The effect of supplemental bioactive fatty acids on growth performance and immune function of milk-fed Holstein dairy calves during heat stress.

This study aimed to evaluate the effects of different supplemental fat sources [soybean oil (SBO) as a source of n-6 fatty acid and fish oil (FO) as a source of n-3 fatty acids] in the starter feed of milk-fed dairy calves during the hot season. Forty Holstein calves (3 d of age; 39.67 kg of body weight; ten calves per group) were randomly assigned to the experimental treatments as follows: (1) starter feed supplemented with no fat source (CON), (2) starter feed supplemented with 3% SBO (DM basis), (3) starter feed supplemented with 3% FO (DM basis), and (4) starter feed supplemented with an equal mixture of SBO and FO (1.5% each, DM basis). The milk feeding schedule was constant for treatments and all calves were weaned on d 65 of age. Results show that calves had greater starter intake, average daily gain, and body length when fed SBO compared to other treatments. However, feed efficiency was increased and inflammatory indicators (tumor necrosis factor-alpha, serum amyloid A and haptoglobin) concentrations were reduced in the calves fed FO compared to the other treatments. In summary, it was revealed that SBO rich in n-6 FA improved starter intake and growth performance, while FO rich in n-3 FA could improve the immune function of calves. Due to the current experimental condition, an equal mixture of SBO and FO (1.5% each, DM basis) can be recommended to have an optimum growth performance and immune function while the calves are reared under the heat conditions.