Gregorini P, Gunter S A, Beck P A
Southwest Research and Extensions Center, Division of Agriculture, University of Arkansas, Hope 71801, USA.
J Anim Sci. 2008 Apr;86(4):1006-20. doi: 10.2527/jas.2007-0432. Epub 2008 Jan 11.
This work aimed to assess the impact of timing of herbage allocation and fasting on patterns of ingestive behavior, herbage intake, ruminal fermentation, nutrient flow to the duodenum, and site and extent of digestion. Treatments were daily herbage allocation in the afternoon (1500 h, AHA), morning (0800 h, MHA), AHA after 20 h of fasting (AHAF), and MHA after 20 h of fasting (MHAF). Four ruminally and duodenally fistulated heifers (279 +/- 99 kg of BW) individually strip-grazed wheat pastures in a Latin-square design. Eating, rumination, and idling behavior were recorded every 2 min, and bite and eating step rates were measured hourly while the heifers were grazing (11 h MHA and AHA; 4 h MHAF and AHAF). Ruminal DM pools were measured 4 times daily (0800, 1200, 1500, and 1900 h) to estimate daily herbage DMI and its pattern. Ruminal fluid was sampled at these same times and also at 2300 h. Duodenal digesta was sampled over 2 d to determine the site of herbage digestibility. Treatments did not affect daily herbage DMI (16.5 g/ kg of BW, SE = 0.0025; P > 0.05). However, they altered the eating pattern; the evening grazing bout of AHA and AHAF was greater (P < 0.05) and more intense (P < 0.05 for bite mass and rate, eating step, and intake rates). Ruminal nonglucogenic:glucogenic VFA ratio and pH were lower (P < 0.05) for AHA and AHAF during the evening. The flow of OM, N, microbial protein, and nonmicrobial OM to the duodenum did not vary (P > 0.05) among MHA, MHAF, and AHAF; however, it averaged 970, 40, 300, and 540 g/d, respectively, greater (P < 0.05) for AHA. Total tract digestibility did not differ (P > 0.05) for MHA, AHA, and AHAF, but was lower for MHAF (P < 0.05). Apparent ruminal digestion did not differ (P > 0.05) within fasted and nonfasted treatments; however, it was greater (P < 0.05) for fasted than nonfasted treatments. True OM ruminally digested did not differ (P > 0.05) among MHA, MHAF, and AHAF, but was greater (P < 0.05) for AHA. The results demonstrate the strong link between ingestion and digestion patterns, and its impact on nutrient supply. At the same amount of resource allocation, nutrient supply to grazing cattle can be modified through strategic grazing management.
本研究旨在评估牧草分配时间和禁食对采食行为模式、牧草摄入量、瘤胃发酵、十二指肠养分流量以及消化部位和程度的影响。处理方式包括下午（15:00，AHA）、上午（08:00，MHA）每日分配牧草，禁食20小时后的AHA（AHAF）以及禁食20小时后的MHA（MHAF）。四头安装了瘤胃和十二指肠瘘管的小母牛（体重279±99千克）采用拉丁方设计单独进行条带放牧于小麦牧场。每2分钟记录一次采食、反刍和空闲行为，在小母牛放牧期间（MHA和AHA为11小时；MHAF和AHAF为4小时）每小时测量一次咬食和采食步频。每天4次（08:00、12:00、15:00和19:00）测量瘤胃干物质池，以估算每日牧草干物质摄入量及其模式。在相同时间以及23:00采集瘤胃液。在2天内采集十二指肠消化物样本以确定牧草消化部位。处理方式对每日牧草干物质摄入量没有影响（16.5克/千克体重，标准误=0.0025；P>0.05）。然而，它们改变了采食模式；AHA和AHAF的傍晚放牧时段更长（P<0.05）且更强烈（咬食量和速率、采食步频和采食率P<0.05）。傍晚时，AHA和AHAF的瘤胃非生糖型挥发性脂肪酸与生糖型挥发性脂肪酸比例以及pH较低（P<0.05）。MHA、MHAF和AHAF之间十二指肠中有机物质、氮、微生物蛋白和非微生物有机物质的流量没有差异（P>0.05）；然而，AHA的平均流量分别高出970、40、300和540克/天（P<0.05）。MHA、AHA和AHAF的全消化道消化率没有差异（P>0.05），但MHAF较低（P<0.05）。在禁食和非禁食处理组内，表观瘤胃消化没有差异（P>0.05）；然而，禁食处理组比非禁食处理组更高（P<0.05）。MHA、MHAF和AHAF之间瘤胃中真正消化的有机物质没有差异（P>0.05）,但AHA更高（P<0.05）。结果表明采食和消化模式之间存在紧密联系，及其对养分供应的影响。在资源分配量相同的情况下，通过战略性放牧管理可以改变放牧牛的养分供应。
