Objective: The purpose of this meta-analysis was to evaluate the effect of dietary essential oils (EOs) on productive performance, nutrient digestibility, and serum metabolite profiles of broiler chickens and to compare their effectiveness as growth-promoting additives against antibiotics.Methods: Peer-reviewed articles were retrieved from Web of Science, Science Direct, PubMed, and Google scholar and selected based on pre-determined criteria. A total of 41 articles containing 55 experiments with 163 treatment units were eligible for analyses. Data were subjected to a meta-analysis based on mixed model methodology considering the doses of EOs as fixed effects and the different studies as random effects.Results: Results showed a linear increase (p<0.001) on body weight gain (BWG) where Antibiotics (FCR) and average daily feed intake decreased (p<0.001) linearly with an increasing dose of EOs. Positive effects were observed on the increased (p<0.01) digestibility of dry matter, crude protein, ether extract, and cecal Lactobacillus while Escherichia coli (E. coli) population in the cecum decreased (p<0.001) linearly. There was a quadratic effect on the weight of gizzard (p<0.01), spleen (p<0.05), bursa of fabricius (p<0.001), and liver (p< 0.10) while carcass, abdominal fat, and pancreas increased (p<0.01) linearly. The dose of EOs linearly increased high density lipoprotein, glucose, protein, and globulin concentrations (p<0.01). In comparison to control and antibiotics, all type of EOs significantly reduced (p<0.001) FCR and tended to increase (p<0.1) BWG and final body weight. Cinnamaldehyde-compound was the only EOs type showing a tendency to increase (p<0.1) carcass weight, albumin, and protein of serum metabolites while this EOs together with EOs-Blend 1 decreased (p<0.01) E. coli population. Low density lipoprotein concentration decreased (p<0.05) with antibiotics and carvacrol-based compound when compared to the control group.Conclusion: This evidence confirms that EOs are suitable to be used as growth promoters and their economical benefit appears to be promising.
The objective of this meta-analysis was to elucidate whether there are general underlying effects of dietary tannin extract supplementation on rumen fermentation, digestibility, methane production, performance, as well as N utilisation in ruminants. A total of 70 papers comprised of 348 dietary treatments (from both in vivo and in situ studies) were included in the study. The database was then statistically analysed by the mixed model methodology, in which different experiments were considered as random effects and tannin-related factors were treated as fixed effects. The results revealed that an increased level of tannin extract inclusion in the diet lowered ruminant intake, digestibility, and production performance. Furthermore, the evidence also showed that an increased level of tannin extract decreased animal N utilisation where most of rumen by-pass protein was not absorbed well in the small intestine and directly excreted in the faeces. Due to the type of tannin extract, HT is more favourable to maintain nutrient intake, digestibility, and production performance and to mitigate methane production instead of CT, particularly when supplemented at low (<1%) to moderate (~3%) levels.
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