PSIX-9 - Effect of calcium nitrate fed to dairy cows on nitrate residues, fatty acids profile, and antioxidant capacity in milk

Abstract: Six lactating cows (106.3 ± 14.8 DIM; 550.7 ± 21.8 kg BW) were enrolled in a replicated 3 × 3 Latin square to evaluate the supplementation of double salt of calcium ammonium nitrate decahydrate (CAN), composed by 16.5% N, 76.5% of nitrate (NO₃^-), and 85.0% DM, on NO₃^- and nitrite (NO₂^-) residues, fatty acids (FA) proportion, and antioxidant capacity in milk. Each period lasted 21 d, with 14 d for adaptation and 7 d for sampling. Treatments were URE (11.9 g/DM of urea as a control), CAN15: 15 g of CAN (11.5 g of NO₃^- on DM), and CAN30: 30 g of CAN (23 g of NO₃^- on DM). Milk samples were collected on d 15–16 of each period, frozen at –20°C, and after analyzed for NO₃^- and NO₂^- residues, fatty acids, and antioxidant capacity. Data were analyzed using PROC MIXED of SAS. Supplemental CAN increased by 26% NO₃^- residue in milk (P = 0.02), whereas did not affect (P < 0.05) NO₂^- concentration (average of 0.042 mg/L). Total CLA and short-chain FA were not affected (P > 0.05) by CAN. Medium-chain FA decreased linearly (P < 0.05), while long-chain FA (P = 0.06) and monounsaturated FA (P = 0.08) tended to increase linearly. Saturated FA reduced (P < 0.05) linearly; however, the total of polyunsaturated FA was not affected (P > 0.05). There were no effects of CAN (P > 0.05) on n-3, n-6, and n-6/n-3 ratio. Milk reducing power and TBARS concentration were not affected (P > 0.05) by CAN, whereas conjugated dienes increased (P = 0.02) linearly (URE= 47.6 vs. CAN15= 52.7 vs. CAN30= 63.4 mmol/kg of fat). Supplementing CAN at 30 g/DM reduced total saturated FA and increased conjugated dienes, caused possibly by lower rumen biohydrogenation, which might increase lipid oxidation in milk.