Dietary phytogenic inclusion level affects production performance and expression of ovarian cytoprotective genes in laying hens

A 12-wk study was conducted to investigate the effects of a phytogenic premix (PP) inclusion level on production performance, and the expression of genes relevant for detoxification (aryl hydrocarbon receptor; AhR) and antioxidant capacity (Nuclear factor erythroid 2-related factor 2; Nrf2) in the ovaries of laying hens. The PP consisted of bioactive substances derived from ginger, lemon balm, oregano, and thyme substances (Anco FIT-Poultry). Depending on PP inclusion level (i.e., 0, 500, 750, 1,000, and 1,500 mg/kg diet) in the basal diet, 385 laying hens Hy-Line Brown, 20-wk-old were assigned into 5 treatments: CON, P500, P750, P1000, and P1500, with 7 replicates of 11 hens with ad libitum access to feed and water. Performance parameters were closely monitored on a weekly basis and analyzed in the following 3 experimental periods: 1 to 4 wk, 5 to 8 wk, and 9 to 12 wk of treatment administration (i.e., 21–24, 25–28, and 29–32 wk of layers age, respectively). At the end of the 8th and 12th wk of the experiment (i.e., 28 and 32 wk of layers age), a layer from each replicate was selected, euthanized, the ovaries sampled and stored deep frozen until gene expression analysis. Data were analyzed by ANOVA and means compared using Tukey's honest significant difference test. Polynomial contrasts tested the linear and quadratic effect of PP inclusion levels. Results revealed that PP inclusion, improved (P < 0.05) laying rate and egg mass, compared to CON. Increasing PP inclusion level enhanced laying rate and egg mass, linearly and quadratically and peaked at P1000 (P < 0.05). In the ovaries, the AhR pathway genes assessed were down-regulated (P < 0.05) mainly at P1000 and P750 treatments. In addition, PP related cytoprotective potential was demonstrated via beneficial changes seen for the majority of the Nrf2-pathway genes assessed with the P1000 displaying most significant differences from CON. Conclusively, new data highlighted beneficial cytoprotective effects of PP inclusion on layer ovaries and documented further layer performance, with the inclusion level of 1000 mg PP/kg diet being the most prominent.