Recently, a number of scientific studies has concentrated on the bactericidal and bacteriostatic effects of various herbs and plant extracts. The studies have demonstrated that herbs and herbal products have a positive effect on broiler growth performance. It have reported that garlic may be used as a natural herbal growth promoter for broilers without side effects, neither for chicken performance nor consumers, and meat was not tainted with flavour or smell of garlic. Also replacing antibiotic growth promoters with herbs resulted in decreased body weights, increased feed conversion per kg of weight gain and insignificant effects on carcass yield and carcass fatness.
A study was conducted with female broilers to investigate the effects of five herbal natural feed additives as alternative to an antibiotic growth promoter. In the experiment, a total of seventy-two day-old female broiler chicks were randomly assigned to six groups containing 12 chicks each and raised from 0 to 42 d of age. The treatment groups were supplemented with antibiotic growth promoter, oregano, du-sacch, quiponin, garlic and thyme powder, respectively.
Differences in body weight gain, feed intake and feed efficiency of broilers fed diets supplemented with antibiotic growth promoter and five herbal natural feed additives were not significant from 0 to 42 d of age. In addition, some blood parameters and the concentration of E. coli in caecum were not significantly affected (P > 0.05) by the dietary treatments. The depth of crypts in ileum was significantly reduced (P < 0.05) by inclusion of garlic and thyme in diets in comparison to diets supplemented with antibiotic growth promoter, oregano and du-sacch. The feed costs per kg of weight gain in broilers fed diets supplemented with oregano, garlic and thyme was higher than in those given diets supplemented with du-sacch, quiponin and antibiotic growth promoter. Results of this experiment demonstrated that the herbal natural feed additives such as oregano, du-sacch, quiponin, garlic and thyme may be used as alternatives to an antibiotic growth promoter in broiler production.