Introduction: Essential oils (EO) have gained significant attention in the calves industry due to their antimicrobial properties. This meta-analysis aimed to evaluate the efficacy of EO on calves to provide better guidance for cattle feed.Methods: We conducted a comprehensive search of relevant studies published from inception to February 6, 2022, using PubMed, CENTRAL,Web of Science, and EMBASE. The quality of included studies was assessed using the CAMARADES checklist. Effect sizes were calculated using weighted mean differences (WMD) for continuous variables and summary risk ratios (RR) for binary variables. Subgroup and sensitivity analyses were also performed.Results: This systematic review and meta-analysis included 10 animal studies with 226 calves. The average quality score was 5.8 (range: 5–7). EO improved milk production (WMD = 0.30; 95% CI 0.13 to 0.47; I² = 0%, p = 0.985) and beta-hydroxybutyric acid levels (WMD = 0.01; 95% CI 0.04 to 0.16; I² = 0%, p = 0.472). However, EO did not significantly improve rumen fermentation characteristics or overall performance index.Discussion: While EO may have beneficial effects on specific outcomes like milk production and beta-hydroxybutyric acid levels,its impact on rumen fermentation and overall performance remains inconclusive. Future large-scale randomized controlled trials (RCTs) are needed to better assess the effects of EO on ruminal fermentation efficiency, anti-oxidative status, and overall performance.

Background: Selection for fall dormancy (FD) in alfalfa (Medicago sativa) can impact other traits, including dry matter yield (DMY), winter survival rate (WSR) and nutrient compositions. The current study was aimed to screen alfalfa varieties with greater yield, good quality and strong winter survival ability and thus are more suitable for planting in Heilongjiang, China and may be suitable for similar upper-latitude semiarid environments in the world. Methods: Eight alfalfa varieties (Zhaodong, Gongnong No. 2, Caribou, Gold Empress, Adrenalin, Sanditi, Sardi and WL525) were planted in regional test based on randomized block design and mowed during the early flowering stage from 2019 to 2021. The DMY, WSR and nutrient compositions were measured by weighing method, field investigation and chemical test, respectively. Result: There was a significant negative correlation (P less than 0.01) between the FD rating and WSR, with a correlation coefficient of 0.956. The three-year average DMY of Gongnong No. 2 was the greatest (12,745.65 kg ha-1) and there was a significant negative correlation (0.766, P less than 0.01) between the FD rating and DMY. The crude protein content of Gongnong No. 2 was greater (19.29%) than the other varieties. The Zhaodong had the least neutral detergent fiber (47.76%) and acid detergent fiber (30.79%).