Evaluation of Laboratory Techniques for Predicting Ruminal Protein Degradation

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Abstract
Five methods of measuring protein solubility, an in situ method and an in vitro method for measuring protein degradability were evaluated to determine which procedure most accurately predicted quantity of feed protein escaping ruminal fermentation. Feeds evaluated were soybean meal, blood meal, meat meal, corn gluten meal, distillers dried grains, brewers dried grains, distillers grains plus solubles, dehydrated alfalfa and soybean meal treated with sodium bentonite. Solubility was measured in 0.15 M NaCl, 10% Burroughs solution, 0.02 N NaOH, hot water and bicarbonate-phosphate buffer. In situ procedure was the incubation of feeds in dacron bags suspended in the rumen of cattle. In vitro procedure was incubation of feeds with 5 proteolytic enzymes. Results from these methods were correlated with protein degradability determined in vivo or calculated from growth trials. Protein solubility in hot water, 10% Burroughs solution and bicarbonate-phosphate buffer was closely correlated with in vivo protein degradability, 0.86, 0.69 and 0.87, respectively. Highest correlation for dacron bag incubations with in vivo degradability were at 12 and 24 h, 0.88 and 0.84, respectively. All proteolytic enzymes yielded highly significant correlations with protein degradability with incubations of 1 and 4 h and offered procedural advantages over the dacron bag technique.