Insolubility of Proteins in Ruminant Feeds by Four Methods

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Abstract
Samples of 15 feeds were assayed for protein insolubility by four methods. The 15 feeds were oats, wheat middlings, malt sprouts, corn gluten feed, wheat bran, soybean meal, cottonseed meal, barley, dehydrated alfalfa meal, hominy feed, corn, corn distillers dried grains, brewers dried grains, dried beet pulp and corn gluten meal. Ten samples of each feed, except for 101 samples of soybean meal and 119 samples of dehydrated alfalfa meal, were assayed. The four insolubility methods were: 1) boiling water for 1 hr and for 6 hr at 39 C in 2) one-tenth concentration of Burroughs' solution, 3) .15 M sodium chloride and 4) autoclaved rumen fluid. The mean insolubilities for feeds across all methods ranged from 49% of total nitrogen for corn gluten feed to 94% for dried beet pulp. The mean insolubilities for analytical methods across all feeds ranged from 67% for autoclaved rumen fluid to 80% for Burroughs' solution. The interaction of feed by analytical method was highly significant, and the within-feed correlations between methods ranged from ×.83 to +.99. The significant interaction and variable within-feed correlations imply that these insolubility methods must vary in their usefulness for predicting the undegradability of protein in the rumen. On the basis of these data, autoclaved rumen fluid may be superior to the other methods tested, but its common use would require standardization of pH and time of solubilization. Large variation in protein insolubility is present within feeds as well as among feeds. This large variation within feeds may be used along with the variation among feeds for formulating diets. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science