Evaluation of Nitrogen Solubility and the Dacron Bag Technique as Methods for Estimating Protein Degradation in the Rumen

Abstract

Nitrogen solubility after 1 h extraction in 10% mineral buffer and N disappearance from Dacron bags placed in the rumen of a fistulated cow were evaluated as methods for predicting protein degradation in the rumen. In vivo measures of ruminal protein degradation in cattle and sheep fitted with duodenal cannulae were available for 34 diets, thus enabling direct comparisons between protein solubility, in situ methods and in vivo measurements of protein degradation. Dacron polyester bags used in this study had an average pore size of 52 µm and were removed from the rumen at intervals of 1, 4, 8, 12, 17 and 24 h. Nitrogen disappearance at each interval of rumen exposure was correlated with N solubility. The correlation coefficient at 1 h of rumen exposure for all diets was .79 and decreased as exposure time increased. Correlations between N disappearance at 1, 4, 8, 12, 17 and 24 h of rumen exposure and in vivo measurements of ruminal protein degradation were −.08, .16, .29, .56, .55 and .68, respectively. The correlation coefficient between N solubility and in vivo protein degradation was .26. Several methods for using the Dacron bag technique to predict protein degradation were also investigated.