%/yr. A quadratic effect best described the dynamics of these 2 variables across years (P < 0.01) as well as estimates describing the growth curve of each cow. Specifically, asymptotic BW and age increased (P < 0.05) from 1972 to 1983 and 1990, respectively. Asymptotic age then decreased by 27% from 1983 to 1996 (P < 0.05). The maturing rate index was negatively correlated with age at first calving and calving interval (r = -0.42 and -0.18, P < 0.01), which suggested that early-maturing cows had enhanced fertility in this environment and production system. In summary, minimal changes were observed in measures of growth in bulls and heifers in a Brangus herd managed in the Chihuahuan Desert. Opposing relationships were observed among measures of cow size and fertility; as growth curves shifted toward earlier maturity, measures of reproductive performance suggested that fertility improved.
在沙漠环境中管理的肉牛的生长和繁殖性能之间的平衡具有挑战性。我们的目标是：1）评估生长和繁殖性状的趋势，2）评估在 1972 年至 2006 年期间在奇瓦瓦沙漠生产系统中管理的 Brangus 牛群中生长特征与繁殖性能之间的关联关系。数据来自公牛（n=597）和小母牛（n=585；1988 年至 2006 年）和母牛（n=525；母牛重复记录，n=2611；1972 年至 2006 年）。使用非线性逻辑函数（每头母牛需要 6 年的数据）来估计描述每头母牛生长曲线的变量。混合效应模型和逻辑回归用于分析多年来生长和繁殖性状的趋势（连续和分类）。对于小牛的连续性状，出生体重，205 天 BW 和 365 天 BW 的动态以轻微的立方响应（P<0.01）描述。对于雌性的分类性状，观察到随着年份的线性增长（P<0.05），如一岁时怀孕的百分比，两岁时产犊的百分比和第一胎小母牛的再繁殖（斜率范围为 0.007 至 0.014％/年）。秋季母牛 BW 逐渐增加，直到 1997 年（509 公斤 +/- 8.8），然后每年减少 0.6 公斤，而怀孕百分比逐渐减少，直到 1995 年（78.4% +/- 1.0），然后每年增加 0.2％。二次效应最好地描述了这些 2 个变量在多年来的动态（P<0.01），以及描述每头母牛生长曲线的估计。具体来说，1972 年至 1983 年和 1990 年，渐近 BW 和年龄分别增加（P<0.05）。然后，1983 年至 1996 年，渐近年龄下降了 27％（P<0.05）。成熟率指数与初产年龄和产犊间隔呈负相关（r=-0.42 和-0.18，P<0.01），这表明在这种环境和生产系统中，早熟母牛具有更高的生育能力。总之，在奇瓦瓦沙漠生产系统中管理的 Brangus 牛群中，公牛和小母牛的生长指标几乎没有变化。母牛大小和生育能力之间存在相反的关系；随着生长曲线向更早的成熟度转移，繁殖性能的指标表明生育能力得到了提高。
