Ruminal Fermentation

Abstract

Equipped with a complex and advanced digestive tract that cultures diverse anaerobic microbes, adult ruminant animals possess a unique ability to not only harvest feed and forage but also to employ microbes to degrade complex fiber sources and produce nutrients essential for and readily digested by the host animal. When fermented, fiber, starches, and sugars yield volatile fatty acids, carbon dioxide, and methane. Protein sources are partially degraded to ammonia, volatile fatty acids and gases. Lipids are partly cleaved to glycerol and fatty acids with unsaturated fatty acids being hydrogenated. Most organic compounds in the diet can be fermented by anaerobic microbes within the rumen. The extent to which feed components are degraded is limited either by the accessibility of various feed components to ruminal microbes, by the enzymatic activity of ruminal microbes (that will vary with ruminal conditions), or the duration of time available for fermentation. Based on the ratios of volatile fatty acids produced and fermentation balance equations, energetic efficiency of fermentation and yield of various gases (carbon dioxide and methane) and ATP can be calculated. From ATP yield, the yield of microbial organic matter and microbial protein can be estimated. Ruminal fermentation occasionally becomes dysfunctional resulting in bloat, acidosis, and specific toxicoses. Chemical and antimicrobial compounds included in the diet can alter the microbial population or the fermentation process to avoid metabolic disorders and enhance energetic efficiency. Extent of ruminal digestion and yield of microbial products can be quantified most reliably by using live animals equipped with surgically installed cannulas for sampling digesta. But to simplify and speed feed quality measurement and to test effects of various feed additives, analytical laboratories incubate samples with ruminal microbes using batch and continuous culture techniques or suspend feeds within Dacron bags in the rumen for various durations of time. Thanks to their ability to both harvest and digest complex carbohydrates prevalent in diverse locations and present in agricultural and industrial wastes, ruminants throughout the world serve mankind through converting useless and underutilized resources into food and fiber products that have high nutritional and economic value.