Jiang F G, Lin X Y, Yan Z G, Hu Z Y, Liu G M, Sun Y D, Liu X W, Wang Z H
Ruminant Nutrition and Physiology Laboratory, College of Animal Science and Technology, Shandong Agricultural University, Taian 271018, P. R. China.
Institute of Qingdao Animal Husbandry and Veterinary Research, Qingdao 266000, P. R. China.
J Dairy Sci. 2017 Apr;100(4):2660-2671. doi: 10.3168/jds.2016-11559. Epub 2017 Feb 16.
Increasing dietary roughage level is a commonly used strategy to prevent subacute ruminal acidosis. We hypothesized that high-roughage diets could promote chewing activity, saliva secretion, and hence more alkaline to buffer rumen pH. To verify the hypothesis, 12 multiparous Holstein cows in mid lactation were randomly allocated to 4 treatments in a triplicated 4 × 4 Latin square experiment with one cow in each treatment surgically fitted with a ruminal cannula. Treatments were diets containing 40, 50, 60, or 70% of roughage on a DM basis. Increasing dietary roughage level decreased DM, CP, OM, starch, and NE intake, increased ADF intake, and decreased milk yield linearly. Intake of NDF was quite stable across treatments and ranged from 7.8 to 8.1 kg/d per cow. Daily eating time increased linearly with increased roughage level. The increase in eating time was due to increased eating time per meal but not number of meals per day, which was stable and ranged from 8.3 to 8.5 meals per day across treatments. Increasing dietary roughage level had no effect on ruminating time (min/d), the number of ruminating periods (rumination periods per d), and chewing time per ruminating period (min/ruminating period). Ruminating time per kilogram of NDF intake and total chewing time per kilogram of ADF intake were similar across treatments (57.4 and 183.8 min/kg, respectively). Increasing dietary roughage level linearly increased daily total chewing time; linearly elevated the mean, maximum, and minimum ruminal pH; and linearly decreased total VFA concentration and molar proportion of propionate in ruminal fluid. Saliva secretion during eating was increased, the secretion during rumination was unaffected, but the secretion during resting tended to decrease with increased dietary roughage level. As a result, total saliva secretion was not affected by treatments. In conclusion, the results of the present study did not support the concept that high-roughage diets elevated ruminal pH through increased salivary recycling of buffering substrates.
提高日粮粗饲料水平是预防亚急性瘤胃酸中毒常用的策略。我们假设高粗饲料日粮可以促进咀嚼活动、唾液分泌，从而产生更多的碱来缓冲瘤胃pH值。为验证该假设，在一项重复的4×4拉丁方试验中，将12头处于泌乳中期的经产荷斯坦奶牛随机分为4组处理，每组处理中有1头奶牛通过手术安装瘤胃瘘管。处理日粮的干物质基础上粗饲料含量分别为40%、50%、60%或70%。提高日粮粗饲料水平使干物质、粗蛋白、有机物、淀粉和净能摄入量呈线性下降，酸性洗涤纤维摄入量增加，产奶量呈线性下降。中性洗涤纤维摄入量在各处理间相当稳定，每头奶牛每天为7.8至8.1千克。每日采食时间随粗饲料水平升高呈线性增加。采食时间的增加是由于每餐采食时间增加，而非每日采食次数增加，采食次数稳定，各处理间为每天8.3至8.5次。提高日粮粗饲料水平对反刍时间（分钟/天）、反刍周期数（反刍周期数/天）和每个反刍周期的咀嚼时间（分钟/反刍周期）没有影响。每千克中性洗涤纤维摄入量的反刍时间和每千克酸性洗涤纤维摄入量的总咀嚼时间在各处理间相似（分别为57.4和183.8分钟/千克）。提高日粮粗饲料水平使每日总咀嚼时间呈线性增加；使瘤胃pH值的平均值、最大值和最小值呈线性升高；使瘤胃液中总挥发性脂肪酸浓度和丙酸摩尔比例呈线性下降。采食期间的唾液分泌增加，反刍期间的分泌不受影响，但随着日粮粗饲料水平升高，休息期间的分泌趋于减少。因此，总唾液分泌不受处理的影响。总之，本研究结果不支持高粗饲料日粮通过增加缓冲底物的唾液再循环来提高瘤胃pH值这一概念。
