Effects of Dietary Betaine on Growth Performance, Serum Metabolites, and Meat Quality of Pigs: A Meta-Analysis.

Betaine, functioning as a key methyl donor and organic osmolyte, is widely used to improve growth performance and carcass characteristics of swine. However, existing studies show inconsistent results, and the optimal supplementation dose remains unclear. This study systematically quantified the impact of betaine supplementation on the growth performance, serum metabolites, and meat quality of swine via a meta-analysis and meta-regression of 31 randomized controlled trials. The standardized mean differences (SMDs) were calculated using a random-effects model, while a subgroup analysis and meta-regression were used to investigate potential sources of heterogeneity. The analysis revealed that dietary betaine supplementation significantly increased the average daily gain and reduced the feed conversion ratio, while the average daily feed intake remained unaffected. A subgroup analysis indicated that the optimal dose for improving feed conversion was approximately 1250 mg/kg, whereas this efficacy was attenuated in the high-dose cohorts. Furthermore, betaine significantly reduced serum urea levels, muscle shear force, drip loss, and cooking loss. Conversely, the backfat thickness and serum lipid indices showed no significant changes. The meta-regression confirmed that the breed and growth stage were the primary determinants of heterogeneity in growth performance. These findings demonstrate that betaine facilitates growth primarily by enhancing feed efficiency and protein accretion, and its beneficial effects on meat quality are mainly driven by improved tenderness and water-holding capacity.