Hersom M J, Horn G W, Krehbiel C R, Phillips W A
Department of Animal Science, Oklahoma State University, Stillwater 74078, USA.
J Anim Sci. 2004 Jan;82(1):262-72. doi: 10.2527/2004.821262x.
Two experiments were conducted to examine the effect of previous BW gain during winter grazing on subsequent growth, carcass characteristics, and change in body composition during the feedlot finishing phase. In each experiment, 48 fall-weaned Angus x Angus-Hereford steer calves were assigned randomly to one of three treatments: 1) high rate of BW gain grazing winter wheat (HGW), 2) low rate of BW gain grazing winter wheat (LGW), or 3) grazing dormant tallgrass native range (NR) supplemented with 0.91 kg/d of cottonseed meal. Winter grazing ADG (kg/d) for HGW, LGW, and NR steers were, respectively, 1.31, 0.54, 0.16 (Exp. 1) and 1.10, 0.68, 0.15 (Exp. 2). At the end of winter grazing, four steers were selected randomly from each treatment to measure initial carcass characteristics and chemical composition of carcass, offal, and empty body. All remaining steers were fed a high-concentrate diet to a common backfat end point. Six steers were selected randomly from each treatment for final chemical composition, and carcass characteristics were measured on all steers. Initial fat mass and proportion in carcass, offal, and empty body were greatest (P < 0.001) for HGW, intermediate for LGW, and least for NR steers in both experiments. Live BW ADG and gain efficiency during the finishing phase did not differ (P = 0.24) among treatments, but DMI (% of mean BW) for NR and LGW was greater (P < 0.003) than for HGW steers. Final empty-body composition did not differ (P = 0.25) among treatments in Exp. 1. In Exp. 2, final carcass and empty-body fat proportion (g/kg) was greater (P < 0.03) for LGW and NR than for HGW steers. Accretion of carcass fat-free organic matter was greater (P < 0.004) for LGW than for HGW and NR steers in Exp. 1, but did not differ (P = 0.22) among treatments in Exp. 2. Fat accretion in carcass, offal, and empty body did not differ (P = 0.19) among treatments in Exp. 1, but was greater (P < 0.05) for LGW and NR than for HGW steers in Exp. 2. Heat production by NR steers during finishing was greater (P < 0.02) than by HGW steers in Exp. 1 and 2. Differences in ADG during winter grazing and initial body fat content did not affect rate of live BW gain or gain efficiency during finishing. Feeding steers to a common backfat thickness end point mitigated initial differences in carcass and empty-body fat content. However, maintenance energy requirements during finishing were increased for nutritionally restricted steers that were wintered on dormant native range.
进行了两项试验，以研究冬季放牧期间先前的体重增加对育肥期后续生长、胴体特性及体成分变化的影响。在每项试验中，48头秋季断奶的安格斯×安格斯-赫里福德阉牛犊被随机分配到三种处理之一：1）冬季小麦放牧期体重增加率高（HGW）；2）冬季小麦放牧期体重增加率低（LGW）；3）放牧休眠的高草天然牧场（NR）并每日补饲0.91千克棉籽粕。HGW、LGW和NR组阉牛冬季放牧期的平均日增重（ADG，千克/天）分别为1.31、0.54、0.16（试验1）和1.10、0.68、0.15（试验2）。冬季放牧结束时，从每个处理中随机挑选4头阉牛，测量其初始胴体特性以及胴体、内脏和空体的化学成分。其余所有阉牛均饲喂高能量日粮至相同的背膘厚度终点。从每个处理中随机挑选6头阉牛测定最终化学成分，并对所有阉牛测量胴体特性。在两项试验中，HGW组阉牛胴体、内脏和空体的初始脂肪量及比例均最高（P<0.001），LGW组居中，NR组最低。育肥期的活体重ADG和增重效率在各处理间无差异（P=0.24），但NR组和LGW组的干物质采食量（占平均体重的百分比）高于HGW组阉牛（P<0.003）。试验1中各处理间最终空体成分无差异（P=0.25）。试验2中，LGW组和NR组阉牛的最终胴体和空体脂肪比例（克/千克）高于HGW组（P<0.03）。试验1中，LGW组阉牛胴体无脂有机物质的沉积量高于HGW组和NR组（P<0.004），但试验2中各处理间无差异（P=0.22）。试验1中各处理间胴体、内脏和空体的脂肪沉积无差异（P=0.19），但试验2中LGW组和NR组高于HGW组（P<0.05）。试验1和试验2中，NR组阉牛育肥期的产热量高于HGW组（P<0.02）。冬季放牧期的ADG差异及初始体脂含量不影响育肥期的活体重增加率或增重效率。将阉牛饲喂至相同的背膘厚度终点可减轻胴体和空体脂肪含量的初始差异。然而，在休眠天然牧场越冬的营养受限阉牛育肥期的维持能量需求增加。
