*Global Perspectives of Intensive Animal Farming and Its Applications DOI: http://dx.doi.org/10.5772/intechopen.112271*

Q test. The variation across studies was observed by the forest plot as well as the inverse variance index (I2). Values of I2 (25, 50, and 75%) were considered as low, medium, or high heterogeneity, respectively. In this meta-analysis, the heterogeneity value was >75%, therefore, the DerSimonian and Laird random effects models with 95% CI. Funnel plot analysis was carried out if heterogeneity was of moderate to high level. Subgroup meta-analyses were then employed by publication year.
