Faculty of Agriculture and Life Sciences, PO Box 85084, Lincoln University, Lincoln 7647, Christchurch, New Zealand.
Faculty of Agriculture and Life Sciences, PO Box 85084, Lincoln University, Lincoln 7647, Christchurch, New Zealand.
J Dairy Sci. 2021 Jul;104(7):7696-7710. doi: 10.3168/jds.2020-19324. Epub 2021 Apr 15.
Fodder beet (FB) is a source of readily fermentable carbohydrate that can mitigate early spring herbage deficits and correct the negative energy balance experienced during early lactation in pastoral dairy systems of New Zealand. However, the low-fiber and high-soluble carbohydrate content of both FB bulb and spring herbage are factors that promote subacute ruminal acidosis, impairing rumen function and limiting the marginal milk production response to supplement. In a crossover experiment, 8 Holstein Friesian × Jersey early-lactation dairy cows were used to test the effect of supplementing 16 kg of dry matter (DM) of a grazed perennial ryegrass herbage with 6 kg of DM/d of FB bulb (FBH) versus herbage only (HO) on changes in rumen function and grazing behavior. Following 20 d of adaptation to diets, DM disappearance (%) of FB bulb (FBH cows only) and herbage were measured in sacco, separately. Cows were fasted overnight, and the ruminal contents were bailed the following morning (~0930 h) again to determine the pool size of volatile fatty acids, ammonia, and particle size of digesta, as well as to estimate the rate of ruminal outflow and degradation of neutral detergent fiber. The FBH diet did not alter DM intake, milk yield, or milk solid (fat + protein) production compared with HO. Supplementation of herbage with FB reduced ruminal pH compared with HO between ~0800 h and 1300 h each day. During each period, 1 cow experienced severe subacute ruminal acidosis (pH <5.6 for >180 min/d) during final adaptation to the target FB allocation. The FBH diet reduced the ruminal pool of acetate and ammonia, but increased the ruminal pool of butyrate and lactate compared with HO. When fed FB, rumination and grazing time increased and grazing intensity declined compared with cows fed HO. Despite increased rumination, the comminution of large particles declined 28% between the first and second rumen bailing when cows were fed FB, and in sacco DM disappearance of perennial ryegrass declined 18% compared with cows fed HO. These results indicate that grazing dairy cows supplemented with FB (40% of daily intake) increase rumination and mastication intensity to counteract reduced ruminal degradation of ryegrass herbage due to low ruminal fluid pH.
饲料甜菜（FB）是一种易发酵碳水化合物的来源，可减轻新西兰放牧奶牛系统早春草料短缺，并纠正泌乳早期的负能量平衡。然而，FB 球茎和春季草料的低纤维和高可溶性碳水化合物含量是促进亚急性瘤胃酸中毒的因素，损害瘤胃功能并限制对补充的边际牛奶生产反应。在一项交叉实验中，使用 8 头荷斯坦弗里斯兰×泽西早泌乳奶牛来测试补充 16 公斤干物质（DM）放牧多年生黑麦草草料与 6 公斤 DM/d FB 球茎（FBH）与仅草料（HO）对瘤胃功能和放牧行为变化的影响。适应饮食 20 天后，单独测量 FB 球茎（仅 FBH 奶牛）和草料的 DM 消失率（%）。奶牛隔夜禁食，次日（约 0930 h）再次抽取瘤胃液以确定挥发性脂肪酸、氨和消化物颗粒大小的池大小，以及估计瘤胃流出率和中性洗涤剂纤维的降解率。与 HO 相比，FBH 日粮并未改变 DM 摄入量、产奶量或牛奶固体（脂肪+蛋白质）产量。与 HO 相比，用 FB 补充草料可降低瘤胃 pH，每天 0800 h 至 1300 h 之间。在每个时期，1 头奶牛在最终适应目标 FB 分配时，经历了严重的亚急性瘤胃酸中毒（pH <5.6 持续> 180 min/d）。与 HO 相比，FBH 日粮减少了瘤胃中乙酸盐和氨的池，但增加了瘤胃中丁酸盐和乳酸盐的池。与喂 HO 的奶牛相比，用 FB 喂养时，反刍和放牧时间增加，放牧强度下降。尽管反刍增加，但当奶牛喂 FB 时，第一次和第二次瘤胃抽取之间大颗粒的粉碎率下降了 28%，与喂 HO 的奶牛相比，多年生黑麦草的体内 DM 消失率下降了 18%。这些结果表明，补充 FB（占每日摄入量的 40%）的放牧奶牛增加了反刍和咀嚼强度，以抵消由于低瘤胃液 pH 导致多年生黑麦草草料瘤胃降解减少。
