Feed efficiency of lactating Holstein cows is repeatable within diet but less reproducible when changing dietary starch and forage concentrations

•We evaluated dietary starch on the reproducibility of feed efficiency in dairy cows.•Feed efficiency was less reproducible across diets than repeatable within diets.•Correlation coefficients were lower across diets compared to that in the same diet.•Error of repeatability was higher across diets compared to that in the same diet.•Feed efficiency is more likely to change after a diet change than over lactation.