Universidade Federal de Lavras, Lavras, MG 37200-000, Brazil.
Universidade Federal de Lavras, Lavras, MG 37200-000, Brazil; Better Nature Research Center, Ijaci, MG 37218-000, Brazil.
J Dairy Sci. 2019 Nov;102(11):9857-9869. doi: 10.3168/jds.2019-16559. Epub 2019 Sep 11.
Rehydrated and ensiled mature ground corn has high ruminal starch digestibility, but particle size (PS) and dietary starch proportion (ST) can affect starch digestion and lactating cow performance. We evaluated the effect of rehydrated and ensiled corn (REC), PS, and ST on intake, lactation performance, nutrient digestibility, ruminal fermentation profile, and chewing behavior of dairy cows. Kernels from an 84% vitreousness hybrid were finely (FN) or coarsely (CS) ground, yielding geometric mean particle sizes of 1,591 and 2,185 µm, respectively. Ground kernels were rehydrated [60% dry matter (DM)] and ensiled in 200-L buckets for ≥205 d. The grinding rate (t/h) was 3.9 for FN and 11.7 for CS. The PS did not affect DM loss (11.3% of ensiled) or silage pH (3.8). Samples of each bucket (n = 15/PS) before and after silage fermentation were incubated in situ for 0, 3, 6, 18, and 48 h in 4 rumen-cannulated lactating cows. Ensiling increased the effective ruminal in situ DM degradation (63.7 vs. 34.1%), regardless of PS. Sixteen Holstein cows (152 ± 96 d in milk) in 4 × 4 Latin squares (21-d periods) were individually fed a 2 × 2 factorial combination of low (LO) or high (HI) starch diets with FN or CS. Cows were fed the same REC incubated in situ. Varied concentration of starch in the diet (29.2 vs. 23.5% of DM) was achieved by partial replacement of REC (22.0 vs. 14.2% of DM) with citrus pulp (0 vs. 8.2% of DM). Milk, protein, fat, and lactose yields did not differ. Milk fat percentage was reduced and protein percentage was increased by HI. Treatment FN increased feed efficiency (energy-corrected milk/digestible organic matter intake) when fed with HI. Total-tract starch digestibility tended to be reduced by CS (96.4 vs. 97.2% of starch intake). Serum β-hydroxybutyrate was increased by LO. High-starch diet reduced the molar proportions of acetate and butyrate in ruminal fluid and increased propionate and isoacids. Particle size did not affect ruminal fermentation profile. Coarse grinding reduced plasma d-lactate concentration with HI. Diet HI reduced the proportion of daily intake from 1900 to 0700 h and induced preferential intake of feed particles <8 mm and greater refusal of particles >19 mm in the morning. Fine REC reduced rumination time per day and increased eating time per DM intake. Milk and plasma urea-N did not differ. Ensiling of mature flint corn for >200 d largely eliminated the effect of the PS of REC on the studied outcomes. The proportion of REC in the diet affected ruminal fermentation profile and milk solids concentration, but did not affect short-term performance and digestibility. Coarse grinding of REC may allow increasing the grinding rate and thus save labor and energy during ensiling.
水合青贮成熟马齿型玉米具有较高的瘤胃淀粉消化率，但颗粒大小（PS）和日粮淀粉比例（ST）会影响淀粉消化和泌乳牛的生产性能。我们评估了水合青贮成熟马齿型玉米（REC）、PS 和 ST 对奶牛采食量、泌乳性能、养分消化率、瘤胃发酵特性和咀嚼行为的影响。采用一种 84%玻璃质杂交种，将玉米籽粒进行细粉碎（FN）或粗粉碎（CS），得到的几何平均粒径分别为 1591μm 和 2185μm。粉碎后的玉米籽粒经水合（干物质含量 60%）并在 200-L 桶中青贮 205d 以上。FN 的粉碎速率（t/h）为 3.9，CS 为 11.7。PS 对 DM 损失（青贮物中 11.3%）或青贮物 pH（3.8）没有影响。在青贮发酵前后，从每个桶中（PS 各 15 个样本）取出样品，在 4 头瘤胃瘘管泌乳奶牛中进行原位培养 0、3、6、18 和 48h。青贮处理增加了有效瘤胃 DM 降解率（63.7% vs. 34.1%），与 PS 无关。在 4×4 拉丁方试验中，16 头荷斯坦奶牛（泌乳 152±96d）分别饲喂低（LO）或高（HI）淀粉日粮，日粮中的淀粉浓度（29.2% vs. 23.5%DM）通过部分用柑橘渣（0% vs. 8.2%DM）替代 REC（22.0% vs. 14.2%DM）来实现。奶牛饲喂相同的 REC 进行原位发酵。HI 处理增加了饲料效率（校正能量奶/可消化有机物采食量）。与 FN 相比，CS 处理降低了总消化道淀粉消化率（96.4% vs. 97.2%的淀粉摄入量）。CS 处理增加了血清β-羟丁酸。高淀粉日粮降低了瘤胃液中乙酸和丁酸的摩尔比例，增加了丙酸和异丁酸。PS 不影响瘤胃发酵特性。HI 处理降低了血浆 d-乳酸水平。HI 日粮降低了 1900 到 0700h 的日采食量比例，并导致奶牛在早上更倾向于采食＜8mm 的饲料颗粒，而拒绝＞19mm 的颗粒。细粉碎的 REC 减少了奶牛的每日反刍时间，增加了每摄入 1kgDM 的采食时间。牛奶和血浆尿素氮没有差异。成熟硬质玉米青贮 200d 以上，基本消除了 REC 的 PS 对研究结果的影响。日粮中 REC 的比例影响瘤胃发酵特性和牛奶固体浓度，但不影响短期生产性能和消化率。粗粉碎 REC 可能会增加粉碎速率，从而在青贮过程中节省劳动力和能源。
