“Evaluating the Alternative Use of Phytogenics as Feed Additives: Effects on Growth Performance and Immune Response in Newcastle Disease-Vaccinated Broiler Chickens
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Date
2025
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Addis Abeba University
Abstract
Background: Phytogenic feed additives (PFAs) a group of medicinal plants and their essential oils—are increasingly used in poultry sector due to their biologically active compounds that promote animal health, enhance immune function, stimulate growth, boost productivity and reduce mortality. This study aimed to evaluate the effects of dietary PFAs on the growth performance and immunological response of broiler chickens to Newcastle disease (ND). Methods: Experimental study was conducted on a total of 200 Cobb 500 chicks. The chicks were randomly assigned to six groups, with each group comprising three replicates of 10 chicks. To establish baseline immunological data, 20 chicks were bled before the experiment. One treatment group (G4) received only basal diet, while the remaining groups (G1, G2, G3, G5, and G6) were supplemented with 2% of specific phytogenics: thyme (Thymus vulgaris, G1 and G6), lemongrass (Cymbopogon schoenanthus, G2), and rosemary (Rosmarinus officinalis, G3). Additionally, G5 received a commercially available vitamin supplement commonly used by medium-scale poultry farms. Throughout the 42-day study period, mortality, feed conversion ratio (FCR), body weight
gain (BWG), and feed intake were recorded. Serological tests were conducted on three representative chickens per replication to assess antibody responses by ELISA test. Results: The findings of this study demonstrated that the inclusion of PFAs to the diet had no significant effect on overall feed intake. Body weight (BW), BWG, and average daily weight gain (ADWG) did not differ significantly among groups during the starter and grower stages. However, by day 42, G2 and G5 exhibited significantly greater final BW, overall BWG, and ADWG (p < 0.01) compared to the other groups. Over the study duration, G5 chickens achieved the best FCR, followed by G2 and G4. Serological results showed that on day 42 of the trial, the G3 and G5 chickens had a higher antibody titer against the ND vaccination. These findings suggested that adding 2% of this PFA leaf powder to broiler diets had no detrimental effects on feed consumption, while emongrass inclusion enhances growth performance (BW and ADWG) and FCR similarly to commercially available vitamins. However, the inclusion of these dietary PFAs did not significantly influence immune organs development. Rosemary inclusion into the diet and supplementing vitamins improved the immune status of broiler chickens against ND. Conclusion: The selected herbs, particularly lemongrass and rosemary, may be used as effective natural alternatives to synthetic supplements by improving growth performance and immune response in broiler chickens. Further research is needed to fully elucidate their potential as substitutes for antibiotic growth promoters in commercial poultry production
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broilers, immune response, growth performance, PFAs