Market-age growth performance following in-ovo interventions in commercial broilers: A meta-analysis

In-ovo intervention has been investigated as an early-life strategy to influence post-hatch development, but its effects on growth performance at commercial market age remain inconsistent. This meta-analysis aimed to quantitatively synthesize BW, feed conversion ratio (FCR), and breast muscle yield at d 35 and d 42 in commercial broilers. A total of 1,409 records were identified in the initial database search, of which 38 studies met the eligibility criteria. Random-effects meta-analyses were conducted separately according to assessment age and comparator, while broiler strain, intervention category, and injection timing were explored as potential sources of heterogeneity. Compared with Non-injection, In-ovo intervention was associated with higher BW on d 35 (Hedges's g = 0.686, 95% CI: 0.066 to 1.306, P = 0.03, I² = 84.55%, n = 12) and d 42 (Hedges's g = 0.811, 95% CI: 0.086 to 1.536, P = 0.028, I² = 86.71%, n = 13), and lower FCR on d 35 (Hedges's g = -0.358, 95% CI: -0.671 to -0.044, P = 0.025, I² = 21.67%, n = 11) and d 42 (Hedges's g = -0.565, 95% CI: -0.852 to -0.277, P < 0.001, I² = 0%, n = 10). Compared with Control-sham, significant pooled effects were detected only for BW on d 42 (g = 0.420, P = 0.042) and FCR on d 35 (g = -0.274, P = 0.036), but not for BW on d 35 or FCR on d 42. No significant pooled effect was detected for d 42 breast muscle yield compared with Control-sham (Hedges's g = -0.041, 95% CI: -0.27 to 0.188, P = 0.724, I² = 5.58%, n = 6) or Non-injection (g = -0.153, P = 0.291). Exploratory subgroup analyses identified significant between-subgroup differences by broiler strain and intervention category in selected BW and FCR comparisons (P = 0.006-0.030). Injection timing was significantly associated with d 42 FCR effect size relative to Control-sham (β = -0.1663, P = 0.0004), but not with other analyzed outcomes. No significant pooled differences in BW or FCR were detected between Control-sham and Non-injection. Overall, these findings provide quantitative evidence of potential market-age benefits from In-ovo interventions, while highlighting the need for standardized experimental designs and independent validation of specific intervention conditions to support reliable commercial application.