Tall fescue might be an alternative to timothy in northeastern North America because of its tolerance of recurring drought periods and its good summer regrowth, but is not always considered as an option in dairy rations because of its possible lack of palatability. The objective of this study was to evaluate the effects on the performance of lactating dairy cows of (1) replacing timothy silage by tall fescue silage, offered as sole forage in the diet or in combination with alfalfa silage, and (2) feeding tall fescue as silage (35% dry matter, DM) or haylage (55% DM). Experimental diets with a forage-to-concentrate ratio of 70:30 were (1) 100% timothy silage (TS); (2) 100% tall fescue silage (TFS); (3) 55:45 timothy:alfalfa silages (TS + AS); (4) 55:45 tall fescue:alfalfa silages (TFS + AS); and (5) 100% tall fescue haylage (TFH). Fifteen Holstein cows in mid-lactation (5 fitted with a rumen fistula) were randomly assigned to treatments in a triple 5 × 5 Latin square design with treatment periods of 21 d. Preplanned contrasts were timothy versus tall fescue silages, sole grass species versus grass-alfalfa, interaction between sole grass species and grass-alfalfa, and TFS versus TFH. Grass species did not affect dry matter intake (DMI) or milk yield and fat concentration. Milk protein concentration was not affected by grass species when offered in combination with alfalfa, but it was higher with the TS diet than the TFS diet when offered as sole forages. Adding alfalfa to either tall fescue or timothy silage resulted in greater DMI and milk yield, but lower milk fat concentration, than when the grass silages were the sole forage in the diet. The molar proportion of propionate in the rumen was greater when cows were fed diets with tall fescue silage compared with timothy silage, which resulted in a lower acetate-to-propionate ratio. Milk fat concentrations of fatty acids from microbial origin, namely branched-chain fatty acids, were greater when grass silage, and especially timothy silage, were fed as sole forages rather than with alfalfa silage. Feeding TFH rather than TFS caused a decrease in DMI and tended to lower milk protein concentration, but did not affect milk yield. A more fibrolytic fermentation profile was observed in rumen of cows fed TFH compared with TFS, as indicated by the increase in the molar proportion of acetate and the higher acetate-to-propionate ratio in rumen fluid, and a concomitant increase in branched-chain fatty acid concentration in milk fat. Tall fescue as silage or haylage is a valuable alternative to timothy silage for lactating dairy cows.

在北美东北部地区，高羊茅草可能是替代提摩太草的一种选择，因为它可以忍受反复出现的干旱时期，并且夏季生长良好，但由于可能缺乏适口性，因此并不总是被认为是奶制品的选择。这项研究的目的是评估以下方面对泌乳奶牛性能的影响：（1）用高羊茅饲料代替蒂莫西青贮饲料，作为饲料中的唯一牧草或与苜蓿青贮饲料结合使用；（2）喂养高羊茅作为青贮饲料（35％干物质，DM）或海藻类（55％DM）。饲料与精料比为70:30的实验饮食为（1）100％提莫西青贮（TS）；（2）100％高羊茅饲料（TFS）；（3）55:45提摩太：苜蓿青贮饲料（TS + AS）；（4）55:45高羊茅：苜蓿青贮饲料（TFS + AS）；（5）100％高羊茅草皮（TFH）。泌乳中期的15头荷斯坦奶牛（5头装有瘤胃瘘）被随机分配为采用5×5三重拉丁方格设计的治疗，治疗期为21天。预先计划的对比是提摩太奇与高羊茅青贮饲料，唯一草种与草苜蓿，唯一草种与草苜蓿之间的相互作用以及TFS与TFH。草种不会影响干物质摄入量（DMI）或牛奶产量和脂肪浓度。与苜蓿配合使用时，乳蛋白浓度不受草种的影响，但当单独饲喂TS饲料时，其牛奶蛋白浓度高于TFS饲料。与草料青贮饲料是唯一的饲料相比，在高羊茅或蒂莫西青贮饲料中添加苜蓿可提高DMI和牛奶产量，但降低牛奶脂肪浓度。当饲喂高羊茅青贮饲料时，瘤胃中丙酸酯的摩尔比例要比提莫西青贮饲料的瘤胃中的丙酸酯摩尔比例更大，这会导致乙酸/丙酸酯的比例降低。当草料青贮饲料，尤其是提莫西青贮饲料作为唯一饲料而不是苜蓿青贮饲料时，来自微生物的脂肪酸乳脂浓度，即支链脂肪酸，会更高。饲喂TFH而不是TFS会导致DMI降低，并倾向于降低乳蛋白浓度，但不影响乳汁产量。与TFS相比，饲喂TFH的奶牛的瘤胃中有更强的纤维化发酵特性，这表明瘤胃液中乙酸的摩尔比例增加和乙酸/丙酸比例更高，以及分支链脂肪的伴随增加牛奶脂肪中的酸浓度。