Kahyani A, Ghorbani G R, Khorvash M, Nasrollahi S M, Beauchemin K A
Department of Animal Sciences, Isfahan University of Technology, Isfahan 84156-83111, Iran.
Research Centre, Agriculture and Agri-Food Canada, Lethbridge, AB, Canada T1J 4B1.
J Dairy Sci. 2013;96(11):7110-7119. doi: 10.3168/jds.2012-6462. Epub 2013 Sep 18.
This study evaluated the effects of increasing the physically effective neutral detergent fiber (peNDF) intake of lactating dairy cows fed high-concentrate diets supplemented with unsaturated fat on intake, eating behavior, diet sorting, chewing activity, total-tract digestibility, and milk production and composition. Diets contained 24% alfalfa hay (AH), 16% corn silage, 58% concentrate, and 2% yellow grease [dry matter (DM) basis], and dietary peNDF content was increased by varying the particle size (PS) of the AH. Nine multiparous cows averaging 87.8 ± 14.8d in milk and weighing 653 ± 53 kg were randomly assigned to a triplicate 3 × 3 Latin square. During each 21-d period, cows were offered 1 of 3 total mixed rations that varied in PS of AH: fine, medium, and long, with a geometric mean particle length of 3.00, 3.57 and 3.87 mm, respectively. Increasing PS quadratically affected DM intake (DMI; 24.7, 25.4, and 23.7 kg/d, for fine, medium, and long, respectively), but cumulative DMI at 2, 4, and 6h after feeding was similar across treatments, averaging 23.4, 35.6 and 46.4% of total DMI for the 3 time points, respectively. Increased peNDF intake did not affect feed sorting, but increased daily eating time, and eating and total chewing time per kilogram of DMI. Daily rumination time exhibited a quadratic response, with highest rumination time for the medium diet. Dietary PS had no effects on digestibility in the total tract, but we observed, for fine, medium, and long diets, quadratic responses in milk production (41.5, 43.3, and 40.4 kg/d), 4% fat-corrected milk production, and milk protein yield. Milk fat content decreased linearly with increasing PS, but milk fat content and fat:protein ratio were low for all treatments, likely due to adding unsaturated fat to a diet containing a high level of nonfiber carbohydrates (42.2% of DM). The composition, degree of saturation, and total conjugated linoleic acid content of fatty acids in milk fat were not affected by the change in peNDF content of the diet. The study indicates that a moderate increase in the PS of AH in diets containing unsaturated fat elevates peNDF intake and increases chewing activity, DMI, milk yield and milk fat production. However, the effects of dietary PS were quadratic, with maximum DMI and milk production observed with diets supplying 24% dietary peNDF (measured as the proportion of the ration retained on sieves >1.18 mm multiplied by dietary neutral detergent fiber content; DM basis).
本研究评估了增加采食高浓度日粮并补充不饱和脂肪的泌乳奶牛的物理有效中性洗涤纤维（peNDF）摄入量，对其采食量、采食行为、日粮分选、咀嚼活动、全消化道消化率、产奶量及乳成分的影响。日粮包含24%苜蓿干草（AH）、16%玉米青贮、58%精料以及2%黄色油脂（基于干物质[DM]），通过改变AH的粒度（PS）来提高日粮peNDF含量。9头经产奶牛，平均泌乳87.8±14.8天，体重653±53千克，被随机分配至一个重复3次的3×3拉丁方试验。在每个21天周期内，给奶牛提供3种全混合日粮中的1种，这些日粮的AH粒度不同：细粒度、中等粒度和长粒度，几何平均颗粒长度分别为3.00、3.57和3.87毫米。增加PS呈二次方影响干物质采食量（DMI；细粒度、中等粒度和长粒度分别为24.7、25.4和23.7千克/天），但采食后2、4和6小时的累积DMI在各处理间相似，3个时间点分别平均占总DMI的23.4%、35.6%和46.4%。增加peNDF摄入量不影响日粮分选，但增加了每日采食时间以及每千克DMI的采食和总咀嚼时间。每日反刍时间呈二次方响应，中等粒度日粮的反刍时间最长。日粮PS对全消化道消化率无影响，但我们观察到，细粒度、中等粒度和长粒度日粮在产奶量（41.5、43.3和40.4千克/天）、4%乳脂校正乳产量和乳蛋白产量方面呈二次方响应。乳脂肪含量随PS增加呈线性下降，但所有处理的乳脂肪含量和脂肪:蛋白比均较低，这可能是由于在含有高水平非纤维碳水化合物（占DM的42.2%）的日粮中添加了不饱和脂肪。日粮peNDF含量的变化不影响乳脂肪中脂肪酸的组成、饱和度及总共轭亚油酸含量。该研究表明，在含有不饱和脂肪的日粮中适度增加AH的PS可提高peNDF摄入量，并增加咀嚼活动、DMI、产奶量和乳脂肪产量。然而，日粮PS的影响呈二次方，在提供24%日粮peNDF（通过筛孔>1.18毫米留存日粮比例乘以日粮中性洗涤纤维含量来衡量；基于DM）的日粮中观察到最大DMI和产奶量。
