物理有效未降解中性洗涤纤维与泌乳荷斯坦奶牛日粮中瘤胃可发酵淀粉之间的关系

摘要(中文译文)

我们评估了在体外发酵240小时后物理有效未降解中性洗涤纤维（peuNDF240）含量较低或中等的日粮中，瘤胃可发酵淀粉（RFS；7小时体外淀粉消化率）对干物质采食量（DMI）、产奶量及乳成分、咀嚼行为、瘤胃功能以及表观全消化道养分消化率的影响。选取16头泌乳期荷斯坦奶牛（其中8头安装瘤胃瘘管），平均泌乳天数为85 ± 15（标准差），采用重复4 × 4拉丁方设计（每期28天），以2 × 2析因安排处理。日粮通过加入棕色中脉或常规玉米青贮以及调整粉碎玉米与甜菜粕的相对比例来改变peuNDF240和RFS含量。peuNDF240的测定方法为：日粮物理有效部分（干式垂直筛分后保留在≥1.18 mm筛上的颗粒）经240小时体外发酵后的未降解NDF（uNDF240）含量。所有日粮的uNDF240含量均较低（约占干物质的7%），但在中等peuNDF240日粮中，其分布偏向较粗的颗粒。日粮实测组成如下：（1）低peuNDF240（占干物质6.4%）、低RFS（占干物质16.7%）；（2）低peuNDF240（占干物质6.1%）、中等RFS（占干物质19.2%）；（3）中等peuNDF240（占干物质8.6%）、低RFS（占干物质16.9%）；（4）中等peuNDF240（占干物质8.0%）、中等RFS（占干物质19.0%）。奶牛饲养于拴系式牛舍，每日饲喂一次全混合日粮（TMR），每日挤奶3次。数据采用SAS（9.4版，SAS Institute Inc.，Cary，NC）的MIXED程序，按重复拉丁方设计中的析因安排进行分析。模型包含RFS、peuNDF240、RFS × peuNDF240、重复方内时期和方的固定效应。方内的奶牛作为随机效应进行检验。在采食量、泌乳性能和瘤胃特征指标方面，peuNDF240与RFS之间几乎没有交互作用。饲喂低peuNDF240日粮的奶牛干物质采食量高于饲喂中等peuNDF240日粮的奶牛。正如预期，中等peuNDF240日粮导致更高的uNDF240摄入量，而中等RFS日粮提高了淀粉摄入量。饲喂中等RFS日粮的奶牛产奶乳脂量和3.5%乳脂校正乳（FCM）产量低于饲喂低RFS日粮的奶牛。低peuNDF240日粮导致乳脂中混合来源脂肪酸较少，不饱和度较高。与此相关，与低RFS相比，中等RFS日粮倾向于降低FCM生产效率（FCM/DMI）。采食时间不受日粮影响，但在低peuNDF240条件下，中等RFS日粮促进了反刍活动。此外，中等RFS日粮缩短了单次采食时长并增加了每日采食次数。与乳脂变化一致，低RFS日粮提高了乙酸：丙酸比例，而低peuNDF240日粮降低了支链挥发性脂肪酸（VFA）的摩尔比例。日粮对瘤胃pH指标无影响。正如预期，中等日粮RFS倾向于增加瘤胃淀粉池大小，中等peuNDF240增加了uNDF240池大小，尽管日粮对瘤胃淀粉或uNDF240周转的影响甚微。低peuNDF240日粮的表观全消化道NDF消化率高于中等peuNDF240日粮。当给泌乳奶牛饲喂低peuNDF240日粮时，即使饲喂中等水平的日粮RFS也会降低乳脂产量。

Abstract

We assessed the effect of rumen-fermentable starch (RFS; 7-h in vitro starch digestibility) in diets that contained low or moderate physically effective undegraded NDF after 240-h of in vitro fermentation (peuNDF240) on DMI, milk yield and composition, chewing behavior, ruminal function, and apparent total-tract nutrient digestibility. Sixteen lactating Holstein cows (8 ruminally cannulated) averaging 85 ± 15 (SD) DIM were enrolled in a replicated 4 × 4 Latin square design (28-d periods) with a 2 × 2 factorial arrangement of treatments. Diets differed in peuNDF240 and RFS content by inclusion of either brown midrib or conventional corn silage and by varying relative proportions of ground corn and beet pulp. The peuNDF240 was measured as undegraded NDF after 240 h of in vitro fermentation (uNDF240) content of the physically effective fraction of the diet (particles retained on ≥1.18-mm screen with dry vertical sieving). All diets contained low uNDF240 (∼7% of DM), but its distribution was skewed to coarser particles for the moderate peuNDF240 diets. The Analyzed composition of diets was as follows: (1) low peuNDF240 (6.4% of DM), low RFS (16.7% of DM); (2) low peuNDF240 (6.1% of DM), moderate RFS (19.2% of DM); (3) moderate peuNDF240 (8.6% of DM), low RFS (16.9% of DM); and (4) moderate peuNDF240 (8.0% of DM), moderate RFS (19.0% of DM). Cows were housed in tiestalls, fed TMR once daily, and milked 3 times daily. Data were analyzed as a factorial arrangement of treatments within a replicated Latin square design using the MIXED procedure of SAS (version 9.4, SAS Institute Inc., Cary, NC). Model included fixed effects of RFS, peuNDF240, RFS × peuNDF240, period within replicated square, and square. Cow within square was tested as a random effect. Few interactions existed between peuNDF240 and RFS for measures of intake, lactation performance, and ruminal characteristics. Cows fed low peuNDF240 diets consumed more DM than cows fed moderate peuNDF240. As expected, moderate peuNDF240 diets resulted in greater uNDF240 intake, whereas moderate RFS diets boosted starch intake. Cows fed diets containing moderate RFS produced less milk fat and 3.5% FCM than cows fed low RFS. Low-peuNDF240 diets resulted in fewer mixed origin fatty acids in milk fat and greater degree of unsaturation. Relatedly, moderate-RFS diets tended to reduce efficiency of FCM production (FCM/DMI) compared with low RFS. Eating time was unaffected by diet, but with low peuNDF240, diets of moderate RFS boosted rumination activity. Additionally, moderate-RFS diets reduced meal length and increased daily meal bouts. Consistent with changes in milk fat, low-RFS diets increased acetate:propionate ratio, whereas low-peuNDF240 diets reduced molar proportions of branched-chain VFA. Diet had no effect on measures of ruminal pH. As expected, moderate dietary RFS tended to increase ruminal pool size of starch, and moderate peuNDF240 increased pool size of uNDF240, although there were few dietary effects on ruminal turnover of starch or uNDF240. Low-peuNDF240 diets resulted in greater apparent total-tract NDF digestibility than moderate peuNDF240. Feeding even moderate dietary RFS depresses milk fat output when low-peuNDF240 diets are fed to lactating dairy cows.

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