Performance and health status of preweaning dairy calves fed milk replacer supplemented with increasing doses of ethyl esters of polyunsaturated fatty acids of linseed oil

This study aimed to determine the effect of supplementing milk replacer (MR) with increasing doses of a mixture of ethyl esters of polyunsaturated fatty acid of linseed oil (EEPUFALO; α-linolenic acid 55.5%, linoleic acid 13.3%, and oleic acid 18.0%) on growth performance, health, immune status, and oxidative stress parameters of preweaning dairy calves. A total of 54 Holstein-Friesian calves (5 d of age, 39.8 ± 0.69 kg, both males and females) were divided into 3 groups, each consisting of 18 animals: a control group and 2 treatment groups (D1 and D2), receiving 0, 15, and 30 mL/d of EEPUFALO incorporated into the MR, respectively. Each calf remained in the experiment from 5 to 56 d of age and had free access to starter mixture. Feed intake and fecal fluidity were monitored daily, body weight and body morphometric measurements were recorded weekly, and blood samples for hematological, immune status and oxidative stress parameters were collected on 14, 28, 42, and 56 d of age. Supplementation with increasing doses of EEPUFALO quadratically increased average daily MR and total DMI, with the highest in D2. Supplementation with EEPUFALO increased final BW and total BW gain in a quadratic manner, with the highest performance in group D2. Average daily gain and feed efficiency also followed a quadratic response, with the highest values in group D2. Supplementation with EEPUFALO had limited effects on hematological parameters, though it significantly reduced neutrophil percentage and increased lymphocyte concentration, particularly in the D2 group. We further found that EEPUFALO tended to lower serum haptoglobin levels and significantly decreased tumor necrosis factor-α concentrations, with linear response indicating the most pronounced effects in group D2. Although total oxidant status showed a numerical decrease, total antioxidant status increased significantly, especially in group D2, contributing to a tendency for reduced oxidative stress index. No significant changes were observed in serum superoxide dismutase activity and plasma malondialdehyde concentration. Supplementation with EEPUFALO improved calf health, as indicated by fewer days of veterinary care. In conclusion, supplementation of MR with EEPUFALO at a dose of 30 mL/d improved calf performance, potentially due to its beneficial effects on immune function and the reduction of oxidative stress.