Department of Animal Sciences, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691, USA.
J Dairy Sci. 2009 Dec;92(12):6144-55. doi: 10.3168/jds.2009-2558.
Intake of net energy for lactation (NE(L)) is often the limiting factor for milk production and is affected by stage of lactation and dietary concentrations of forage and fat. Because of the mechanisms involved, interactions are likely between those 2 diet components and stage of lactation. We conducted an experiment with 72 Holstein cows starting at 21 and ending at 126 d in milk (DIM). Cows were fed diets (dry matter basis) with 40 or 60% forage (67% corn silage, 33% alfalfa silage) each with 0 or 2.25% added saturated free fatty acids. The high- and low-forage diets contained 25 and 17% forage neutral detergent fiber and 30 and 33% total neutral detergent fiber, respectively; the low-forage diets contained several byproducts. Diets with and without fat contained approximately 5.2 and 3.2% long-chain fatty acids, respectively. Feeding fat or low-forage diets increased NE(L) intake, but no interaction was observed. The increase in NE(L) intake by cows fed low-forage diets was caused by increased dry matter intake, and the increase in NE(L) intake by cows fed fat was caused by increased energy density of the diet. Interactions between fat and forage were observed for energy utilization. When high-forage diets were supplemented with fat, the increased NE(L) intake went toward body energy reserves as measured by higher body condition scores with no change in milk yield. However, when low-forage diets were supplemented with fat, milk yield increased (2.6 kg/d) with no change in body condition. The differential partitioning of NE(L) may have been caused by nutrients other than NE(L) limiting milk production in cows fed the high-forage diets. With low-forage diets, intake of other nutrients was greater (i.e., greater dry matter intake). At 35 DIM, dietary treatments had little effect on milk fatty acids composition but in later lactation (125 DIM), feeding supplemental fatty acids or feeding low-forage diets increased long-chain fatty acids and decreased short-chain fatty acids. However, treatment did not have marked effects on concentrations of total fat or protein in milk. The amount of forage in a diet influences cow responses to supplemental fat and should be considered when diets are formulated.
泌乳净能（NE(L)）的摄入量通常是产奶的限制因素，受泌乳阶段和饲草料及脂肪浓度的影响。由于涉及的机制，这两种饲料成分和泌乳阶段之间可能存在相互作用。我们用 72 头荷斯坦奶牛进行了一项试验，这些奶牛从泌乳第 21 天开始，到第 126 天结束。奶牛以干物质为基础，分别饲喂 40%或 60%饲草（67%玉米青贮，33%苜蓿青贮），且每一种饲草分别添加 0 或 2.25%的饱和游离脂肪酸。高饲草和低饲草日粮的中性洗涤纤维中饲草的含量分别为 25%和 17%，总中性洗涤纤维的含量分别为 30%和 33%；低饲草日粮包含一些副产品。添加脂肪和不添加脂肪的日粮分别含有约 5.2%和 3.2%的长链脂肪酸。低饲草日粮和添加脂肪日粮都增加了泌乳净能的摄入量，但没有观察到交互作用。低饲草日粮组奶牛泌乳净能摄入量的增加是由干物质采食量的增加引起的，而脂肪日粮组奶牛泌乳净能摄入量的增加是由日粮能量密度的增加引起的。脂肪和饲草之间存在能量利用的相互作用。当高饲草日粮添加脂肪时，增加的泌乳净能摄入量被用于体能量储备，表现为体况评分增加，而产奶量没有变化。然而，当低饲草日粮添加脂肪时，产奶量增加（2.6kg/d），而体况没有变化。泌乳净能的不同分配可能是由于高饲草日粮组奶牛的其他营养素限制了产奶，而不是泌乳净能。低饲草日粮组的其他营养素摄入量较大（即干物质采食量较大）。在泌乳第 35 天，日粮处理对牛奶脂肪酸组成几乎没有影响，但在后期泌乳（125 天），添加补充脂肪或低饲草日粮增加了长链脂肪酸，减少了短链脂肪酸。然而，处理对牛奶中总脂肪或蛋白质的浓度没有显著影响。日粮中的饲草量会影响奶牛对补充脂肪的反应，在配制日粮时应加以考虑。
