Over-toasting dehulled rapeseed meal and soybean meal, but not sunflower seed meal, increases prececal nitrogen and amino acid digesta flows in broilers

Abstract

Poorly digestible proteins may lead to increased protein fermentation in the ceca of broilers and hence, the production of potentially harmful metabolites. To evaluate effects of protein fermentation on gut health, an experimental contrast in ileal nitrogen (N) and amino acid (AA) flow is required. Therefore, our objective was to develop a model that creates a contrast in protein fermentation by increasing the prececal flow of protein within ingredients. To this end, we used additional toasting of protein sources and evaluated the effect on prececal N and AA flows. One-day-old Ross 308 male broilers (n = 480) were divided over 6 dietary treatments, with 8 replicate pens with 10 broilers each. Diets contained 20% of a regular soybean meal (SBM), high protein sunflower seed meal (SFM) or a dehulled rapeseed meal (dRSM) as is, or heat damaged by secondary toasting at 136°C for 20 min (tSBM, tSFM, or tdRSM). Ileal and total tract digesta flows of N and AA were determined with 5 birds per pen in their third week of life using an inert marker (TiO2) in the feed. Additional toasting increased the feed conversion ratio (FCR) only in birds fed dRSM (1.39 vs. 1.31), but not SBM and SFM (interaction P = 0.047). In SBM, additional toasting increased the flow of histidine, lysine, and aspartate through the distal ileum and excreted, while in SFM it had no effect on flows of N and AA. Toasting dRSM increased the prececal flows and excretion of N (862 vs 665 and 999 vs 761 mg/d, respectively) and of the AA. Of the ingredients tested, toasting dRSM is a suitable model to increase protein flows into the hind-gut, permitting the assessment of effects of protein fermentation.