Feeding Live or Dried Black Soldier Fly Larvae (Hermetia illucens) to laying hens – Effects on Immune Traits, Egg Quality, Feather Condition, Body and Organ Weights

Abstract: Due to increasing prices and potential scarcity of soybean meal (SBM), there is growing demand for alternative and sustainable protein sources in poultry production. Black soldier fly larvae (BSFL) have proven to be a suitable alternative based on nutritional value and sustainable production. Feeding live larvae to laying hens can stimulate natural foraging behaviour and improve animal welfare, but requires careful management to standardize nutrient composition of the larvae. Dried larvae, on the other hand, have a longer shelf life and are easier to handle. Various studies have analysed the effects of live BSFL and BSFL meal feeding in laying hens, but there is a gap regarding the effects of dried whole larvae feeding, and there is a scarcity of literature regarding the impact of BSFL feeding on immune parameters. This study aims to evaluate the effect of live and dried black soldier fly larvae feeding to laying hens. For this purpose, 360 Bovans Robust White hens were randomly allocated at 18 weeks of age to three diet groups: control, live larvae, and dried larvae. The control group received a standard soybean meal based diet, while the live and dried larvae groups received 20% replacement of daily dry matter intake as live or dried larvae, respectively, along with a balanced pelleted feed. Data was collected from 30 to 50 weeks of age. Immune parameters recorded were white blood cell counts and specific antibody responses to infectious bronchitis virus (IBV) booster vaccination. The white blood cell populations enumerated were heterophils, monocytes, lymphocytes, thrombocytes, and some subpopulations of lymphocytes, including MHC II+ lymphocytes (B cells), CD4+CD25- (T helper cells), CD4+CD25+ (activated helper and/or regulatory T cells), and CD4-CD25+ (non-CD4 activated T cells). In addition, the expression levels of MHC II and chicken mannose receptor MRC1L-B on monocytes was measured. Internal and external parameters of egg quality and feather condition score were evaluated. At the end of the experiment, hen body weight and gastrointestinal tract (GIT) organs were weighed. The control group diet was unintentionally manufactured with low sodium content, which is known to cause reduced body weight, cannibalism, and feather pecking. This makes it difficult to interpret the results. Nonetheless, comparisons between dried and live larvae are still relevant. Hens in both larvae groups had darker yolk colour with age (p<0.0001) and higher yolk weight (p=0.05). The feather condition of the control group on the neck, back, cloaca, and tail was poorer than both larvae groups, and control hens had more rear body skin injuries (p<0.0001). The control group hens were significantly lighter in weight than the larvae group hens (p=0.005). However, there was no significant difference between the treatments in organ weights (i.e. proventriculus, liver, gizzard, and fat pad). Additionally, there were no significant differences between groups in leukocyte counts, expression of surface markers, and antibody response to IBV vaccination. Abstract Moreover, egg quality parameters, such as egg weight, eggshell breaking strength, eggshell thickness, eggshell weight, and albumen thickness, were similar in all groups (p>0.05). The findings of this study are in agreement with previous research on BSFL meal feeding, demonstrating no difference in leukocyte counts and antibody responses to IBV vaccination, suggesting that the form of larvae feeding may not have an impact on the immune response. The results indicate that the low sodium diet of the control group had an impact on the integument condition and body weight. Egg quality and organ weight were also unaffected with treatment, indicating that substituting 20% of daily dry matter intake with live or dried larvae can serve as a sustainable alternative feed ingredient. Dried larvae, with their consistent nutritive value and easy management, appear to be the more practical option. Further research is needed to validate the findings with a proper control group.