Meta-Analyses of Methionine Source Concept Validation Trials in Broilers

Simple Summary Methionine (Met) and cysteine (Cys) are usually performance-limiting amino acids in broiler feed. To balance diets in order to meet birds' requirements, DL-Methionine (DL-Met) or the hydroxy analogue of methionine (MHA), which is a precursor of methionine, are common supplements. Based on a multitude of simultaneous dose-response trials, a 65% bioefficacy is recommended for MHA relative to DL-Met. This recommendation has often been tested under various experimental conditions. The present meta-analysis of effect sizes from 95 data sets revealed very little heterogeneity of data combined with the small effect sizes of DL-Met treatments when DL-Met replaced MHA at a weight ratio of 65:100. The effect sizes of DL-Met treatments were not different from MHA treatments, which confirms that 100 units of an MHA product can be replaced by 65 units of DL-Met without compromising performance. The data analysis also revealed that this result was not affected by the broiler strain, the diet type, or the MHA product type being used in the feeding experiments. Moreover, the broiler feeding trials supposed to challenge the 65% bioefficacy recommendation were successful at any dietary Met+Cys supply, including the most sensitive test conditions at marginal Met+Cys supply.Abstract While the supplementation of methionine (Met) sources in broiler feeds has been established for several decades, there is debate on the nutritional value of the methionine hydroxy analogue of methionine (MHA) relative to DL-Met. Based on a recommendation suggesting that MHA is 65% as effective as DL-Met, many feeding trials have been conducted to challenge this recommendation. A literature search found 25 publications contributing 95 data sets suitable to compute Hedges' g effect sizes used in the meta-analysis. The data had very little heterogeneity of almost zero and the small effect sizes of the DL-Met results were not significantly different from MHA. Data were split in various subgroups, finally suggesting that neither broiler strain (Cobb 500, Ross 308), diet type (corn, wheat based), origin of data (peer-reviewed, grey literature), nor MHA product (MHA-free acid, MHA-calcium salt) impacted the outcome of the meta-analysis. Moreover, distinguishing data in groups with dietary Met+Cysteine (Cys) levels below, at, or above requirement demonstrated that there was no interaction with general Met+Cys supply. It is therefore concluded that MHA products can be replaced by DL-Met in a weight-to-weight ratio of 100:65 in any production condition without compromising broiler performance