Effect of soybean meal and canola meal extrusion and reducing the dietary level of crude protein on blood parameters and rumen microbial populations of feedlot calves

This study aimed to investigate the effect of reducing the dietary level of crude protein (CP) and inclusion of extruded soybean meal (SBM) and canola meal (CM) on blood and ruminal parameters, the population of methanogens, and hyper-ammonia producing bacteria (HAB) of feedlot calves. To this purpose, 36 male calves were used in a completely randomized experimental design with six treatments and six replicates. Experimental treatments included: 1) Control (CP=15%, SBM (15SBM)), 2) SBM (CP=13%, 13SBM), 3) Extruded SBM (CP=13%, EXSBM), 4) CM (CP=13%, 13CM), 5) Extruded CM (CP=13%, EXCM), and 6) Fish meal (CP=13%, FM). Concentrations of albumin, total protein, creatinine, and blood urea nitrogen in experimental treatments decreased compared to 15SBM (P>0.05). The highest values of ruminal ammonia and acetate and the lowest amounts of propionate and volatile fatty acids (VFA) were observed in the 15SBM (P<0.05). The minimum ruminal HAB population was observed in EXSBM and EXCM and then in 13SBM, 13CM and FM and was maximum in 15SBM (P<0.05). Also, treatments fed EXSBM and EXCM had a smaller methanogens population than the control group (P<0.05). Based on the results obtained, decreasing dietary CP level and processing of extrusion for SBM and CM decreased HAB population, rumen ammonium, and blood urea concentration. Furthermore, extrusion declined methanogens bacteria population and acetate to propionate ratio and increased total VFA concentrations which can be considered as an indication of the rumen improvement in fermentation efficiency index.