Effects of different levels of clove bud (Syzygium aromaticum) on performance, intestinal microbial colonization, jejunal morphology, and immunocompetence of laying hens fed different n-6 to n-3 ratios

The current study was carried out to assess the effects of different levels of clove bud (Syzygium aromaticum) powder on performance, intestinal microbial colonization, jejunal morphology, and immunocompetence of laying hens receiving diets with different ratios of n-6 to n-3. A total of 160 laying hens, 43 weeks of age, were assigned to 8 experimental diets with 5 cages of 4 birds each. Dietary treatments consisted of two ratios of n-6 to n-3 (16.71 and 2.35) and three levels of clove bud (0, 0.2 and 0.4%) in a 2×3 factorial arrangement alongside a group receiving a high vitamin E content (200 mg/kg) in each n-6 to n-3 ratio, as the positive control, fed during a 70-d feeding trial. The in vitro study indicated that clove essential oil exhibited more than 10-fold higher antioxidant activity to inhibit 2-2-diphenyl-1- picric hydrazyl (DPPH) free radical than vitamin E (P<0.05). Dietary inclusion of clove bud powder noticeably decreased (P<0.0001) the heterophile to lymphocyte ratio. A decline in n-6 to n-3 ratio and a rise in clove bud powder content increased the secondary antibody titer against sheep red blood cell (P<0.05; P<0.01) as well as Newcastle virus (P<0.01; P<0.001). Furthermore, supplementation of fish oil and clove bud powder, either alone (P<0.01; P<0.05) or combined (P<0.01; P<0.001), markedly decreased the ileal Escherichia coli and Salmonella enumerations. Feeding clove bud, especially the 2% level, led to increase in villus height (P<0.05), villus height to crypt depth ratio (P<0.05), the number of lamina propria lymphatic follicles (LLF, P<0.001) but to decrease in crypt depth (P=0.08) and goblet cells (P<0.0001). Moreover, a decremental ratio of n-6 to n-3 (P<0.001) and an incremental level of clove bud (P<0.05) resulted in increased relative weight of spleen. Eggshell strength was improved as a result of increasing the clove bud content (P<0.001) during the trial. Furthermore, a decline in the n-6 to n-3 ratio significantly increased (P<0.05) egg production both during the first 35-d and over the whole trial period. Similarly, increasing the clove bud content led to increase (P<0.05) in egg production and egg weight as well as improve (P<0.05) in the feed conversion ratio. In conclusion, the present findings indicate that the interactive effects of clove bud bioactive components and the highly polyunsaturated fatty acids (HUFA) may improve the performance of laying hens by fortifying mucosal and systemic immune functions as well as health indices of intestinal absorptive area.