Hoover W H, Stokes S R
Division of Animal and Veterinary Sciences, West Virginia University, Morgantown 26506.
J Dairy Sci. 1991 Oct;74(10):3630-44. doi: 10.3168/jds.S0022-0302(91)78553-6.
Establishing conditions under which rumen fermentation will be optimized requires an understanding of the nutrient requirements of the mixed microbial population. The major nutrients required by rumen microbes are carbohydrates and proteins, but the most suitable sources and quantities needed to support maximum growth have not been determined. Digestion of proteins results in the production of peptides, which can accumulate in the rumen. Peptides are further hydrolyzed to amino acids, some of which are deaminated, producing ammonia. Although peptides, amino acids, and ammonia all may individually serve as sources of N for various microbes, the total population achieves the highest growth rate on mixtures of all three sources. In a somewhat analogous manner, carbohydrates are digested by exoenzymes to oligosaccharides that are available for crossfeeding by the mixed microbial population. Based on data from both in vitro and in vivo studies, there is general agreement that rate of digestion of carbohydrates is the major factor controlling the energy available for microbial growth; in addition, rate of digestion of total carbohydrate is directly related to proportion of starches, pectins, and sugars. Proteins affect both total fermentation and production of microbial DM per unit of carbohydrate fermented. It appears that the quantity of ruminally available protein needed to optimize microbial growth may, under some conditions, be as high as 14 to 15% of diet DM.
要确定瘤胃发酵最优化的条件，需要了解混合微生物群体的营养需求。瘤胃微生物所需的主要营养物质是碳水化合物和蛋白质，但支持最大生长所需的最合适来源和数量尚未确定。蛋白质消化会产生肽，肽会在瘤胃中积累。肽会进一步水解为氨基酸，其中一些会脱氨，产生氨。虽然肽、氨基酸和氨都可以单独作为各种微生物的氮源，但所有三种来源的混合物能使整个微生物群体达到最高生长速率。以类似的方式，碳水化合物会被外切酶消化为寡糖，可供混合微生物群体交叉利用。根据体外和体内研究的数据，人们普遍认为碳水化合物的消化速率是控制微生物生长可用能量的主要因素；此外，总碳水化合物的消化速率与淀粉、果胶和糖的比例直接相关。蛋白质会影响总发酵以及每单位发酵碳水化合物产生的微生物干物质。在某些条件下，优化微生物生长所需的瘤胃可利用蛋白质的量可能高达日粮干物质的14%至15%。
