Synergetic effects of essential oils mixture improved egg quality traits, oxidative stability and liver health indices in laying hens fed fish oil

Omega-3 fatty acids are necessary for human health, although products containing higher proportions of these fatty acids make them more susceptible to lipid peroxidation. The current study was conducted to evaluate the synergetic effects of dietary supplementation of herbal essential oils mixture (Thymus vulgaris, Mentha piperita, Rosmarinus officinalis and Anethum graveolens) and dietary fat sources on egg quality traits, oxidative stability and liver health indices of laying hens. A total of 150 laying hens were randomly distributed among 6 experimental treatments with five replicates of five birds each. Dietary treatment consisted of three levels of herbal essential oils mixture (0, 100 and 200 mg/kg) and two sources of fat (fish oil and soybean oil containing different ratios of n-6 to n-3 fatty acids) that fed during an 80 d feeding trial. The results showed that administrating fish oil, containing low ratio of n-6 to n-3 fatty acids, enhanced liver (P < 0.05) malondialdehyde concentration, egg yolk color (P < 0.05), and led to the reductions in liver relative weight, hepatic lipid percentage (P < 0.05), serum alkaline phosphatase activity (P < 0.01), as well as serum and egg yolk cholesterol contents (P < 0.05). Moreover, herbal essential oils mixture resulted in the declines in blood cholesterol and triglyceride concentrations (P < 0.01), enzymes activity of alanine aminotransferase and aspartate aminotransferase (P < 0.01), as well as hepatic and serum malondialdehyde concentrations (P < 0.05). Also, it caused the improvements in eggshell hardness and thickness (P < 0.05). In general, the findings indicated that although dietary administration of fish oil increased the susceptibility of serum and liver to lipid peroxidation, feeding 200 mg/kg essential oils mixture resulted in the best systemic and hepatic antioxidant responses, the modulated serum lipid profiles, and also the improved eggshell quality.