Effect of dietary sunflower oil and feeding frequency on milk conjugated linoleic acids in early lactating Holstein cows

Feeding diets supplemented with vegetable oil is known to increase milk fat concentration of different isomers of conjugated linoleic acids, but a great variability has been observed between cows. The objective of the present study was to evaluate whether the feeding behavior can explain part of this individual variation. Eight multiparous Holstein cows were used in a replicated 4 × 4 Latin square design with 3-week periods. Treatments were: (1) the control basal diet fed in one meal; (2) the control basal diet fed in 12 meals; (3) the basal diet + 5% sunflower oil ( S-oil ) fed in one meal; (4) the basal diet + 5% S-oil fed in 12 meals. Cows receiving their ration once a day consumed 3.6 meals/d of the control diet, and 5.2 meals/d of the S-oil diet, whereas cows fed 12 times daily consumed 10.3 meals/d of both control and S-oil diets (oil × meal, P = 0.03). The total numbers of chews per day and per gram of DM (eating + ruminating) as well as total rumination time per day and per kilogram of DM were greater for cows fed S-oil ( P < 0.05). Increasing feeding frequency to 12 meals reduced the fluctuations in time of rumen pH, NH 3 -N, and volatile fatty acids (time × meal, P < 0.01). Dietary addition of S-oil did not affect ruminal pH but decreased the concentration of acetate. Increasing feeding frequency from 1 to 12 meals/d had no effect on feed consumption, but S-oil reduced DMI. Actual milk yield was similar between treatments. Milk fat concentration and yield were decreased when S-oil was fed in the diet once a day, but this negative impact was not observed with 12 meals/d (oil × meal, P = 0.03). Feeding S-oil did not affect milk fat concentration of cis -9, cis -12 18:2, but increased trans -10 18:1, trans -11 18:1, trans -10, cis -12 18:2, and cis -9, trans -11 18:2. Feeding frequency had minor impacts on milk fatty acids. A great variability has been observed between cows regarding milk fat concentrations of cis -9, trans -11 18:2 (0.79 to 2.24 g/100 g fat) and trans -10, cis -12 18:2 (0.03 to 0.15 g/100 g fat) in response to S-oil. Increasing meal frequency was effective in preventing milk fat depression that occurred when S-oil was added to the ration. However, we were unable to link the variations in milk cis -9, trans -11 18:2 and trans -10, cis -12 18:2 levels to changes in the cow’s feeding behavior.