Department of Animal Science, University of Nebraska, Lincoln 68583-0908, USA.
J Anim Sci. 2011 Nov;89(11):3452-9. doi: 10.2527/jas.2011-3961. Epub 2011 May 27.
Growth, feed intake, and temperament indicator data, collected over 5 yr on a total of 1,141 to 1,183 mixed-breed steers, were used to estimate genetic and phenotypic parameters. All steers had a portion of Hereford, Angus, or both as well as varying percentages of Simmental, Charolais, Limousin, Gelbvieh, Red Angus, and MARC III composite. Because the steers were slaughtered on various dates each year and the animals thus varied in days on feed, BW and feed data were adjusted to a 140-d feeding period basis. Adjustment of measures of feed efficiency [G:F or residual feed intake (RFI), intake adjusted for metabolic body size, and BW gain] for body fatness recorded at slaughter had little effect on the results of analyses. Average daily gain was less heritable (0.26) than was midtest BW (MBW; 0.35). Measures of feed intake had greater estimates of heritability, with 140-d DMI at 0.40 and RFI at 0.52; the heritability estimate for G:F was 0.27. Flight speed (FS), as an indicator of temperament, had an estimated heritability of 0.34 and a repeatability of 0.63. As expected, a strong genetic (0.86) correlation was estimated between ADG and MBW; genetic correlations were less strong between DMI and ADG or MBW (0.56 and 0.71). Residual feed intake and DMI had a genetic correlation of 0.66. Indexes for phenotypic RFI and genotypically restricted RFI (no correlation with BW gain) were compared with simple economic indexes incorporating feed intake and growth to elucidate expected selection responses under different criteria. In general, few breed differences were detected across the various measurements. Heterosis contributed to greater DMI, RFI, and MBW, but it did not significantly affect ADG, G:F, or FS. Balancing output (growth) with input costs (feed) is needed in practicing selection, and FS would not be recommended as an indicator trait for selection to change feed efficiency. An index including BW gain and RFI produced the best economic outcome.
在总共 1141 到 1183 头杂种阉牛身上收集了 5 年的生长、采食量和气质指标数据，用于估计遗传和表型参数。所有的阉牛都有一部分荷斯坦牛、安格斯牛或两者的血统，以及不同比例的西门塔尔牛、夏洛来牛、利木赞牛、金德雷牛、红安格斯牛和 MARC III 杂交牛。由于阉牛每年在不同的日期被屠宰，因此动物在饲养期间的天数不同，体重和饲料数据被调整为 140 天的饲养期基础。调整屠宰时记录的体脂率对饲料效率[G:F 或剩余饲料摄入量 (RFI)、代谢体尺调整后的采食量和体重增加]措施的分析结果影响不大。平均日增重的遗传力（0.26）低于中测体重（MBW；0.35）。采食量的衡量标准具有更高的遗传力估计值，其中 140 天的 DMI 为 0.40，RFI 为 0.52；G:F 的遗传力估计值为 0.27。飞行速度（FS）作为气质指标，遗传力估计值为 0.34，重复性为 0.63。正如预期的那样，ADG 和 MBW 之间估计出了很强的遗传（0.86）相关性；DMI 和 ADG 或 MBW 之间的遗传相关性较弱（0.56 和 0.71）。RFI 和 DMI 具有 0.66 的遗传相关性。表型 RFI 和基因型限制 RFI（与体重增加无相关性）的指数与包含采食量和生长的简单经济指数进行了比较，以阐明在不同标准下预期的选择反应。一般来说，在各种测量中发现的品种差异很小。杂种优势导致 DMI、RFI 和 MBW 增加，但对 ADG、G:F 或 FS 没有显著影响。在进行选择时，需要平衡产出（生长）和投入成本（饲料），并且不建议将 FS 作为改变饲料效率的选择指标。包含 BW 增益和 RFI 的指数产生了最佳的经济结果。
