Submitted to: National Forage Testing Association Workshop Proceedings
Publication Type: Proceedings
Publication Acceptance Date: August 15, 1995
Publication Date: N/A
Interpretive Summary: Protein in most forage legumes, such as alfalfa, is rapidly degraded in the first compartment of the ruminant stomach. Unfortunately the amount of rapidly degraded carbohydrate is usually insufficient to match the available protein, resulting in excessive nitrogen loss through animal excretion. Matching rapid protein digestion with carbohydrate that is equally rapidly digested results in more efficient utilization of plant nitrogen by the animal. Within plants there are three pools of carbohydrate that fit this requirement; total soluble sugars, starch, and the pectic polysaccharides found in the cell wall. Measurement of these pools would provide an indication of the total rapidly available carbohydrate in a given feed. This paper briefly describes a convenient method of measuring all of these carbohydrate pools in a single sample.
Technical Abstract: Forages, such as alfalfa (Medicago sativa), are considered excellent nutrient sources for ruminants due to high levels of protein. However, rapid ruminal degradation of forage protein results in inefficient utilization. Improved utilization occurs if adequate supplies of rapidly fermented carbohydrate are available to capture the protein in new microbial biomass. Carbohydrate fractions within the plant that meet this requirement are cytoplasmic sugars, starch, and pectic polysaccharides. Pectic polysaccharides are a unique group of complex wall polysaccharides that are quickly fermented in the rumen with first order rate constants approaching 0.5 h-1. A simplified method for determining total pectic polysaccharides in legumes has been developed. This method is based upon a total hydrolysis of plant walls followed by neutral sugar and total uronosyl measurement. Combining this method with current methods for determining soluble nonstructural carbohydrates and starch allows accurate determination of the readily available energy in forage legumes.