Evaluation of Detergent Analysis in Estimating Nutritional Value of Browse

Abstract

The efficiency of carbohydrate and protein extraction from browse by detergent solutions was investigated. Standard and sequential acid-detergent extractions removed virtually all of the hemicellulose, total soluble sugars, water-soluble polysaccharides, and pectin. Sequential extraction of browse with neutral and acid detergents removed more of the protein than either neutral detergent or separate acid detergent, while quantitatively retaining the cellulose. Neutral detergent with sodium sulfite removed an average of 22% of the hemicellulose, and probably solubilized portions of the true lignin and cutin. Consequently, sodium sulfite should not be used in the neutral-detergent procedure, ND-AD sequential analyses should be used, and hemicellulose must be determined colorimetrically if a precise determination is necessary. J. WILDL. MANAGE. 45(4):937-947 Meaningful fractionation of soluble and structural portions of plant material is essential in determining the nutritional value of ingested foods. Since the deficiencies of the traditional proximate analysis of crude fiber and nitrogen-free extract have become well documented (Ely and Moore 1955, Williams and Bevenue 1956, Gaillard 1958, Van Soest 1967, Morrison 1976, Asp 1979), several schemes to replace proximate analysis have been proposed. Detergent analysis (Van Soest and Wine 1967) is generally superior to proximate analysis in terms of partitioning plant-cell constituents into meaningful nutritive entities while requiring a minimum of time and equipment. Although detergent analysis has been applied to a wide range of forages, modifications have been necessary when analyzing fodder samples (Arora 1977) and cereals (Baker 1977). The accuracy of detergent analysis procedures with woody plant parts has not been examined sufficiently. Browse differs from many forages in that it contains significant amounts of cutin (Robbins et al. 1975) and phenolic compounds (Feeny and Bostock 1968), which have complex chemistries resulting in greatly complicated extractability (McLeod 1974). Although tannins (phenolic polymers) are unimportant constituents in grasses and hays (Van Soest 1966), they may be potential obstructions to the detergent analysis scheme when applied to browse (Robbins et al. 1975). Phenolics vary in structure from a single aromatic ring to highly complex polymeric substances, such as tannins and lignin. All plant phenolics may potentially form insoluble complexes with protein and cellulose, although the various phenolic groups differ in reactivity, preferred substrates, and types and conditions of bonding (Wong 1973, McLeod 1974). Phenolics are even more problematic in that they are, by strict definition, cell solubles, yet bear little nutritional similarity to this otherwise highly digestible fraction. Tannins are known to precipitate dietary, enzymatic, and microbial protein, all of which contribute to depressed protein, dry-matter, and cell-soluble digestibilities (Wong 1973; McLeod 1974; Nelson et al. 1975; Mould and Robbins 1981, 1982). Phenolics that enter the lower gut may combine with the proteins of 1 Present address: Department of Biology, St. Mary's College, Notre Dame, IN 46556. J. Wildl. Manage. 45(4):1981 937 This content downloaded from 157.55.39.130 on Wed, 23 Nov 2016 04:40:51 UTC All use subject to http://about.jstor.org/terms 938 ESTIMATING NUTRITIONAL VALUE. Mould and Robbins the epithelial wall and reduce total nutrient-absorption capabilities (McLeod 1974). Simple phenolics and hydrolyzed portions of tannin polymers may be absorbed and produce massive hepatic and renal disorders (Arhelger et al. 1965, Boler et al. 1966, Camp et al. 1967, Texl and Koneeny 1968). Clearly, the potential action of phenolics upon digestive processes is not similar to either cell solubles or cell-wall fractions, and should therefore be partitioned as a separate, distinct entity. The purpose of this study was to evaluate the role and extraction efficiences of detergent analysis when used on browse. These data were then used to isolate potential interferences to the detergent analysis scheme and to develop appropriate modifications. Finally, a method for determining phenolic content in conjunction with detergent analysis was sought so that phenolics might be schematically separated from the cell-soluble and cell-wall fractions. We gratefully acknowledge support received from the Washington Department of Game, National Science Foundation (DEB 76-24329), and Washington State University. The laboratory assistance of D. K. Hulbert is appreciated. We are indebted to P. Van Soest for his valuable criticism of an earlier draft.