The interest in the search for alternatives to antibiotics in poultry production has been increasing, especially with the focus on essential oils due to their remarkable bioactive properties. This study aimed to investigate the effects of dietary supplementation of essential oils on the performance and gut morphometry of broilers, by using an approach of systematic review and meta-analysis. In the conduction of the systematic review, three electronic databases (PubMed, Science Direct and Scielo) were consulted in January 2023. Out of an initial amount of 162 papers, only 27 met the requisites to be included in the database. Furthermore, after the use of established criteria for the meta-analysis, only 16 papers were qualified for the evaluation of the aimed parameters. In the meta-analysis, it was observed that the supplementation had significant impact (P < 0.05) of 2.88% in weight gain, in comparison to the basal diet. In addition, the supplementation of essential oils significantly improved (P < 0.05) gut morphometry parameters such as villus height in the ileum (15.66% higher), and 8.26% increase in the villus height to crypt depth ratio in jejunum compared to the basal diet. Dietary essential oils improve the growth performance and gut histomorphometry of broilers, even when combined with antibiotics as growth promoters.

The aim of this study was to test the hypothesis of an improved growth, dietary nutrient availability and overall health of broiler chickens reared on recycled litter when fed a standardised combination of essential oils (EO; carvacrol, cinnamaldehyde and capsicum oleoresin). To assess the effect of dietary treatments, feed intake, weight gain, feed efficiency, availability of dietary nutrients and energy, villus morphometry, excreta sialic acid concentration, hepatic antioxidants and serum amyloid A (SAA) when fed to broiler chickens were evaluated. Counts of Eimeria spp. oocysts were also determined in excreta samples. Four experimental diets were offered, including two basal control diets based on either wheat or maize that contained 215 g CP/kg and 12.13 MJ/kg metabolisable energy and another two diets using the basal control diets supplemented with the EO combination at 100 mg/kg diet. Each diet was fed to eight floor pens, containing two birds each, following randomisation. Birds fed the EO-supplemented diets had an improved (P<0.05) feed conversion ratio (FCR). Birds fed maize-based diet had an improved daily weight gain and FCR (P<0.05) compared with wheat-fed birds. Wheat-based diet tended (P=0.056) to have greater N-corrected apparent metabolisable energy and had greater fat retention coefficient (P<0.05) compared with maize-based diets. No differences (P>0.05) were observed in villus morphometry, sialic acid secretion, number of oocysts and SAA. Feeding the EO improved (P<0.05) the retention of dietary Ca and Na. Compared with maize, feeding wheat-based diets improved the retention coefficients for Ca, P and Na (P<0.05). Feeding dietary EO improved (P<0.05) the concentrations of the hepatic antioxidants, including carotene, coenzyme Q10 and total vitamin E. The hepatic concentration of carotene of the maize-fed birds was 55.6% greater (P<0.05) compared with the wheat-fed birds. These results demonstrated that the addition of a standardised combination of EO in wheat- and maize-based diets provided benefits in terms of feed efficiency, mineral retention and antioxidant status of the birds when reared on recycled litter.

During the past fifteen years, phytoadditives in animal nutrition have attracted attention for their potential role as alternatives to antibiotic growth promoters. The goal of this paper is to review the current scientific data on the use of phytoadditives in broiler nutrition. The efficacy of phytogenic applications in broiler nutrition depends on several factors, such as composition and feed inclusion level of phytogenic preparations, bird genetics, and overall diet composition. Difficulty arises when comparing different studies using phytoadditives due to the large variation in composition and sourcing, thus the potential biological effects of phytogenic compounds may differ. However, a great amount of research data supports a potential role of phytoadditives as natural, non-antibiotic growth promoters in broiler nutrition. The mechanisms behind growth promotion are far from being elucidated, as data on phytoadditive effects on nutrient digestibility, gut function and the immune system are still scarce. Phytogenic intake may certainly depress pathogen growth in the gut, however an understanding of their effects on the complex gut ecosystem is still far from clear. There is insufficient amount of studies describing the effects of phytoadditive dietary intake on carcass meat safety, whereas the beneficial effect of phytogenics on carcass meat quality is very well documented. As the last point of this review, further considerations on the efficient applications of phytoadditive compounds in broiler nutrition are given.