Methionine and Cysteine are usually the first performance limiting amino acids in broiler feeds and commonly DL-methionine (DL-Met, 99% purity) or methionine hydroxy analogue (MHA; free acid: MHA-FA, 88% purity; to a much smaller extent calcium salt: MHA-Ca; 84% purity) is supplemented to meet requirements. The chemical differences between the two compounds influence their nutritional value, expressed as relative bioavailability (RBV), which has been confirmed in previous scientific publication to be at or close to 65% for MHA-FA relative to DL-Met on product-to-product basis (Lemme et al. 2020) and recently validated by Li et al. (2023). This information is also important for cost-effective purchasing of the methionine source, since the RBV should be reflected in the pricing of the products in order to realize the full value. Although only the most recent publication was mentioned, many of such 65:100 trials have been conducted over the years which can be analysed by a meta-analysis.


To perform a meta-analysis of the 65:100 trials grouping data by marginal Met+Cys supply (below recommendations), at recommended levels and clearly above recommended levels to determine whether differences in responses can be observed.


Data analysis on feed conversion ratio was performed using Meta-Essential version 1.4. The estimated effect size (the difference between DL-Met and MHA treatment) was quantified using Hedges’ g with a 95% confidence interval (CI). Data were pooled using a fixed-effect model due to the absence of heterogeneity after being pre-checked using the I2 statistic. A significant effect was declared when the overall estimated effect size had P < 0.05.


No heterogeneity was found for feed conversion data (I2 = 0.00%) allowing to estimate the true effect size in a homogeneous population. The results demonstrate that overall mean effect size values (Hedges’ g) were close to zero and confidence interval was very small, which provides clear evidence that replacement of MHA with DL-Met in a ratio of 100:65 always results in the same performance.

Table 1 - Summary of the overall effect size when data is grouped by dietary Met+Cys level

Grouping data by dietary Met+Cys level

Hedges'g (95% CI)



Above requirement

0.10 (-0.17 to 0.38)

P = 0.488


At requirement

-0.13 (-0.33 to 0.07)

P = 0.676


Below requirement

0.01 (-0.17 to 0.20)

P = 0.629



The meta-analysis provides evidence that not only MHA-FA can be replaced by DL-Met in a 100:65 ratio with no risk, but also that this conclusion is valid for any general dietary Met+Cys supply status.