Oklahoma Agricultural Experiment Station; Stillwater, Oklahoma 74078, USA.
J Anim Sci. 2013 Sep;91(9):4322-35. doi: 10.2527/jas.2012-5440. Epub 2013 Jul 12.
Two experiments were conducted to examine the effect of growth rate to similar age or BW on fat deposition in stocker cattle grazing dormant native range (DNR) or winter wheat pasture (WP). In each experiment, fall-weaned Angus steers were randomly allotted to 1 of 4 stocker production programs: 1) control, 1.02 kg/d of a 40% CP cottonseed meal-based supplement during grazing of DNR (CON); 2) corn/soybean meal-based supplement fed at 1% of BW during grazing of DNR (CORN); 3) grazing WP at a high stocking rate to achieve a low rate of BW gain (LGWP); and 4) grazing WP at a low stocking rate to achieve a high rate of BW gain (HGWP). In Exp. 1, a subset of steers (3 steers per treatment) was harvested after winter grazing (138 d) at similar age. The remaining WP steers were transitioned into the finishing phase, whereas DNR steers were allowed to graze the same native range pastures for another 115 d without supplementation before entering the feedyard. In Exp. 2, steers grazed their respective pastures until each treatment reached an estimated HCW of 200 kg (262, 180, 142, and 74 d, respectively, for the CON, CORN, LGWP, and HGWP treatments), at which time a subset of steers (4 steers per treatment) were selected for intermediate harvest before finishing. In both experiments, the remaining steers were fed a finishing diet to a common 12th-rib fat thickness of 1.27 cm. In Exp. 1, winter grazing ADG was 0.19, 0.52, 0.68, and 1.37 ± 0.03 kg/d; and in Exp. 2, winter/summer grazing ADG was 0.46, 0.61, 0.83, and 1.29 ± 0.02 kg/d, respectively for CON, CORN, LGWP, and HGWP treatments. At intermediate harvest in Exp. 1, HGWP steers had greater (P < 0.01) 12th-rib fat thickness and marbling scores, compared with the other treatments. However, in Exp. 2, LGWP steers had greater (P < 0.01) marbling scores compared with HGWP steers, which were greater than DNR steers. At final harvest in Exp. 1, LGWP steers had greater (P < 0.01) 12th-rib fat thickness and smaller LM area, compared with the other treatments; however, there were no differences (P = 0.99) in final marbling scores. In Exp. 2, CON steers had lower (P < 0.05) 12th-rib fat thickness and tended (P = 0.10) to have greater marbling scores, compared with the other treatments. These data suggest that changes in the partitioning of fat among depots during the stocker phase may not be reflected after finishing when steers are fed to a common 12th-rib fat thickness.
进行了两项实验，以检验生长速度与相似年龄或 BW 对育肥牛放牧休眠原生植被（DNR）或冬季小麦牧场（WP）时脂肪沉积的影响。在每个实验中，秋季断奶的安格斯阉牛随机分配到 4 个育肥生产方案中的 1 个：1）对照，在放牧 DNR 时补充 40% CP 棉籽粉基补充料 1.02kg/d（CON）；2）在放牧 DNR 时以 BW 的 1%补充玉米/豆粕基补充料（CORN）；3）在高放牧率下放牧 WP 以实现低 BW 增长率（LGWP）；和 4）在低放牧率下放牧 WP 以实现高 BW 增长率（HGWP）。在实验 1 中，一组阉牛（每个处理 3 头）在冬季放牧（138 天）后以相似的年龄进行收获。其余 WP 阉牛被转入育肥阶段，而 DNR 阉牛则在进入饲料场前被允许在同一原生牧场放牧 115 天而不补充饲料。在实验 2 中，阉牛在各自的牧场上放牧，直到每个处理达到估计的 HCW 为 200kg（CON、CORN、LGWP 和 HGWP 处理分别为 262、180、142 和 74d），此时每个处理选择 4 头阉牛（每个处理 4 头）进行中间收获，然后进行育肥。在这两个实验中，其余的阉牛都被喂食育肥日粮，直到第十二肋脂肪厚度达到 1.27cm。在实验 1 中，冬季放牧 ADG 分别为 0.19、0.52、0.68 和 1.37±0.03kg/d；在实验 2 中，冬季/夏季放牧 ADG 分别为 0.46、0.61、0.83 和 1.29±0.02kg/d，分别为 CON、CORN、LGWP 和 HGWP 处理。在实验 1 的中间收获时，HGWP 阉牛的第十二肋脂肪厚度和大理石纹评分均显著高于其他处理（P<0.01）。然而，在实验 2 中，LGWP 阉牛的大理石纹评分显著高于 HGWP 阉牛，而 HGWP 阉牛的大理石纹评分又显著高于 DNR 阉牛。在实验 1 的最终收获时，LGWP 阉牛的第十二肋脂肪厚度较大（P<0.01），LM 面积较小，与其他处理相比；然而，最终大理石纹评分没有差异（P=0.99）。在实验 2 中，CON 阉牛的第十二肋脂肪厚度较低（P<0.05），大理石纹评分较高（P=0.10），与其他处理相比。这些数据表明，育肥期脂肪在不同部位之间的分配变化在育肥结束时当阉牛被喂食到相同的第十二肋脂肪厚度时可能不会反映出来。
