Comparing dehulled hemp meal and canola meal as a protein supplement for lactating dairy cows

Abstract

Effects of replacing canola meal with dehulled hemp meal in the diet of lactating dairy cows on the dry matter intake (DMI), milk production, milk fatty acid profile, blood metabolites, total-tract nutrient digestibility, and transfer of cannabinoids were determined in 12 lactating, nonpregnant Holstein cows. These cows were used in a 3 × 3 Latin square design with three 3-wk experimental periods consisting of 2 wk of adaptation and 1 wk of sampling. Cows received basal partial mixed rations supplemented with either 15% dry matter (DM) canola meal (CM15), 15% DM dehulled hemp meal (HM15), or 7.5% DM dehulled hemp meal and 7.5% DM canola meal (CM7.5HM7.5). Diets were formulated to be isoenergetic and isonitrogenous, but the HM15 and CM7.5HM7.5 diets contained, on average 1.2 percentage units more crude protein (CP) that the CM15 diet. The CP of the dehulled hemp meal contained less soluble protein than that of canola meal. Hence, the intake of soluble protein did not differ among diets. Canola meal contained less crude fat than hemp seed meal (3.46% vs. 8.25% DM). The lipid fraction of canola meal fat contained more oleic acid (C18:1 cis-9; 47.3 vs. 14.9 g/100 g of fatty acids, FA) and vaccenic acid (18:1 cis-11; 13.7 vs. 1.2 g/100 g of FA) and less linoleic acid (C18:2n-6; 21.9 vs. 55.7 g/100 g of FA) and α linolenic acid (C18:3n-3; 3.2 vs. 8.9 g/100 g of FA) than the lipid fraction of hemp seed meal. The hemp seed meal contained 4.9 µg/g cannabidiol, 5.1 µg/g cannabidiolic acid, and 0.1 µg/g tertahydroxycannabinolic acid A. Treatments did not differ in DMI, yields of milk, milk protein and milk fat, total-tract neutral detergent fiber digestibility, and blood plasma concentrations of β-hydroxybutyrate and nonesterified FA. Apparent total-tract DM digestibility was lowest in the HM15 treatment, whereas the CP digestibility and the concentrations of urea in blood, urine, and milk were lowest in the CM15 treatment. Cannabinoids were not detected in urine, milk, and blood plasma. Replacing canola meal with hemp seed meal increased milk fat contents of polyunsaturated fatty acids (PUFA), which were 3.42, 3.90, and 4.25 g/100 g of FA for the CM15, CM7.5HM7.5, and HM15 treatments, respectively. Especially, the milk fat contents of 18:2n-6 (1.99 vs. 1.56 g/100 g FA) and 18:3n-3 (0.31 vs. 0.43 g/100 g FA) were increased by hemp meal feeding. Especially, the milk fat contents of 18:2n-6 (1.99 vs. 1.56 g/100 g FA) and 18:3n-3 (0.31 vs. 0.43 g/100 g FA) were increased by hemp meal feeding. Our data show that hemp seed meal is a suitable and safe replacement for canola meal as a feed for lactating dairy cows and that this replacement increases CP digestibility and urea in urine, milk, and blood plasma, as well the PUFA content of milk fat.

Keywords: cannabinoids; cows; hemp meal; milk production; protein.