Effects of Essential Oils on Calf Growth, Ruminal Fermentation, and Antioxidative Status: A Meta-Analysis

Wei Li¹Fang Wang²Ben Li³Fang Sun⁴Chunhai Liu⁵Yuanfang Zhu⁴Peng Zhong^4*

• ¹Livestock Veterinary Branch, Heilongjiang Academy of Agricultural Sciences, China, Qiqihar city, China
• ²College of Life Sciences and Agroforestry, Heilongjiang Provincial Key Laboratory of Resistance Gene Engineering and Protection of Biodiversity in Cold Areas, Qiqihar University, China, Qiqihar city, China
• ³Medical College of Jinzhou Medical University, Jinzhou, Liaoning Province, China
• ⁴Livestock Veterinary Branch, Heilongjiang Academy of Agricultural Sciences, China, Qiqihar, China
• ⁵Liaoning Feidi feeding technology co., ltd, Xingcheng, China

Essential oils (EO) have attracted much attention in the calves industry due to their favorable antimicrobial properties. This meta-analysis aimed to determine the efficacy of EO on the calves to provide better guidance for cattle feed. We comprehensively searched relevant studies published from inception to February 06, 2022, in the four electronic databases: PubMed, CENTRAL, Web of Science, and EMBASE, were comprehensively searched. The quality of included studies was evaluated using the "Collaborative Approach to Meta-Analysis and Review of Animal Data from Experimental Studies" (CAMARADES) checklist with ten items. We used the weighted mean difference as the effect size for the continuous variables. Summary risk ratios (RR) were presented if the results were binary variables and presented summary risk ratios (RR) for binary variables. Additionally, we performed subgroup and sensitivity analyses. This systematic review and meta-analysis of 10 animal studies with 226 calves. The average quality score was 5.8, ranging from 5-7. EO improved milk production (WMD=0.30; 95% CI 0.13 to 0.47; I 2 =0%, P=0.985)and beta-hydroxyl butyric acid (WMD=0.01; 95% CI 0.04 to 0.16; I 2 =0%, P=0.472).However, EO did not significantly improve rumen fermentation characteristics or overall performance index. These findings suggest that while EO may have some beneficial effects on specific outcomes like milk production and beta-hydroxybutyric acid levels, its impact on rumen fermentation and overall performance remains inconclusive. A larger-scale randomized controlled trials(RCT) would better assess the effect of EO on the efficiency of ruminal fermentation, anti-oxidative status, and performance.