Evaluation of canola meal as a protein supplement for dairy cows: A review and a meta-analysis

Abstract

Huhtanen, P., Hetta, M. and Swensson, C. 2011. Evaluation of canola meal as a protein supplement for dairy cows: A review and a meta-analysis. Can. J. Anim. Sci. 91: 529–543. A review and a meta-analysis were conducted to compare the feeding value of soybean meal (SBM) and canola meal (CM) in dairy cows and to evaluate the effects of heat-treatment of CM (TCM) on the performance of dairy cows. The dataset included in total 292 treatment means from 122 studies, in which dietary crude protein (CP) concentration was increased by replacing energy supplements with protein supplements. A mixed model regression analysis with random study effect was used to estimate the marginal production responses to different protein sources. The differences between the slopes were compared by t-test. All protein sources increased dry matter intake, but the responses were greater (P<0.01) for CM and TCM compared with SBM. Feeding CM or TCM produced greater (P<0.01) daily milk yield responses than SBM (3.4±0.19 and 3.7±0.25 vs. 2.1±0.25) kg kg−1increase in CP intake. Marginal milk protein yield responses (g kg−1increase in CP intake) were greater (P<0.01) for CM (136±5.4) and TCM (133±8.5) compared with SBM (98±8.0). Smaller response to incremental CP intake can partly be related to the higher average dietary CP concentration in SBM studies. Literature data on rumen ammonia N concentration and omasal protein flow did not support the higher ruminal tabulated ruminal CP degradability of CM compared with SBM. It is concluded that CM can successfully be substituted for SBM on isonitrogenous basis and that most feed evaluation systems overestimate metabolizable protein concentration of SBM relative to CM.