Hermetia illucens Oil in Calf Milk Replacers Sustains Nutrient Digestibility with Subtle Effects on Concentrate Intake Depending on the Inclusion Level

Background: This study evaluates whether different fat formulations of cow’s milk re-placers (CMRs) for calves, made by replacing palm and coconut oils with Hermetia il-lucens oil, affect the apparent digestibility of the diet and fecal nutrient excretion at weaning. The effects of these formulations on calf intake, growth, and feed efficiency were also assessed. Methods: Three commercial isoenergetic and isonitrogenous milk replacers, which differed only in the fat source, were tested over ten weeks: CMR C (80/20 palm/coconut oil), CMR T20 (80/20 palm/insect oil), and CMR T40 (60/40 palm/insect oil). Twenty-four calves were randomly assigned to three groups. Feces samples were collected individually at 65–69 days of age. Results: The feed efficiency and the apparent digestion of nutrients did not differ significantly among the groups. However, the T20 group tended to have a lower dry matter intake than the C group and lower average body weight than the T40 group. Conclusions: Black soldier fly oil did not impair apparent nutrient digestibility or feed efficiency at weaning. However, the T20 formulation was associated with reduced solid feed intake and lower average body weight compared with those for T40, indicating that formulation and optimal in-clusion level require further investigation.