Miyaji M, Ueda K, Hata H, Kondo S
Graduate School of Agriculture, Hokkaido University, Sapporo, Hokkaido, 060-8589, Japan.
J Anim Sci. 2014 Apr;92(4):1574-81. doi: 10.2527/jas.2013-6676. Epub 2014 Mar 18.
Eight Thoroughbred horses were used to examine the effects of grass hay intake on the fiber digestion and the retention time of digesta in the total gastrointestinal tract and the hindgut segments. The horses were randomly assigned to 2 groups and offered 2.0 (high intake [HI]) or 1.3 kg DM/(100 kg BW • d; low intake [LI]) of timothy hay in equal amounts every 3 h for 17 d. The digestibility and total tract mean retention time of digesta (tMRT) in the total gastrointestinal tract were measured from d 11 to d 15. To measure the mean retention time of digesta in each hindgut segment (sMRT), the horses were euthanized on d 17, after being fed a series of hay markers that were labeled with different rare earth elements. The digesta were collected from the ileum, cecum, right ventral colon (RVC), left ventral colon (LVC), left dorsal colon, right dorsal colon (RDC), and small colon (SC) to measure fiber digestibility, sMRT, VFA concentration, and fibrolytic activities. The digestibility of NDF and ADF in the total gastrointestinal tract was lower (P < 0.01) for HI than for LI. The cumulative disappearance of NDF and ADF from the ileum to the LVC attained 90% of total tract digestion regardless of hay intake. Values did not differ according to treatments in the ileum and the cecum but were lower (P < 0.01) for HI than for LI in the postcecal segments. This was caused by the smaller increase in the cumulative NDF and ADF disappearance from the cecum to the RVC for HI than for LI. The solid phase tMRT was shorter (P = 0.04) for HI than for LI. Although sMRT in the RDC and SC were shorter (P = 0.04 and P < 0.01, respectively) for HI than for LI, no differences were observed in the other hindgut segments. There was no difference between treatments in the total VFA concentration, VFA proportions, or the specific activity of carboxymethyl cellulase and xylanase in each hindgut segment. The fibrolytic activity for the cecum and RVC were greatest and decreased beyond the LVC. A clear relation between mean retention time and fiber digestion was observed in the total gastrointestinal tract, but the segments where a difference in sMRT was detected because of the intake were not the same as those with the fiber digestibility depression. Although the reduction in total tract fiber digestibility with increased feed intake was clearly shown to occur between the cecum and RVC, which were the main segments for fiber digestion, it could be explained neither by the sMRT nor by the fibrolytic activity in these segments.
选用8匹纯种马，研究禾本科干草采食量对纤维消化以及总胃肠道和后肠段食糜停留时间的影响。将马匹随机分为2组，每3小时等量投喂2.0（高采食量[HI]）或1.3 kg干物质/（100 kg体重•天；低采食量[LI]）的猫尾草属干草，持续17天。在第11天至第15天测量总胃肠道中食糜的消化率和总消化道平均停留时间（tMRT）。为了测量每个后肠段食糜的平均停留时间（sMRT），在第17天给马匹投喂一系列用不同稀土元素标记的干草标记物后，对其实施安乐死。从回肠、盲肠、右腹结肠（RVC）、左腹结肠（LVC）、左背结肠、右背结肠（RDC）和小结肠（SC）收集食糜，以测量纤维消化率、sMRT、挥发性脂肪酸（VFA）浓度和纤维分解活性。高采食量组总胃肠道中中性洗涤纤维（NDF）和酸性洗涤纤维（ADF）的消化率低于低采食量组（P < 0.01）。无论干草采食量如何，从回肠到左腹结肠NDF和ADF的累积消失量达到总消化道消化量的90%。回肠和盲肠中的数值在不同处理间无差异，但在盲肠后段，高采食量组低于低采食量组（P < 0.01）。这是由于高采食量组从盲肠到右腹结肠NDF和ADF累积消失量的增加幅度小于低采食量组。高采食量组的固相tMRT短于低采食量组（P = 0.04）。虽然高采食量组右背结肠和小结肠的sMRT短于低采食量组（分别为P = 0.04和P < 0.01），但在其他后肠段未观察到差异。各处理间总VFA浓度、VFA比例或每个后肠段中羧甲基纤维素酶和木聚糖酶的比活性无差异。盲肠和右腹结肠的纤维分解活性最高，在左腹结肠之后降低。在总胃肠道中观察到平均停留时间与纤维消化之间存在明显关系，但因采食量而检测到sMRT差异的肠段与纤维消化率降低的肠段不同。尽管随着采食量增加总消化道纤维消化率的降低明显发生在盲肠和右腹结肠之间，这两个部位是纤维消化的主要部位，但这既不能用这些部位的sMRT来解释，也不能用纤维分解活性来解释。
