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 and metabolism during the transition from the preruminant to the ruminant stage. This study evaluated the effects of Hermetia illucens oil inclusion in CMRs on FA intake, fecal excretion, apparent digestibility, and hair cortisol concentra-tions 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. Overall fat intake, fecal fat excretion, and apparent fat digestibility did not differ among treatments. However, treatment affected fecal excretion and apparent digestibility of individual FAs. T20 calves showed lower fecal C15:0 excretion than T40 calves. Ap-parent digestibility of MUFA and LCFA was higher in T20 than in C, while total un-saturated FA and n-6 FA digestibility was higher in insect-oil groups than in controls. Hair cortisol concentrations did not differ among treatments. Partial replacement with H. illucens oil did not impair total fat utilization or hair cortisol concentrations but modified the fecal excretion and apparent digestibility of specific FAs.