In vitro ruminal fermentation kinetics of diets with crambe cake protein replacing soybean meal protein by gas production technique

The objective of this study was to evaluate ingredients and diets containing increasing levels of crambe cake protein replacing soybean meal protein, with in vitro ruminal fermentation parameters using a gas production technique. Diets were formulated for feedlot lambs and contained different levels of crambe cake protein (0, 250, 500, 750, and 1000 g kg-1) replacing soybean meal protein. Corn silage was used as roughage. Carbohydrate digestion rates were estimated using the in vitro gas production technique and the cumulative gas production kinetics were analyzed using the bicompartmental logistic model. The parameters values of ruminal degradation kinetics were generated using the R statistical program with the Gauss-Newton algorithm and then subjected to analysis of variance and regression (when necessary) according to a completely randomized experimental design with five treatments and five replications. Upon carbohydrate fractionation of ingredients and experimental diets, it was observed that corn grain and corn silage presented the highest levels of total carbohydrates (TC), with values of 128.3 and 464.8 g kg-1 dry matter (DM) in fraction B2, respectively. Lower TC content was found for soybean meal and crambe cake (CC). There was a predominance of fractions A + B1 in the ingredients and experimental diets. The B2 fraction decreased in the diets with the inclusion of the CC protein, and CC presented the highest C fraction. Protein fractionation (g kg-1 DM and g kg-1 crude protein - CP), the ingredients and diets showed a higher proportion of fractions A and B1 + B2. In in vitro degradation, the diet without CC (0 g kg-1 DM) showed the highest final cumulative gas production (365.04 mL g-1 of incubated DM), while the CC presented the lowest volume (166.68 mL g-1 of incubated DM). The gas volume of non-fibrous carbohydrate fermentation and fibrous carbohydrate degradation rate exhibited a quadratic effect according increasing levels of CC (Pmax = 265.8 g kg-1 DM and Pmin = 376.3 g kg-1 DM, respectively). The lag time and final gas volume showed a decreasing linear effect with increasing levels of CC protein. The degradation rate of non-fibrous carbohydrates and the final volume of fibrous carbohydrates did not differ. Replacing soybean meal protein with CC protein at the level of 250 g kg-1 of dry matter in diets formulated for feedlot lambs leads to good profiles of ruminal fermentation kinetics with respect to the degradation of fibrous and non-fibrous carbohydrates.