Replacement of soybean meal with canola improves short-term milk yield and nitrogen-use efficiency in high-producing, early-lactation Holstein cows.

Soybean meal is globally probably the most favoured protein supplement in dairy cow diets, but increased demand has elevated its price, which necessitates evaluating other options. One such option is canola meal, with limited research suggesting that canola meal is used as efficient or more efficiently for milk production than soybean meal. Some research showed that the inclusion of canola meal increased DMI, milk yield and milk protein compared to soybean meal and other protein sources. Interpretation suggests an increased supply of histidine and increased absorption of essential amino acids, particularly methionine and lysine. Being rather poor in lysine, but having more methionine than soybean meal which on the other hand is rich in lysine, one suspects that a combination of canola and soybean meal should actually be ideal. This principle is what resulted in the experiment of the authors cited.

Twelve lactating Holstein cows (four first lactation and eight multi-lactation cows, 36 ± 8 days in milk) were used in a 3 x 3 Latin square design with three treatments and four replicates over three 21-day periods. The cows were fed diets formulated with respectively no canola meal (Control: CM-0), 50% (CM-50), or 100% canola meal (CM-100), with canola meal replacing soybean meal. The experimental diets were formulated to be iso-nitrogenous and iso-energetic. Several parameters were measured.

The main results showed that DMI (23.2 kg per day average), milk composition, energy-corrected milk yield (ECM) (34.5 kg per day average), total VFA, and blood metabolites were not affected by treatment. However, cows fed canola meal diets produced an average of 2.9 kg per day (not ECM) more milk that control cows (only soybean meal). The apparent nitrogen efficiency was greatest in the cows fed CM-50. Compared to control, crude protein digestibility and ruminal ammonia concentration were higher and lower for cows fed CM-50 or CM-100, respectively.

The results showed that substituting soybean meal with canola meal in the diet had positive effects on milk production, nitrogen-use efficiency, and increased total tract digestibility. The main advantage is when 50% soybean meal was replaced with canola meal, rendering substance to previous explanations that the combination apparently optimizes essential amino acid absorption, in particular histidine, methionine and lysine.