Effects of replacing soybean meal with canola meal or treated canola meal on ruminal digestion, and omasal nutrient flow in lactating dairy cows

Abstract Text: Treated canola meal (TCM) was produced as an attempt to increase the RUP fraction of canola meal (CM) with the goal of increasing AA availability for absorption in the small intestine. The objective of this study was to measure nutrient and microbial omasal flow when CM and TCM replaced soybean meal (SBM) in the diet of dairy cows. Six rumen-cannulated cows were blocked into 2 blocks of 3 cows and randomly assigned within blocks to 3 dietary sequences in a replicated, 3x3 Latin square design with 21 days of adaptation and 7 days of sampling. Treatments differed only in CP source, which were: SBM, CM, or TCM. The TCM was treated by extrusion, with added molasses to promote the browning reaction. All diets contained (DM basis) 30% alfalfa silage, 30% corn silage, 4% soy hulls, 2.4% mineral-vitamin premix and 16% CP. The SBM diet contained 25% high moisture corn (HMC) and 8.6% SBM; the canola diets contained 22% HMC and 11.4% CM or TCM. Omasal sampling was performed during the last week of each period. Data were analyzed using the MIXED procedure of SAS. Orthogonal contrasts were used to compare effects of different protein sources (SBM vs. CM + TCM) and (CM vs. TCM). Partial data are presented in Table 1. Compared to SBM, CM and TCM increased N intake (P = 0.04) and there was a trend (P = 0.10) to increase RDP supply (kg/d), and N truly digested in the rumen (kg/d). There were no differences in DMI, ruminal digestibility, efficiency of ruminal microbial synthesis, and flows of: RUP, non-microbial-non-ammonia-N, and total microbial-non-ammonia-N among diets. Results indicate that both canola diets may increase N intake and RDP supply. Treating CM by extrusion did not affect microbial N flow at the omasal canal. Under the conditions of the present study, treating CM by extrusion was not effective in increasing RUP flow in dairy cows.

Keywords: nitrogen metabolism, rumen undegraded protein, omasal flow