Effects of dietary thyme essential oil on hemato-immunological indices, intestinal morphology, and microbiota of Nile tilapia
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Thyme (Thymus vulgaris) essential oil (TVEO) is a herbal medicine with one of the highest levels of antimicrobial activity. Although TVEO has been broadly used in poultry and swine production due to its immunostimulatory and growth-promoting characteristics, the effects of TVEO on fish are poorly characterized. In this study, Nile tilapia (Oreochromis niloticus L.) were fed 0, 0.1, 0.5, and 1% TVEO for 15 days. Subsequently, blood parameters, intestinal morphology, and the population of Bacillus bacteria in the intestine were evaluated. The numbers of lymphocytes (p < 0.05) and leukocytes (p < 0.05) significantly increased in the blood of the fish fed the highest dose of TVEO. Based on the normal behavior of the fish and the alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, which were not altered (p > 0.05), this study concluded that the diets were safe and showed no negative or toxic effects. Even at doses as high as 1%, TVEO did not alter the population of beneficial Bacillus bacteria in the gut. In conclusion, supplementation with TVEO stimulated the cellular components of the non-specific immune response of Nile tilapia without causing deleterious effects or altering the population of important intestinal bacteria.
KeywordsBacillus Herbal medicine Immunostimulant Innate immunity Plant extract
The authors thank Dra. Vany P. Ferraz (Chromatography Laboratory, Department of Chemistry, UFMG) for the assistance with the analysis of the EOs. The manuscript was edited for proper English language, grammar, punctuation, spelling, and overall style by one or more of the highly qualified native English speaking editors at American Journal Experts.
This work was supported by grants from the National Council for Scientific and Technological Development-CNPq (140487/2014-0), and the São Paulo Research Foundation-FAPESP and the Coordination of Superior Level Staff Improvement-CAPES (2014/14039-9).
Compliance with ethical standards
The experiment was approved by the Ethics Committee on the Use of Animals (CEUA) of the School of Agricultural Sciences and Veterinary Medicine at Universidade Estadual Paulista (UNESP), Jaboticabal, SP, Brazil, under protocol number 13019/15. The approval was consistent with the ethical principles adopted by the Brazilian College of Animal Experimentation.
Conflict of interest
The authors declare that they have no conflict of interest.
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