Comparison of linseed oil and its ethyl esters as fat supplements in milk replacer: Impacts on physical properties, nutrient digestibility, health, and oxidative status of dairy calves.

The study aimed to examine the physical properties of milk replacer (MR) supplemented with linseed oil or ethyl esters of polyunsaturated fatty acids of linseed oil, and the subsequent impacts on nutrient and fatty acid (FA) digestibility, growth performance, health status, and some immune response and oxidative stress parameters in pre-weaned dairy calves. Eighteen Holstein calves were assigned to one of 3 treatments: a control MR with no supplemental fat added (CON), MR supplemented with 30 mL/d of linseed oil (LO), or MR supplemented with 30 mL/d of ethyl esters of polyunsaturated fatty acids of linseed oil (EELO). Physical properties of MR, including creaming index (CI), droplet size distribution, and microstructure, were evaluated after mixing/homogenizing with water. Apparent total-tract digestibility of nutrients was determined by fecal collection during 2 periods (22-25 and 50-53 d of age). Digestibility was calculated for dry matter, organic matter, crude protein, crude fat, and individual fatty acids (C16:0, C18:0, C18:1, C18:2, and C18:3). Titanium dioxide (TiO2) was included in the diet as an indigestible marker. Health parameters were recorded daily from 12 to 53 d of age, and some immune and oxidative stress indicators were measured in blood samples collected on 12, 25, 43, and 53 d of age. Performance parameters such as MR and starter mixture intake, total DMI, ADG, feed efficiency as well as nutrient intakes, nutrient digestibility coefficients, immune status, or oxidative stress parameters were analyzed as repeated measures using a linear model and the GLIMMIX procedure in SAS. Supplementation of MR with LO or EELO affected CI and droplet size characteristics, with EELO showing improved MR stability compared with LO, including a lower CI, more favorable droplet size distribution, and reduced fat globule coalescence. Fat supplementation did not affect DMI. However, final BW, ADG, and feed efficiency tended to be greater in calves receiving EEPUFALO. Digestibility of OM and CP was greater in the EELO group in both periods, whereas LO supplementation reduced C18:2 digestibility during the first experimental period. Digestibility of selected FA, including C16:0 and C18:3, was higher in calves supplemented with EELO. Irrespective of treatment, older calves exhibited greater digestibility of crude fat and PUFA, indicating an age-related improvement in lipid digestion. Fat supplementation reduced the number of days with diarrhea and the number of treatment days, with the most pronounced effects observed in the EELO group. Supplementation with EELO was associated with reduced concentrations of measured inflammatory markers, particularly TNF-α, and a tendency toward lower serum haptoglobin. In addition, EELO supplementation improved oxidative status, reflected by reduced total oxidant status, increased total antioxidant status, and a reduced oxidative stress index. In conclusion, EELO exhibited superior physical, nutritional, and biological effects compared with LO, demonstrating that the chemical form of FA is a critical factor influencing their digestibility, bioavailability, and health-promoting effects in pre-weaned dairy calves.