Russell James B, Muck Richard E, Weimer Paul J
Plant, Soil and Nutrition Laboratory, Agricultural Research Service, USDA, Robert C. Holley Research Center, Ithaca, NY 14853, USA.
FEMS Microbiol Ecol. 2009 Feb;67(2):183-97. doi: 10.1111/j.1574-6941.2008.00633.x.
Ruminant animals digest cellulose via a symbiotic relationship with ruminal microorganisms. Because feedstuffs only remain in the rumen for a short time, the rate of cellulose digestion must be very rapid. This speed is facilitated by rumination, a process that returns food to the mouth to be rechewed. By decreasing particle size, the cellulose surface area can be increased by up to 10(6)-fold. The amount of cellulose digested is then a function of two competing rates, namely the digestion rate (K(d)) and the rate of passage of solids from the rumen (K(p)). Estimation of bacterial growth on cellulose is complicated by several factors: (1) energy must be expended for maintenance and growth of the cells, (2) only adherent cells are capable of degrading cellulose and (3) adherent cells can provide nonadherent cells with cellodextrins. Additionally, when ruminants are fed large amounts of cereal grain along with fiber, ruminal pH can decrease to a point where cellulolytic bacteria no longer grow. A dynamic model based on STELLA software is presented. This model evaluates all of the major aspects of ruminal cellulose degradation: (1) ingestion, digestion and passage of feed particles, (2) maintenance and growth of cellulolytic bacteria and (3) pH effects.
反刍动物通过与瘤胃微生物的共生关系来消化纤维素。由于饲料在瘤胃中停留的时间较短，纤维素的消化速度必须非常快。反刍过程有助于提高这种速度，反刍是一个将食物返回口腔再次咀嚼的过程。通过减小颗粒尺寸，纤维素的表面积可增加高达10^6倍。然后，消化的纤维素量是两个竞争速率的函数，即消化速率（K(d)）和固体从瘤胃中排出的速率（K(p)）。纤维素上细菌生长的估计因几个因素而变得复杂：（1）细胞的维持和生长必须消耗能量，（2）只有附着的细胞能够降解纤维素，（3）附着的细胞可以为非附着细胞提供纤维二糖。此外，当给反刍动物喂食大量谷物和纤维时，瘤胃pH值可能会下降到纤维素分解菌不再生长的程度。本文提出了一个基于STELLA软件的动态模型。该模型评估瘤胃纤维素降解的所有主要方面：（1）饲料颗粒的摄入、消化和排出，（2）纤维素分解菌的维持和生长，（3）pH值的影响。
