**Background:** Intramuscular fat (IMF), also known as marbling, is a key determinant of beef quality, affecting juiciness, tenderness, and flavor. Vitamin A is a fat-soluble vitamin essential for vision and physiological functions in cattle, and it has been implicated in adipocyte differentiation. Previous studies on the relationship between vitamin A and IMF have yielded inconsistent results, with some showing that limiting vitamin A intake increases marbling and others finding no significant effect. This meta-analysis aimed to synthesize the available evidence to clarify the relationship between vitamin A and intramuscular fat content in beef cattle.
**Methods:** The meta-analysis was conducted following PRISMA guidelines. A systematic search of MEDLINE and Ovid databases was performed from inception to November 30, 2021, using the search strategy: (((beef[Title/Abstract]) AND (Intramuscular fat[Title/Abstract])) AND (vitamin[Title/Abstract])). Only English-language articles were considered. Inclusion criteria were: (1) studies evaluating effects of vitamin A on IMF in cattle; (2) use of IMF percentage and/or IMF score as outcome measures; (3) reporting of results for both vitamin A and control groups; and (4) extractable or calculable data on group size, mean, and standard deviation. Exclusion criteria included non-extractable data, case reports, reviews, letters, conference abstracts, non-bovine studies, absence of a control group, and duplicate or overlapping study populations. Two independent researchers performed screening and data extraction. Standardized mean differences (SMDs) with 95% confidence intervals (CIs) were calculated for IMF percentage and IMF score. Heterogeneity was assessed using Cochran's Q and I² statistics. Publication bias was evaluated using funnel plots and Deek's test. Sensitivity analysis was performed by omitting one study at a time.
**Key Results:** The database search identified 152 articles. After removing 50 duplicates and excluding 91 studies through initial screening, 11 articles underwent full-text assessment. Four studies were excluded due to limited information, leaving 7 articles for inclusion. No additional studies were identified through bibliography screening. The risk of bias for included studies was assessed as low. For IMF percentage, the pooled SMD was -0.78 (95% CI -2.68 to 1.12, p = 0.419). For IMF score, the pooled SMD was 1.25 (95% CI -2.75 to 5.25, p = 0.539). Neither outcome reached statistical significance. Significant heterogeneity was observed: for IMF percentage, Q = 246.84 (p < 0.01) and I² = 97.6% (p < 0.01); for IMF score, Q = 87.20 (p < 0.01) and I² = 97.7%. Deek's tests for publication bias yielded p-values of 0.535 for IMF percentage and 0.281 for IMF score, indicating no significant publication bias. Sensitivity analysis showed no outlier studies, and the pooled results remained robust after sequential omission of individual studies.
**Clinical Implications:** This meta-analysis suggests that vitamin A supplementation may decrease intramuscular fat in beef cattle steers, though the results did not reach statistical significance. The high heterogeneity (I² > 97% for both outcomes) indicates substantial variability across studies, which could not be explored through subgroup analysis or meta-regression due to the limited number of eligible studies. The authors note that retinoic acid, a vitamin A metabolite, may inhibit adipocyte differentiation and regulate growth hormone expression, providing a biological rationale for the observed effects. However, the non-significant findings and significant heterogeneity limit the strength of conclusions. The authors call for more well-designed trials to further investigate this relationship. For commercial beef production, these findings suggest that manipulating vitamin A levels could potentially influence marbling, but the evidence is currently insufficient to support specific dietary recommendations.