Rumen undegradable protein in feedstuffs: Impact of dilution rate on nitrogen compounds outflow in a semi-continuous culture fermenter (RUSITEC).

This study evaluated the impact of increasing the dilution rate on the outflow of nitrogen (N) compounds in a semi-continuous culture fermenter (RUSITEC). Five semi-continuous culture fermenters were used to test three dilution rates of the liquid phase (3, 5, and 7 %/h) in an incomplete 3 × 3 Latin square design. Three 10-day assays were performed, each consisting of a 5-day adaptation and stabilization period followed by 5 days of sampling. Each fermenter received 10 g of a total mixed ration, and artificial saliva was continuously infused, at the different experimental rates. The liquid effluent was measured and sampled daily for further analysis. Increasing the dilution rate did not affect N degradability or ammonia-N outflow, but linearly increased the outflow of small peptides and decreased the outflow of amino acids (p < 0.05). The sum of free amino acids and small peptides flowing out of the fermenter represented 21 to 54% of the N that disappeared from bags. The outflow of small peptides from fermentation vessels was directly impacted by increased dilution rate of the incubation medium, indicating that they may contribute significantly to the rumen undegradable protein fraction of feedstuffs.