Effect of increasing doses of abomasally infused linseed oil on animal performance and oxidative stability of milk in Holstein dairy cows

Abstract Text:

To evaluate the effect of increasing doses of post-ruminal supply of linseed oil (LO), as a source of polyunsaturated fatty acids (PUFA), on animal performance and oxidative stability of milk, five Holstein dairy cows (36 ± 2 DIM, 38.7 ± 4.7 kg milk/d; Mean ± SD) were randomly distributed in a 5×5 Latin square design (14-d periods; 11 d of adaptation). All cows were fed the same ration and LO was abomasally infused continuously at 0, 75, 150, 300, and 600 g/d using peristaltic pumps. Oxidation measurements were done on fresh non-homogenized milk and on homogenized milk stored at 4°C during 11 d under fluorescent light. Data were analyzed using a mixed model including the random effects of period and cow, and the fixed effects of treatment, time and their interaction in the repeated measures analyses. A peroxidability index (PI) was calculated as: 0.025×Monoenoates + 1×Dienoates + 2×Trienoates + 4×Tetraenoates + 6×Pentaenoates + 8×Hexaenoates, to account for individual oxidation sensitivity of FA. Dry matter intake and yield of energy corrected milk decreased linearly with increasing dose of LO (P<0.05). Milk fat concentration decreased quadratically (P<0.05) reaching a nadir at 300 g of LO/d, whereas the yields of fat and protein decreased linearly (P<0.05). The concentration and yield of lactose were not different among treatments. The concentration of PUFA increased linearly with LO dose (P<0.001). Accordingly, the PI of fresh milk increased linearly with dose from 2.0 mg/g milk in the control, to 10.8 mg/g milk at the highest dose (P<0.001). Conjugated diene hydroperoxides in fresh milk increased linearly with dose (P<0.001), whereas conjugated triene hydroperoxides and redox potential were not affected. Volatile lipid oxidation products such as propanal, hexanal, trans-2-hexenal/hex-cis-3-enal, and hept-cis-4-enal increased linearly with dose (P<0.001), whereas 1-octen-3-one was not affected, and trans-2, cis-6-nonadienal and trans-2, trans-4-nonadienal were not detected in fresh milk. During storage, similar increasing trends were observed across treatments for propanal, hexanal, trans-2-hexenal/hex-cis-3-enal, hept-cis-4-enal, and trans-2, cis-6-nonadienal in homogenized milk (time P<0.001). Treatment by time interactions were detected for 1-octen-3-one and trans-2, trans-4-nonadienal. In conclusion, increasing doses of abomasally infused LO negatively affected animal performance. Despite small differences among individual oxidation products, overall, a linear increase in milk PUFA led to a quadratic response in total identified volatile compounds which tended to reach a plateau at 300 g of LO/d.

Keywords: dairy cows, n-3 fatty acids, oxidation