Soto-Navarro S A, Lopez R, Sankey C, Capitan B M, Holland B P, Balstad L A, Krehbiel C R
Department of Animal and Range Sciences, New Mexico State University, Las Cruces 88003.
J Anim Sci. 2014 Apr;92(4):1621-9. doi: 10.2527/jas.2013-6740. Epub 2014 Mar 18.
The objective was to determine the effect of forage quality on apparent total tract digestibility and ruminal fermentation in cattle versus sheep. Five yearling English crossbred (Hereford × Angus) steers (440.4 ± 35.6 kg of initial BW) and 5 yearling whiteface (Rambouillet × Columbia × Debouillet) wethers (44.4 ± 4.6 kg of initial BW), each fitted with a ruminal cannula, were randomly assigned to 1 of 3 forage sources within ruminant specie, and the study was conducted over 3 periods. For forage source, both animal and period served as the blocking factor with all forage sources represented once within each animal and all forage sources represented at least once within each period. The treatment structure was arranged in a 2 × 3 factorial with ruminant species (2) and forage source (3) as the factors. Forage sources were 1) alfalfa hay (Medicago sativa; 17.5% CP and 34.1% NDF, DM basis), 2) warm-season grass hay mix (Bothriochloa ischaemum and Cynodon dactylon; 7.3% CP and 74.7% NDF, DM basis), and 3) lovegrass hay (Eragrostis curvula; 2.5% CP and 81.9% NDF, DM basis). As a percent of BW, steers and wethers consumed similar (P ≤ 0.06) amounts of forage, and intake was more influenced by forage quality (P < 0.001) than ruminant species (P = 0.35). When expressed per unit of metabolic BW, cattle consumed more (P < 0.001) DM, NDF, and N than sheep. Apparent total tract digestibility was similar among steers and wethers when alfalfa or grass hay was fed, but decreased to a greater extent in wethers when low-quality lovegrass hay was fed (ruminant species × diet interaction, P ≤ 0.01). Rate (%/h) of ruminal NDF disappearance was greater (P = 0.02) for alfalfa and grass hay than lovegrass, but was not influenced (P = 0.12) by ruminant species. In addition, ruminal DM fill was influenced more (P < 0.01) by forage than by ruminant species (P = 0.07). Steers and wethers had greater (P < 0.01) DM fill from grass hay and lovegrass hay than alfalfa before and 5 h after feeding. Ruminal VFA were generally not influenced (P ≥ 0.06) by ruminant specie. Results suggest that apparent total tract digestibilities are more similar among ruminant species when moderate- to high-quality forages are evaluated. However, sheep are not an adequate model for cattle when low-quality forages are compared because cattle digest low-quality forages to a greater extent than sheep. Expressing digestibility as digestible intake per unit of BW allows for a wider range of forage qualities to be compared when substituting sheep for cattle.
目的是确定饲料质量对牛和羊的表观全消化道消化率及瘤胃发酵的影响。选用5头一岁的英国杂交（赫里福德×安格斯）公牛（初始体重440.4±35.6千克）和5头一岁的白面（兰布耶×哥伦比亚×德布伊耶）阉羊（初始体重44.4±4.6千克），每头都安装有瘤胃瘘管，在反刍动物种类内随机分配到3种饲料来源之一，研究分3个阶段进行。对于饲料来源，动物和阶段均作为区组因素，每种动物内所有饲料来源各出现一次，每个阶段内所有饲料来源至少出现一次。处理结构按2×3析因设计，以反刍动物种类（2）和饲料来源（3）作为因素。饲料来源分别为：1）苜蓿干草（紫花苜蓿；粗蛋白含量17.5%，中性洗涤纤维含量34.1%，干物质基础），2）暖季禾本科混合干草（白羊草和狗牙根；粗蛋白含量7.3%，中性洗涤纤维含量74.7%，干物质基础），3）画眉草干草（弯叶画眉草；粗蛋白含量2.5%，中性洗涤纤维含量81.9%，干物质基础）。以体重百分比计，公牛和阉羊消耗的饲料量相似（P≤0.06），且采食量受饲料质量的影响更大（P<0.001），而非反刍动物种类（P=0.35）。以每单位代谢体重表示时，公牛消耗的干物质、中性洗涤纤维和氮比阉羊更多（P<0.001）。饲喂苜蓿或禾本科干草时，公牛和阉羊的表观全消化道消化率相似，但饲喂低质量的画眉草干草时，阉羊消化率下降幅度更大（反刍动物种类×日粮互作，P≤0.01）。苜蓿和禾本科干草的瘤胃中性洗涤纤维消失率（%/小时）高于画眉草（P=0.02），但不受反刍动物种类影响（P=0.12）。此外，瘤胃干物质充盈度受饲料的影响大于反刍动物种类（P<0.01对P=0.07）。饲喂前及饲喂后5小时，公牛和阉羊采食禾本科干草和画眉草干草后的干物质充盈度高于苜蓿（P<0.01）。瘤胃挥发性脂肪酸一般不受反刍动物种类影响（P≥0.06）o结果表明，评估中高质量饲料时，反刍动物种类间的表观全消化道消化率更相似。然而，比较低质量饲料时，羊不能作为牛的合适模型，因为牛对低质量饲料的消化程度高于羊。以每单位体重的可消化采食量表示消化率时，用羊替代牛可比较更广泛的饲料质量范围。
