Wheat is the most common concentrate fed to grazing dairy cows in Australia, but no studies have examined the effects of wheat proportion in a pasture-based diet on milk production and methane emissions. In this 47-d experiment, 32 Holstein dairy cows were offered 1 of 4 diets during d 1 to 36. Cows in each of the dietary treatment groups were individually offered no wheat (W0) or wheat at 3 kg of dry matter (DM)/d (W3), 6 kg of DM/d (W6), or 9 kg of DM/d (W9). The remainder of the diet was 2.2 kg of DM of concentrate mix and freshly harvested perennial ryegrass (Lolium perenne) such that all individual cows were offered a total diet of approximately 20.2 kg of DM/d. From d 37 to 47 the diets of cows receiving treatments W0 and W3 remained unchanged, but cows in treatments W6 and W9 received the W3 diet. Individual cow feed intakes, milk yields, milk compositions, and methane emissions were measured for d 31 to 35 (period 1) and d 45 to 47 (period 2). During period 1, the mean intakes of cows offered the W0, W3, W6, and W9 diets were 19.2, 20.4, 20.2, and 19.8 kg of DM/d. Diet caused differences in energy-corrected milk, and means for W0, W3, W6, and W9 were 29.5, 32.4, 33.0, and 32.9 kg/d, respectively. Milk fat percentage differed with respective means of 3.93, 3.94, 3.69, and 3.17. Diets also caused differences in methane emissions, with means for W0, W3, W6, and W9 of 440, 431, 414, and 319 g/d. During period 1, the cows fed the W9 diet produced less methane and had lower methane yields (g/kg of DMI) and intensities (g/kg of energy-corrected milk) than cows fed the W3 diet. However, in period 2 when the wheat intake of cows in the W9 treatment was reduced to the same level as in the W3 treatment, their methane emissions, yields, and intensities were similar to those offered the W3 treatment, yet protozoa numbers in ruminal fluid were still much lower than those in cows offered the W3 treatment. Our research shows that for diets based on perennial ryegrass and crushed wheat, only the diet containing more than 30% crushed wheat resulted in substantially depressed milk fat concentration and reduced methane emissions, methane yield, and methane intensity. Thus, although feeding a diet with a high proportion of wheat can cause substantial methane mitigation, it can come at the cost of depression in milk fat concentration.

中文翻译：

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牧场饮食中小麦的比例对奶牛产奶量，甲烷排放量，甲烷产量和瘤胃原生动物的影响。

小麦是澳大利亚放牧奶牛中最常见的浓缩饲料，但尚无研究检查牧场饮食中小麦比例对牛奶产量和甲烷排放的影响。在这个47天的实验中，在第1到36天的第4天中，有32头荷斯坦奶牛获得了饲料。每个饮食处理组中的母牛均没有小麦（W0）或3千克干物质（DM）的小麦/ d（W3），6 kg DM / d（W6）或9 kg DM / d（W9）。日粮的其余部分为2.2千克干物质的DM干粉和新鲜收获的多年生黑麦草（黑麦草），因此，所有单头母牛的总日粮摄入量约为20.2千克干物质/天。从第37天到47天，接受处理W0和W3的母牛的日粮保持不变，但接受处理W6和W9的母牛的日粮为W3。个体母牛的采食量，牛奶产量，在d 31至35（时段1）和d 45至47（时段2）中测量了牛奶成分和甲烷排放量。在第1阶段，提供W0，W3，W6和W9日粮的奶牛平均摄入量为19.2、20.4、20.2和19.8千克DM / d。饮食导致能量校正后的牛奶存在差异，W0，W3，W6和W9的平均值分别为29.5、32.4、33.0和32.9 kg / d。牛奶脂肪百分比的平均值分别为3.93、3.94、3.69和3.17。日粮还造成甲烷排放量的差异，W0，W3，W6和W9的平均值分别为440、431、414和319 g / d。在第1阶段，与饲喂W3日粮的母牛相比，饲喂W9日粮的母牛产生的甲烷更少，甲烷产量（g / kg DMI）和强度（g / kg能量校正的牛奶）更低。然而，在第2阶段，当W9处理的母牛的小麦摄入量减少到与W3处理相同的水平时，它们的甲烷排放量，产量和强度与W3处理相似，但是瘤胃液中的原生动物数量仍然远低于提供W3处理的母牛。我们的研究表明，对于以多年生黑麦草和压碎小麦为基础的日粮，只有含压碎小麦超过30％的日粮才能显着降低乳脂浓度，并降低甲烷排放量，甲烷产量和甲烷强度。因此，尽管以高比例的小麦喂养饮食可以显着减轻甲烷含量，但它可能以降低乳脂浓度为代价。然而，瘤胃液中的原生动物数量仍远低于接受W3处理的母牛。我们的研究表明，对于以多年生黑麦草和压碎小麦为基础的日粮，只有含压碎小麦超过30％的日粮才能显着降低乳脂浓度，并降低甲烷排放量，甲烷产量和甲烷强度。因此，尽管以高比例的小麦喂养饮食可以显着减轻甲烷含量，但它可能以降低乳脂浓度为代价。然而，瘤胃液中的原生动物数量仍远低于接受W3处理的母牛。我们的研究表明，对于以多年生黑麦草和压碎小麦为基础的日粮，只有含压碎小麦超过30％的日粮才能显着降低乳脂浓度，并降低甲烷排放量，甲烷产量和甲烷强度。因此，尽管以高比例的小麦喂养饮食可以显着减轻甲烷含量，但它可能以降低乳脂浓度为代价。只有含有超过30％的压碎小麦的饮食才能使牛奶中的脂肪浓度大大降低，并减少甲烷排放，甲烷产量和甲烷强度。因此，尽管以高比例的小麦喂养饮食可以显着减轻甲烷含量，但它可能以降低乳脂浓度为代价。只有含有超过30％的压碎小麦的饮食才能使牛奶中的脂肪浓度大大降低，并减少甲烷排放，甲烷产量和甲烷强度。因此，尽管以高比例的小麦喂养饮食可以显着减轻甲烷含量，但它可能以降低乳脂浓度为代价。