Comparison of Traditional Canola, Low-Poly Canola, and Rapeseed Meals as Modifiers of Bovine Milk Fatty Acid Profile.

Developing a canola/rapeseed-based biodiesel industry in the U.S. will generate large quantities of seed meal. To date, most canola meal in the U.S. has very little oil remaining after crushing followed by solvent oil removal. However, in smaller crush plants, solvent extraction would be neither economic nor practical, and hence seed meals from these smaller crush facilities would likely have considerably higher oil content. Bovine milk fatty acid (FA) profile can be modified through manipulation of dietary FA composition, thus making milk and dairy products healthier for human consumption. Residual oil in canola and rapeseed meals is relatively rich in monounsaturated FA (60-70%) and low in polyunsaturated FA (20-30%) and is an excellent source of lipid in dairy cattle diets. Therefore, the objective of this experiment was to investigate the potential of mechanically extracted traditional canola meal, low-polyunsaturated canola meal, and rapeseed meal to alter bovine milk FA profile. The experiment was a replicated 4 × 4 Latin square design trial with 8 lactating dairy cows (643 ± 21.9 kg body weight and 109 ± 15.1 days in milk at the beginning of the trial) and 4 experimental periods. Six of the cows were ruminally cannulated. Each experimental period was 17 d in duration, 12 d for adaptation to the diets and 5 d for sampling. Treatments were: (1) traditional, solvent extracted canola meal (CONTROL); (2) traditional, mechanically extracted canola meal (CANOLA); (3) mechanically extracted low-polyunsaturated canola meal (LOWPOLY); and (4) mechanically extracted low-glucosinolate rapeseed meal (RAPESEED). All meals were supplemented at 3.75 kg/d per cow (approximately 12 to 13% of dietary DM) during the entire experiment. The meals were top-dressed and mixed with a portion of the basal diet. Crude protein (CP) and fat concentrations (% of DM) of the meals were: 43.0 and 3.1%, 32.8 and 16.1%, 45.2 and 13.7%, and 34.3 and 17.9% for CONTROL, CANOLA, LOWPOLY, and RAPESEED, respectively. Major FA in the meals were (g/100 g FA): CANOLA – 18:1, 60.0%, 18:2, 20.3%; LOWPOLY – 18:1, 76.1%, 18:2, 10.1%; and RAPESEED – 18:1, 16.7%, 18:2, 12.8%, and 22:1, 42.0%. The control canola meal was not analyzed; its FA composition was assumed to be similar to that of the mechanically extracted canola meal (CANOLA) and the amount of fat in control meal was negligible. The diets were fed at 5% orts and contained (% of DM): corn silage, 44.3 to 44.8%; alfalfa haylage, 8.3 to 8.4%; grass hay/straw mix, 4.4%, ground corn grain, 11.1 to 11.2%; bakery by-product, 6.6 to 6.7%; expeller soybean meal (SoyChoice, Wenger's Feed Mill Inc., Rheems, PA), 6.3 to 6.4%; cottonseed hulls, 3%; canola/rapeseed meal, 12 to 13%; and mineral/vitamin premix, 3%. The diets had the following composition (DM basis; CP, neutral-detergent fiber, and ether extract): 16.0, 31.1, and 3.9%; 14.9, 31.3, and 5.5%; 16.6, 31.0, and 5.2%; and 15.1, 32.1, and 5.7% for CONTROL, CANOLA, LOWPOLY, and RAPESEED, respectively. Based on NRC (2001) and actual DM intake (DMI) and milk yield and composition, all diets provided net energy of lactation in excess of requirements and the CONTROL and LOWPOLY diets provided metabolizable protein in excess of requirements. The CANOLA and RAPESEED diets were marginally deficient in metabolizable protein (by about 1.0 and 1.2%, respectively). All data were analyzed using the MIXED procedure of SAS (SAS Inst., Inc., Cary, NC) with cow as the random effect. Milk yield, DMI, and some rumen fermentation parameters were analyzed as repeated measures assuming