Implementation of a metabolizable energy regression model for black soldier fly larvae fat in broiler chicken diets: effect on growth performance, nutrient digestibility, and selected physiological indices

This study aimed to evaluate the validity of estimated apparent metabolizable energy (AME) regression models for Hermetia illucens ( HI) larval fat in broiler chicken diets during various feeding periods. Additionally, it investigated the effects of HI larval fat on selected serum biochemical, immunological, and humoral indices. The experiment involved 300 7-day-old male Ross 308 chicks assigned to two dietary groups (15 replicate pens). The trial lasted 28 days and the following treatments were applied: a basal diet enriched with soybean oil (SO) or larval fat (HI) as the sole source of dietary fat energy, respectively. To obtain an equal energy value of both diets, the AME values for SO and HI were set as follow: 34.2 and 37.54 MJ/kg (7-14 days), 38.4 and 37.72 MJ/kg (15-28 days), and 37.1 and 37.70 MJ/kg (29-35 days), respectively. No differences in body weight gain, feed intake, or feed conversion ratio were observed between the treatments. However, increased coefficients of apparent ileal digestibility (CAID) of crude protein and apparent ileal digestible energy (AIDE), with elevated lipase activity, were recorded in the HI treatment. The inclusion of insect fat led to reduced serum immunoglobulin G and thyroxine (T4) concentrations. Moreover, the HI group showed a decreasing trend in aspartate aminotransferase, free T4, and interleukin 6 levels. In conclusion, the regression models for HI larval fat used in broiler diets proved to be effective. Additionally, insect fat demonstrated superiority over SO in promoting favourable CAID of crude protein and AIDE. Furthermore, HI may contribute to improved liver function and immune status of birds, as well as affect thyroid hormone metabolism.