Replacing palm fatty acid distillate by black soldier fly oil in the diet of dairy ewes: effects on animal performance, ruminal fermentation, plasma metabolites and oxidative stress

The current global scenario of animal feeding is characterized by limited land resources, increasing feed-food-fuel competition and growing concern about its contribution to environmental pollution. Feeding dairy animals with locally produced alternative feeds, as insect-derived fats, could partially alleviate this competition and contribute to a more sustainable production system. Nevertheless, to date, there are no in vivo studies evaluating the use of insect fats as feed in dairy sheep. Therefore, this study was designed to assess the effects of replacing palm fatty acid distillate, a conventional energy source, with black soldier fly (Hermetia illucens) oil in the diet of dairy ewes, with a focus on animal performance, ruminal fermentation, blood parameters and oxidative status. To this aim, 14 lactating Assaf ewes were included in a 2 × 2 change-over trial with 2 periods of 25 d each and 2 diets obtained by supplementing a TMR with either 2% DM of palm fatty acid distillate (PFAD diet) or 2% DM of black soldier fly oil (BSFO diet). Individual feed intake and milk yield were recorded 6 and 5 times per week, respectively, and individual milk samples were collected 3 times per week to analyze milk composition. At the end of each experimental period, blood samples were taken to assess blood metabolites, enzymes and oxidative status, and ruminal fluid was collected to measure pH, ammonia, and VFA. Additionally, on d 25 of each period ruminal fluid samples were also used as inoculum for 20-h in vitro batch cultures of ruminal microorganisms to examine gas and methane production and DM disappearance. Results indicated similar animal performance (i.e., BW, milk yield and milk composition, and feed efficiency metrics) and ruminal fermentation parameters between PFAD- and BSFO-fed ewes. The only exception was observed for in vitro methane production, which was higher in BSFO than in PFAD diet. Regarding blood metabolites and enzymes, replacing PFAD with BSFO only caused a tendency toward higher blood glucose and cholesterol levels, while oxidative status results showed a decrease in serum antioxidant capacity in BSFO ewes. Overall, replacing 2% DM PFAD with BSFO in the diet of lactating sheep resulted in similar animal performance and most ruminal fermentation parameters. However, its effects on in vitro methane production, certain blood metabolites (i.e., glucose and cholesterol), and oxidative status require further research.