Department of Animal Biosciences, University of Guelph, Guelph, Ontario, N1G 2W1, Canada.
Department of Population Medicine, University of Guelph, Guelph, Ontario, N1G 2W1, Canada.
J Dairy Sci. 2019 Jan;102(1):652-659. doi: 10.3168/jds.2018-15064. Epub 2018 Nov 15.
The objective of this study was to determine if the risk of developing subacute ruminal acidosis, as potentially affected by dietary straw particle size, influenced the feed sorting, rumination behavior, and milk production of early lactation dairy cows. Upon calving, 41 multiparous Holstein cows were fed a total mixed ration with 9% wheat straw (dry matter basis) chopped (1) using a 2.54-cm screen (short; n = 21) or (2) using a 5.08-cm screen (long; n = 20). For the first 4 wk following calving, rumination behavior (recorded using data loggers attached to neck collars) and reticulorumen pH (recorded using wireless telemetry boluses) were monitored 24 h/d. Due to technical failures, analyses were conducted on 38 cows (n = 19 per treatment). Total mixed ration and orts samples were collected every 3 d to determine feed sorting. Based on an acidosis index, created using area under the curve data (reticulorumen pH < 5.8) normalized for dry matter intake, cows were categorized as either low (LR) or high (HR) risk for developing subacute ruminal acidosis (SARA). Low risk cows had higher mean (6.3 vs. 6.1), minimum (6.0 vs. 5.7), and maximum (6.7 vs. 6.5) reticulorumen pH than HR cows. Low risk cows also had less severe area under the curve values (1.5 vs. 49.4 pH × min/d) and spent less time below a reticulorumen pH threshold of 5.8 (21.9 vs. 309.2 min/d). Although total milk yield was unaffected by SARA risk, LR cows produced more 4% fat-corrected milk (47.2 vs. 41.9 kg/d) and milk fat (2.1 vs. 1.8 kg/d) than HR cows. A SARA risk category × treatment interaction was detected for sorting all fractions of the diet; HR cows on the long treatment sorted against the longest particles in the diet, whereas LR cows on the same treatment did not sort this fraction, suggesting that SARA risk may be mitigated by a more balanced intake of physically effective fiber. High risk cows on the short treatment consumed the longest dietary particles as predicted, and sorted in favor of the physically effective medium and short particles. A SARA risk category × treatment interaction was detected for rumination behavior; within the long treatment, HR cows tended to ruminate less than LR cows (432.3 vs. 493.2 min/d). Overall, these results suggest that LR cows consumed a more balanced diet, whereas HR cows sorted their feed more, particularly when fed the diet containing long straw particles, which may have led to reduced rumination activity and yield of milk fat and fat-corrected milk.
本研究旨在确定亚急性瘤胃酸中毒的发病风险（可能受饲粮中秸秆颗粒大小的影响）是否会影响奶牛产犊后的采食行为、反刍行为和产奶性能。在产犊后，41 头经产荷斯坦奶牛饲喂了含有 9%小麦秸秆（干物质基础）的全混合日粮，其中 21 头奶牛的秸秆采用 2.54 厘米筛片切碎（短；n=21），20 头奶牛的秸秆采用 5.08 厘米筛片切碎（长；n=20）。在产犊后的前 4 周，使用颈圈上的记录仪（24 小时记录）监测反刍行为，使用无线遥测丸剂（每 2 小时记录）监测瘤胃 pH 值。由于技术故障，仅对 38 头奶牛（n=19 头/处理）进行了分析。每 3 天收集一次全混合日粮和饲槽剩余物，以确定饲料的选择情况。根据采用曲线下面积（reticulorumen pH < 5.8）数据创建的酸中毒指数，将奶牛分为低（LR）或高（HR）亚急性瘤胃酸中毒（SARA）发病风险。低风险奶牛的平均（6.3 比 6.1）、最小（6.0 比 5.7）和最大（6.7 比 6.5）瘤胃 pH 值均高于高风险奶牛。低风险奶牛的曲线下面积值也较低（1.5 比 49.4 pH×min/d），瘤胃 pH 值低于 5.8 的时间也较少（21.9 比 309.2 min/d）。尽管 SARA 风险对总产奶量没有影响，但低风险奶牛的 4%脂肪校正奶（47.2 比 41.9 kg/d）和乳脂（2.1 比 1.8 kg/d）产量更高。在所有饲料部分的选择上，均检测到 SARA 风险类别×处理的互作；长处理组的高风险奶牛对饲粮中最长的颗粒进行了挑食，而同一处理组的低风险奶牛则没有进行挑食，这表明 SARA 风险可能通过更平衡地摄入物理有效纤维得到缓解。短处理组的高风险奶牛如预测的那样摄入了最长的饲粮颗粒，并对物理有效中短颗粒进行了挑食。在反刍行为方面，也检测到了 SARA 风险类别×处理的互作；在长处理组中，高风险奶牛的反刍时间倾向于低于低风险奶牛（432.3 比 493.2 min/d）。总的来说，这些结果表明，低风险奶牛的饲料更平衡，而高风险奶牛的挑食更严重，尤其是在饲喂含有长秸秆颗粒的日粮时，这可能导致反刍活动减少，乳脂和脂肪校正奶产量降低。
