Hermetia illucens Oil in Calf Milk Replacers: Effects on Fatty Acid Digestibility, Fecal Excretion, and Hair Cortisol at Weaning

The use of alternative lipid sources in calf milk replacers (CMRs) may influence fatty acid (FA) digestion during the transition from the pre-ruminant to the ruminant stage. This study evaluated the effects of Hermetia illucens oil inclusion in CMRs on dietary FA intake, fecal excretion, apparent digestibility, and hair cortisol concentrations in dairy calves. Twenty-four calves were randomly assigned to three isoenergetic and isonitrogenous CMRs (n = 8/group) differing in fat source: 80:20 palm/coconut oil (C), 80:20 palm/insect oil (T20), or 60:40 palm/insect oil (T40). Calves were gradually weaned at 70 days of age, and fecal samples were collected from days 65 to 69. Dietary fatty acid (FA) intake differed among treatments, reflecting variations in lipid composition and solid feed consumption. No statistically significant differences in hair cortisol concentrations were detected among dietary treatments (P = 0.128). Partial replacement with H. illucens oil did not affect overall apparent fat digestibility during the weaning period, under the experimental conditions and in the breed investigated. However, T20 showed higher apparent digestibility of long-chain fatty acids and monounsaturated fatty acids, while T20 and T40 showed higher n-6 FA digestibility than the control. These differences may primarily reflect variations in the fatty acid composition of the experimental diets.