an autoregressive(1) covariance structure. All experimental meals (CANOLA, LOWPOLY, and RAPESEED) reduced DMI compared with the CONTROL: 29.3, 28.9, 28.2, and 30.9 kg/d, respectively (SEM = 0.56; P < 0.01). Milk yield was also greater (SEM = 1.93; P = 0.052) for the CONTROL compared with the other treatments: 47.1, 44.9, 46.7, and 45.0 kg/d, CONTROL, CANOLA, LOWPOLY (a trend at P = 0.07), and RAPESEED, respectively. Feed efficiency (milk yield ÷ DMI) was similar (1.52 to 1.62 kg/kg; P = 0.12) among treatments. Milk fat content was unusually low in this trial (2.80 to 2.94%) and indicative of milk fat depression, but was unaffected by treatment (SEM = 0.20; P = 0.54). Fat (3.5%)-corrected milk yield was reduced (P = 0.025) by CANOLA compared with the other treatments. Concentration of milk true protein was also unaffected by treatment (2.93 to 3.00%; SEM = 0.05; P = 0.32). Milk fat and protein yields were similar (P = 0.24 and P = 0.19, respectively) among treatments. Rumen pH was slightly lower (P = 0.041) for CONTROL and RAPESEED vs. CANOLA and LOWPOLY (6.25 and 6.25 vs. 6.34 and 6.36, respectively). Ruminal ammonia concentration was not affected (P = 0.41) by treatment. Concentration of acetate in ruminal fluid was lower (P = 0.006) for all experimental meals compared with the CONTROL (average of 68.0 vs. 74.7 mM, respectively). Treatment had no effect on ruminal concentrations of propionate, butyrate, and total volatile fatty acids (P = 0.58, 0.39, and 0.27, respectively). The CONTROL diet resulted in higher (P = 0.003) acetate:propionate ratio than the experimental meals. Milk fat from CONTROL cows contained greater (P = 0.001) concentrations of 14:0 (10.5 vs. 9.1 g/100 g total FA) and 16:0 (P < 0.001; 24.9 vs. 23.4, 21.0, and 22.9 g/100 g FA, CONTROL, CANOLA, LOWPOLY, and RAPESEED, respectively). RAPESEED had lower (P < 0.05) 16:0 compared with CANOLA and LOWPOLY. Concentration of 18:0 was higher (12.5 vs. 11.6 g/100 g FA; P = 0.009) for CANOLA compared with the other treatments. Concentration of cis 18:1 was increased (P = 0.024) by the experimental meals compared with the CONTROL (24.7, 25.4, and 24.9 vs. 22.6 g/100 g FA for CANOLA, LOWPOLY, RAPESEED, and CONTROL, respectively). Total conjugated linoleic acid (CLA) content was increased (P = 0.001) by LOWPOLY compared with the other treatments (1.17 vs. and average of 0.83 g/100 g FA, respectively). Concentration of cis-9, trans-11 CLA was greater (P = 0.003) for LOWPOLY compared with the other treatments (907 vs. 613 mg/100 g FA, respectively). RAPESEED increased (2.33 g/100 g FA; P < 0.001) cis-13 22:1 compared with the other treatments. The sum of saturated FA in milk fat was greater (P = 0.004) for the CONTROL compared with the experimental meals (61.2 vs. 56.4 g/100 g FA). Concentration of monounsaturated FA was increased (P = 0.002) by the experimental meals compared with the CONTROL (33.3 g/100 g FA) and was greater for RAPESEED compared with CANOLA (40.0 vs. 36.8 g/100 g FA, respectively). The sum of trans FA was increased (P = 0.025) by CANOLA and LOWPOLY vs. CONTROL (9.83, 9.97, and 8.10 g/100 g FA, respectively). In conclusion, canola and rapeseed meals with higher fat content were unpalatable and reduced DMI of high-producing dairy cows, which resulted in reduced milk yield, but had no effect on milk fat and protein concentrations. Due to the higher total fat content of the experimental diets, ruminal acetate concentration was reduced compared with the control, solvent-extracted canola meal. The experimental meals had a profound effect on milk fatty acid profile, reducing concentration of total saturated and increasing the sum of monounsaturated and trans fatty acids.