Effects of access to pasture on performance, carcass composition, and meat quality in broilers: A meta-analysis.

Consumer preference for poultry meat from free-range birds is not justified by scientific evi-dence. Inconsistency in results among studies on the ef-fects of access to pasture on performance, carcass com-position, and meat quality has led to a meta-analysis to quantify effects. After identification of studies where re-sponse variables were directly compared between birds with and without access to pasture, standardized effect sizes were used to calculate differences. The effect size for growth combined according to a fixed effect model did not present heterogeneity (P = 0.116). However, with feed intake and feed efficiency, variability among studies (heterogeneity with P-values of below 0.10) was influenced by more than sampling error. Carcass yield was the only carcass component that showed hetero-geneity (P = 0.008), whereas numerous response vari-ables related to meat quality were not homogenous. The use of subgroup analysis and meta-regression to evaluate the sources of heterogeneity was limited by ill-defined explanatory variables and few values available within response variables. Consequently, between-study variability was accounted for by use of random effects models to combine effect sizes. According to these, few response variables were influenced by pasture ac-cess. Fat concentrations in breast (mean effect size = -0.500; 95% CI = -0.825 to -0.175; 11 studies; 14 comparisons), thigh (mean effect size = --0.908; 95% CI = --1.710 to --0.105; 4 studies; 5 comparisons) and drum (mean effect size = -1.223; 95% CI = -2.210 to --0.237; 3 studies; 3 comparisons) muscles were de-creased in free-range birds. Access to pasture increased (P < 0.05) or tended to increase (P < 0.10) protein concentrations in the respective commercial cuts. It is concluded that factors other than enhanced meat qual-ity could be responsible for consumer preference for meat from free-range poultry. [ABSTRACT FROM AUTHOR]