Dietary effects of black soldier fly oil, soybean oil, and tallow on performance, egg traits, hormones, and oviductal connexins in laying hens

The increasing demand for sustainable and energy-dense feed in poultry nutrition has prompted the exploration of alternative dietary fat sources. The objective of this study was to evaluate how three fat sources including black soldier fly oil ( BSFO ), soybean oil ( SBO ), and tallow ( TA ) with circular economy relevance differed in their effects on laying hens’ performance, egg and eggshell quality, reproductive hormones, inflammatory markers, and oviductal connexin expression. A 12-week trial was conducted with 288 Hy-Line Brown layers aged 24 weeks allocated to 6 treatments, 6 replicates, and 8 birds per replicate in a completely randomized design. The trial was categorized into 3 phases (26-29 weeks, 30-33 weeks, and 34-37 weeks) subjected to six dietary treatments as diet+2% BSFO ( BSF2 ), diet+4% BSFO ( BSF4 ), diet+2% SBO ( SOY2 ), diet+4% SBO ( SOY4 ), diet+2% TA ( TA2 ), and diet+4% TA ( TA4 ). Fat source significantly influenced laying performance, egg quality, inflammatory status, and gene expression, whereas inclusion level and interaction showed no significant effect. Overall, the findings show that hens fed the SBO treatments had higher (p=0.015, p=0.009) hen-day egg production during 30-33 weeks, and 34-37 weeks comparable to BSFO treatments and TA2, which outperformed TA4. Egg mass was higher (p=0.030) in the SBO treatments comparable to BSFO during 34-37 weeks. The Haugh unit was higher (p=0.016) in the BSFO treatments which was comparable to SBO during 26-29 weeks. Eggshell thickness was higher (p=0.043) in the BSFO treatments comparable to SBO treatments and TA4 during 26-29 weeks. Eggshell hardness was higher (p=0.045, p=0.023) in BSFO and SBO treatments during 26-29 weeks, and 34-37 weeks. Moreover, SBO and BSFO treatments significantly reduced serum tumour necrosis factor-alpha levels and increased the expression of gap junction protein alpha 1/connexin 43 ( GJA1) and gap junction protein alpha 4/ connexin 39 ( GJA4 ) in the infundibulum. Conversely, TA inclusion was associated with higher pro-inflammatory response and lower connexin expression. The study concludes that BSFO, SBO, and TA, each with circular economy relevance, can support productive performance and physiological health in laying hens. While all three oils are viable energy sources, their biological impacts vary according to each fatty acid profile.