Regulation of serum reproductive hormones, gap junction proteins, and cytokine profiles in laying hens fed varying levels of expanded black soldier fly meal

This study examined the impact of expanded black soldier fly (EP-BSF) meal on laying hens' reproductive hormones, gap junction proteins, cytokines, and performance. Over the 12 weeks trail period, 400 Hy-Line brown hens procured at 24 weeks of age underwent a completely randomized design with 5 treatments, 8 replicates, and 10 birds per replicate. The hens received a control diet (CON) or diets with 3 %, 6 %, 9 %, or 12 % EP-BSF. Results demonstrated that lower EP-BSF levels showed a linearly higher (p < 0.05) hen day egg production (HDEP) from 30 to 33 weeks and a linearly higher (p < 0.05) egg mass (EM) in the cumulative weeks comparable to CON. Tendencies towards a linearly higher average egg weight (AEW) was observed when EP-BSF was incorporated at lower levels comparable to CON during 34-37 weeks (p = 0.079), as well as in the cumulative weeks (p = 0.056). Yolk color was quadratically higher (p < 0.024) during 30-33 weeks, with higher tendency (p = 0.050) in the cumulative weeks as the EP-BSF level increases. Albumin weight was linearly higher (p < 0.05) at lower EP-BSF supplementation level comparable to CON at 26-29 weeks and at the cumulative weeks, with linearly higher tendency (p = 0.062) at 34-37 weeks. Eggshell thickness was quadratically increased (p < 0.05) at 30-33 weeks, with a quadratically higher tendency (p = 0.050) during the cumulative weeks as the level of EP-BSF increased. Serum estradiol (E2) levels were linearly increased (p < 0.05) in the lower EP-BSF groups, correlating with increased expression of connexins GJA1 and GJA4 in oviductal tissues and lower tumor necrosis factor-alpha (TNF-α). In conclusion, the incorporation of lower levels of EP-BSF had similar HDEP, AEW, EM, and albumin weight as CON. We attributed this to the increased E2 levels resulting in lower TNF-α, and higher expression of GJA and GJA4 in the chicken oviduct. Our findings also strongly indicate estrogen plays a role in modulating the expression of connexins. These findings suggest that lower EP-BSF in layer diet may serve as an alternative protein source for poultry feed.