Effect of heating on canola meal protein degradation in the rumen and digestion in the lower gastrointestinal tract of steers

Abstract

Commercially available canola meal (CM) was moist heat treated at 127 °C with steam-pressure of 117 kPa for 15, 30, 45, 60 and 90 min. The effect of moist heat treatment of CM on rumen degradability and lower gastrointestinal (GI) tract digestibility of rumen escape dry matter (DM) and nitrogen (N) was determined using three rumen and two duodenal cannulated steers. Rumen degradability was estimated by incubating sample-filled small nylon bags in the rumen of steers for 10 and 16 h. Lower GI tract digestibility was estimated using a sequence of ruminal in situ incubation, in vitro incubation in an acid-pepsin solution and a mobile nylon bag technique. DM and N degradation of treated CM were significantly (P < 0.01) reduced in the rumen while the digestibility of DM and N in the lower GI tract was increased at all treatment times. At 16 h incubation, N disappearance declined in the rumen from 74.4 to 18.9% and increased in the lower GI tract from 16.2 to 64.2% for control and for CM heat treated for 45 min, respectively. Analysis of heat treated CM showed a significant reduction (P < 0.01) in the soluble N while the concentration of pepsin insoluble N, acid detergent insoluble N and neutral detergent insoluble N were increased as heating time increased. These increases in general were not associated with a decrease in N disappearance in the lower GI tract. Moist heat treatment was effective in increasing rumen escape of CM protein without adverse effect on protein digestibility in the lower GI tract. Key words: Canola meal, rumen degradability, post ruminal digestion, moist heat treatment, insoluble nitrogen