Canola meal (CM) or by-products of ethanol production (dried distillers grain) may offer an economical alternative to soybean meal in North American dairy rations.
These protein supplements can effectively replace soybean meal and, in two recent meta-analyses, canola meal had a positive effect on milk and milk protein yields compared with soybean meal.
The objective of this study was to determine if the positive responses observed with inclusion of canola meal in dairy rations could be explained by an increased availability of His, Lys, Me, or glucose.
Eight Holstein dairy cows were used in a replicated 4×4 Latin square with 14-day periods. Cows were fed isonitrogenous (17.2 percent crude protein) and isoenergetic (1.56Mcal/kg of net energy of lactation) diets formulated to slightly exceed nutrient requirements. Diets contained 38 percent grass hay and 62 percent corn-based concentrate including soybean meal, canola meal, corn high-protein DDG (HPDDG), or wheat DDG plus solubles (WDDGS) as the single protein supplement. The effect of protein supplements on availability of His, Lys, Met and glucose was estimated using variations in the whole-body flux of these nutrients, determined by isotopic dilution.
As planned, dry matter intake and milk and milk protein yields were not affected by treatments and averaged 23.7, 31.4, and 1.14kg/day, respectively. Lactose yield did not differ among diets although milk lactose content tended to be lower with canola meal and WDDGS diets than with soybean meal and HPDDG diets.
Lysine availability was affected by treatments: the highest whole-body irreversible loss rate (ILR) was observed for the canola meal diet (371g/day) and the lowest for HPDDG diet (290g/day); values for soybean meal and WDDGS were intermediate (330 and 316g/day, respectively).
Availability of His and Met did not vary among diets and WB ILR averaged, respectively, 129 and 124g/day; the canola meal diet, however, had numerically the highest His and Met ILR. Plasma concentrations of most of the essential AA were higher with the canola meal diet and lower with the HPDDG diet, the exception being Leu for which the concentration was highest for the HPDDG diet. Glucose whole-body rate of appearance was altered by diet, with the highest mean observed for SBM (3,036g/day) and the lowest for canola meal (2,795g/day); the two diets with the lowest whole-body glucose rate of appearance (canola meal and WDDGS) also had the lowest dietary starch concentration.
Overall, this study suggested that positive responses in milk and milk protein yields observed with inclusion of canola meal in dairy rations could be linked to a greater supply of metabolizable protein, including some essential AA, especially His, Lys, and Met, as glucose availability was certainly not increased in cows fed the canola meal diet.
Source: Journal of Dairy Science