Production, composition, and oxidative stability of milk highly enriched in polyunsaturated fatty acids from dairy cows fed alfalfa protein concentrate or supplemental vitamin E

Given its elevated content of carotenoids, alfalfa protein concentrates (APC) have the potential to prevent oxidation of milk enriched in polyunsaturated fatty acids. The effects of feeding APC or supplemental vitamin E on production, composition, and oxidative stability of milk enriched in polyunsaturated fatty acids were evaluated using 6 lactating Holstein cows (224 ± 18 d in milk) in a replicated 3 × 3 Latin square (21-d periods, 14 d for adaptation). Treatment diets contained (dry matter basis) (1) 9% soybean meal (control, CTL); (2) 9% soybean meal + 300 IU of vitamin E/kg (VitE treatment); or (3) 9% APC (APC treatment). Cows received a continuous abomasal infusion of 450 g/d of linseed oil. As a result, milk fat content of cis-9,cis-12 18:2 increased from 1.08 ± 0.13 to 3.9 ± 0.40% (mean ± SD), whereas cis-9,cis-12,cis-15 18:3 increased from 0.40 ± 0.04 to 14.27 ± 1.81% during the experimental period compared with the pretrial period. Milk yield tended to be higher for APC (14.7 kg/d) compared with CTL (13.4kg/d), and was greater than that for VitE (13.0kg/d). Protein yield was higher in cows fed APC (518 g/d) compared with VitE (445 g/d) but was not different from that in cows fed CTL (483 g/d). These effects resulted in improved milk N efficiency in cows fed APC (26.1% of N intake secreted in milk) compared with CTL (23.0%) and VitE (22.9%). Feeding APC increased milk fat content of lutein (252 μg/g) compared with CTL (204 μg/g) and VitE (190 μg/g). Milk fat content of vitamin E was higher for APC (34.5 μg/g) compared with CTL (19.0 μg/g) and tended to be lower than that with VitE (44.9 μg/g). Redox potential of fresh milk from cows fed APC (152mV) was similar to that of VitE (144mV), but lower than that of CTL (189 mV). Treatments had no effect on fresh milk contents of dissolved oxygen (8.1 ± 1.5 mg/L), and conjugated diene hydroperoxides (2.7 ± 0.5 mmol/L). The concentrations of volatile lipid oxidation products (propanal, hexanal, hept-cis-4-enal, 1-octen-3-one) tended to be decreased by APC relative to CTL, whereas similar values were observed for VitE, except for hexanal, which was reduced by 40% in VitE. In conclusion, feeding APC to lactating dairy cows could serve as a source of dietary protein that improves dietary N utilization efficiency, and also as a preharvest technology to increase natural antioxidant levels in milk to limit oxidation.