Retired - U.S. Department of Agriculture, Agricultural Research Service, Grazinglands Research Laboratory, El Reno, OK.
U.S. Department of Agriculture, Agricultural Research Service, U.S. Meat Animal Research Center, Clay Center, NE.
J Anim Sci. 2018 Jun 4;96(6):2438-2452. doi: 10.1093/jas/sky138.
Earlier work has shown that young tropically adapted cattle do not gain weight as rapidly as temperately adapted cattle during the winter in Oklahoma. The objective for this study was to determine whether efficiency of gains was also affected in tropically adapted cattle and whether efficiency was consistent over different seasons. Over 3 yr, 240 straightbred and crossbred steers (F1 and 3-way crosses) of Angus, Brahman, or Romosinuano breeding, born in Brooksville, FL, were transported to El Reno, OK in October and fed in 2 phases to determine performance, individual intake, and efficiency. Phase 1 (WIN) began in November after a 28-d recovery from shipping stress and phase 2 (SS) began in March, 28 d following completion of WIN each year. The diet for WIN was a grower diet (14% CP, 1.10 Mcal NEg/kg) and that for the SS was a feedlot diet (12.8% CP; 1.33 Mcal NEg/kg). After a 14-d adjustment to diet and facilities, intake trials were conducted over a period of 56 to 162 d for determination of intake and gain for efficiency. Body weights were recorded at approximately 14-d intervals, and initial BW, median BW, and ADG were determined from individual animal regressions of BW on days on feed. Individual daily DMI was then regressed by phase on median BW and ADG, and residuals of regression were recorded as residual feed intake (RFI). Similarly, daily gain was regressed by phase on median BW and DMI, and errors of regression were recorded as residual gain (RADG). Gain to feed (G:F) was also calculated. The statistical model to evaluate ADG, DMI, and efficiency included fixed effects of dam age (3 to 4, 5, 6 to 10, and >10 yr), harvest group (3 per year), age on test, and a nested term DT (ST × XB), where DT is the proportion tropical breeding of dam (0, 0.5, or 1), ST is the proportion tropical breeding of sire (1 or 0), and XB whether the calf was straightbred or crossbred. Year of record, sire (ST × XB), and pen were random effects. Preweaning ADG and BW increased (P < 0.05) with level of genetic tropical influence, but during the WIN, ADG and efficiency estimated by G:F and RADG declined (P < 0.05). Tropical influence had little effect on RFI during the WIN, or on most traits during SS. In general, during SS, crossbred steers gained faster and were more efficient by G:F and RADG (P < 0.05) than straightbred steers. Simple correlations, both Pearson and Spearman, between RFI in WIN and RFI in SS were 0.51 (P < 0.001), whereas that for RADG was 0.17 (P < 0.01).
早期的研究表明，在俄克拉荷马州的冬季，热带适应的小牛的体重增加速度不如温带适应的小牛快。本研究的目的是确定热带适应的牛的增重效率是否也受到影响，以及效率是否在不同季节保持一致。在 3 年的时间里，240 头安格斯、婆罗门或罗莫西努阿诺纯种和杂交牛（F1 和 3 向杂交），出生于佛罗里达州的布鲁克斯维尔，10 月被运到俄克拉荷马州的埃勒诺，并分 2 个阶段饲养，以确定性能、个体摄入量和效率。第 1 阶段（WIN）于 11 月开始，在运输应激后进行了 28 天的恢复，第 2 阶段（SS）于每年 WIN 结束后的第 28 天开始。WIN 的饮食是生长者饮食（14%CP，1.10 Mcal NEg/kg），SS 的饮食是育肥饮食（12.8%CP；1.33 Mcal NEg/kg）。在适应饮食和设施 14 天后，进行了为期 56 至 162 天的摄入量试验，以确定效率的摄入量和增益。体重每隔约 14 天记录一次，初始 BW、中位数 BW 和 ADG 是从 BW 对饲料天数的个体动物回归中确定的。然后，通过阶段将个体每日 DMI 回归到中位数 BW 和 ADG 上，并记录回归的残差作为残留饲料摄入量（RFI）。同样，通过阶段将每日增益回归到中位数 BW 和 DMI 上，并记录回归的误差作为剩余增益（RADG）。还计算了增重与饲料的比值（G:F）。评估 ADG、DMI 和效率的统计模型包括 DAM 年龄（3 至 4、5、6 至 10 和>10 岁）、收获组（每年 3 个）、试验时的年龄和嵌套项 DT（ST × XB）的固定效应，其中 DT 是 DAM 的热带育种比例（0、0.5 或 1），ST 是 sire 的热带育种比例（1 或 0），XB 是小牛是纯种还是杂交。记录年份、 sire（ST × XB）和围栏是随机效应。断奶前 ADG 和 BW 随着遗传热带影响水平的增加而增加（P < 0.05），但在 WIN 期间，通过 G:F 和 RADG 估计的 ADG 和效率下降（P < 0.05）。在 WIN 期间，热带影响对 RFI 的影响很小，或者对 SS 期间的大多数性状影响很小。一般来说，在 SS 期间，杂交牛的 ADG 增加更快，通过 G:F 和 RADG（P < 0.05）比纯种牛更有效。WIN 中的 RFI 与 SS 中的 RFI 之间的 Pearson 和 Spearman 简单相关系数分别为 0.51（P < 0.001），而 RADG 的相关系数为 0.17（P < 0.01）。
