Antioxidant, antibacterial, and antiviral effects of two essential oils, their components, and caffeic acid for use as feed additives in poultry

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University of Delaware
To search for a potential feed additive as an antibiotic alternative for poultry production, two essential oils, thyme and cinnamon bark oil were evaluated along with their respective components as well as the common phenolic acid, caffeic acid by in vitro and in vivo experiments. In an oxygen radical absorbance capacity (ORAC) assay, caffeic acid, thymol, and thyme oil proved to be better antioxidants compared to carvacrol, cinnamaldehyde and cinnamon bark oil. Using an antimicrobial assay with a growth indicator, minimum inhibitory concentrations (MICs) were determined to be 2.0, 0.4, 0.78, 0.84, 1.54, and 1.83 mg/mL for caffeic acid, thymol, carvacrol, cinnamaldehyde, cinnamon bark oil, and thyme oil, respectively against Salmonella enterica serovar Typhimurium. Lower MICs were recorded for Salmonella enterica serovar Kentucky, Salmonella enterica serovar Enteritidis Nalr, and Salmonella enterica serovar Senftenberg. These compounds were not cytotoxic in chicken embryos and they were effective at inactivating Newcastle Disease Virus (NDV). Since thymol and thyme oil were effective antioxidant, antimicrobial, and antiviral agents based on the three assays so they were used as feed additives in three feeding trials. After a 28-day feeding trial, dietary thymol and thyme oil did not affect broiler growth performance and conversion efficiency compared to the control. Histopathology results indicated that supplementation did not cause significant lesion growth in kidney, liver, intestine and ceca samples. However, the supplementation increased the serum hydrophilic antioxidant status of the chickens. Although the addition of thymol showed no significant inhibition against cecal Salmonella for chicks inoculated with 104 and 108 CFU/mL nalidixic acid-resistant Salmonella, the highest concentration of thymol (4g/kg) demonstrated some protective effects for SPF chicks against S. Enteritidis Nalr preventing mortality.