December 19, 2013
US rapeseed meal, DDGs may become alternative to soymeal
Rapeseed meal or dried distiller grains with solubles (DDGS), by-products of ethanol production, may offer an economical alternative to soymeal in North American dairy rations.
These protein supplements can effectively replace soymeal and, in two recent meta-analyses, compared with soymeal, rapeseed meal had a positive effect on milk and milk protein yields.
The objective of this study was to determine if the positive responses observed with inclusion of rapeseedmeal 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 % crude protein) and isoenergetic (1.56Mcal/kg of net energy of lactation) diets formulated to slightly exceed nutrient requirements. Diets contained 38% grass hay and 62% corn-based concentrate including soymeal, rapeseed 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 1.14 kilogrammes/day, respectively. Lactose yield did not differ among diets although milk lactose content tended to be lower with rapeseed meal and WDDGS diets than with soymeal and HPDDG diets.
Lysine availability was affected by treatments: the highest whole-body irreversible loss rate (ILR) was observed for the rapeseed meal diet (371g/day) and the lowest for HPDDG diet (290g/day); values for soymeal 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 rapeseed meal diet, however, had numerically the highest His and Met ILR. Plasma concentrations of most of the essential AA were higher with the rapeseed 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 rapeseed meal (2,795g/day); the two diets with the lowest whole-body glucose rate of appearance (rapeseed 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 rapeseed meal in dairy rations could be linked to a greater supply of metabolisable protein, including some essential AA, especially His, Lys, and Met, as glucose availability was certainly not increased in cows fed the rapeseed meal diet.