Incorporation of two levels of black soldier fly (Hermetia illucens L.) larvae fat or extruded linseed in diets of growing rabbits: effects on growth performance and diet digestibility

The use of black soldier fly (BSF) (Hermetia illucens L.) larvae fat as a lipid supplement in growing rabbit's diet was evaluated at two levels of supplementation in comparison to two levels of extruded linseed. Forty-eight weaned rabbits aged 35 days were individually housed in digestibility cages and randomly allocated to one of the four diets: Linseed-Low (30 g/kg of fat from linseed), Linseed-High (60 g/kg of fat from linseed), BSF-Low (30 g/kg of BSF fat), BSF-High (60 g/kg of BSF fat). Animals had ad libitum access to water and feed during 5 weeks, and were slaughtered at 70 days of age. In the fourth week of the trial, faeces were collected to allow the evaluation of total tract apparent digestibility (TTAD) of the diets. Mortality, dry matter (DM) intake, average daily gain, slaughter live weight, and carcass, liver, perirenal fat, scapular fat, and digestive tract weights were not affected (P > 0.05) either by fat source or fat level. The TTAD of DM, organic matter, ether extract, and gross energy were lower (P < 0.05) in the diet containing BSF fat than in linseed diets, and the decrease observed ranged between 2.3 to 3.1 percent points. With increasing the fat inclusion level, ether extract TTAD increased (P < 0.001) but the cellulose TTAD decreased (P < 0.01). Overall, diets containing BSF fat resulted in a slightly lower TTAD than linseed diets, but this seemed not to have affected growth performance and carcass yield. In conclusion, BSF fat could be considered an alternative lipid source for growing rabbit diets highlighting similar productive results to linseed.