Centre for Dairy Research, School of Agriculture, Policy and Development, University of Reading, PO Box 237, Earley Gate, Reading, RG6 6AR, United Kingdom.
Centre for Dairy Research, School of Agriculture, Policy and Development, University of Reading, PO Box 237, Earley Gate, Reading, RG6 6AR, United Kingdom.
J Dairy Sci. 2017 Sep;100(9):7127-7138. doi: 10.3168/jds.2017-12914. Epub 2017 Jul 6.
The objective of this study was to investigate whether higher lucerne (Medicago sativa; alfalfa) silage inclusion rate and longer lucerne chop length improves rumen function through increased provision of physically effective fiber, when included in a maize and lucerne silage-based total mixed ration. Diets were formulated to contain a 50:50 forage:concentrate ratio [dry matter (DM) basis] and be isonitrogenous and contain equal levels of neutral detergent fiber (320 g/kg). The forage portion of the offered diets was composed of maize and lucerne silage DM in proportions (wt/wt) of either 25:75 (high lucerne; HL) or 75:25 (low lucerne; LL). Second-cut lucerne was harvested and conserved as silage at either a long (L) or a short (S) chop length (geometric mean particle lengths of 9.0 and 14.3 mm, respectively). These variables were combined in a 2 × 2 factorial arrangement to give 4 treatments (HLL, HLS, LLL, LLS), which were fed in a 4 × 4 Latin square design study to 4 rumen-cannulated, multiparous, Holstein dairy cows in mid lactation. Effects on DM intake, chewing behavior, rumen volatile fatty acid concentration, rumen pH, rumen and fecal particle size, milk production, and milk fatty acid profile were measured. Longer chop length increased rumination times per kilogram of DM intake (+2.8 min/kg) relative to the S chop length, with HLL diets resulting in the most rumination chews. Rumen concentrations of total volatile fatty acids, acetate, and n-valerate were higher for the HLS diet than the other 3 diets, whereas rumen propionate concentration was lowest for the HLL diet. Physically effective fiber (particles >4 mm) percentage in the rumen mat was increased when L chop length was fed regardless of lucerne inclusion rate. No effect of treatment was observed for milk yield, although milk protein concentration was increased by L for the LL diet (+1.6 g/kg) and decreased by L for the HLL diet (-1.4 g/kg). Milk fat concentrations of total cis-18:1 (+3.7 g/100 g of fatty acids) and 18:3 n-3 (+0.2 g/100 g of fatty acids) were greater with HL. In conclusion, longer lucerne silage chop length increased time spent ruminating per kilogram of DM intake, but had no effect on rumen pH in the present study. Increasing dietary lucerne inclusion rate had no effects on rumination activity or rumen pH, but decreased the ratio of n-6:n-3 polyunsaturated fatty acid concentrations in milk fat.
本研究旨在探讨在以玉米和紫花苜蓿青贮为基础的全混合日粮中，提高紫花苜蓿青贮的添加率和紫花苜蓿切短长度，是否能通过提供更多物理有效纤维来改善瘤胃功能。日粮的配方为干物质（DM）基础上含有 50:50 的粗饲料：精料比[和等氮水平，并含有等量的中性洗涤纤维（320 g/kg）。提供的日粮的粗饲料部分由玉米青贮和紫花苜蓿青贮 DM 组成，比例为 25:75（高紫花苜蓿；HL）或 75:25（低紫花苜蓿；LL）。第二茬紫花苜蓿收获并青贮为长切（L）或短切（S）（几何平均粒径分别为 9.0 和 14.3mm）。这些变量以 2×2 析因设计组合，得到 4 种处理（HLL、HLS、LLL、LLS），在泌乳中期的 4 头瘤胃切开、多胎、荷斯坦奶牛中以 4×4 拉丁方设计进行试验。测定了 DM 摄入量、咀嚼行为、瘤胃挥发性脂肪酸浓度、瘤胃 pH 值、瘤胃和粪便颗粒大小、产奶量和牛奶脂肪酸组成。与 S 切短长度相比，较长的切短长度使每千克 DM 摄入量的反刍时间增加（+2.8 分钟/千克），而 HLL 日粮导致的反刍咀嚼次数最多。与其他 3 种日粮相比，HLS 日粮的总挥发性脂肪酸、乙酸和正戊酸浓度较高，而 HLL 日粮的丙酸浓度最低。无论紫花苜蓿添加率如何，使用 L 切短长度均可增加瘤胃基质中物理有效纤维（>4mm 颗粒）的百分比。尽管 L 对 LL 日粮的牛奶蛋白浓度（+1.6 g/kg）有增加作用，而对 HLL 日粮有降低作用（-1.4 g/kg），但处理对产奶量没有影响。总顺式-18:1（+3.7 g/100 g 脂肪酸）和 18:3n-3（+0.2 g/100 g 脂肪酸）的牛奶脂肪浓度随着 HL 的增加而增加。总之，较长的紫花苜蓿青贮切短长度增加了每千克 DM 摄入量的反刍时间，但在本研究中对瘤胃 pH 没有影响。增加日粮中紫花苜蓿的添加率对反刍活动或瘤胃 pH 没有影响，但降低了牛奶脂肪中 n-6:n-3 多不饱和脂肪酸浓度的比值。
