Modelling growth in Suffolk and Charollais sheep populations using random regression models and validation of constrained polynomial correlation values

•Can random regression models be applied to growth in sheep with few mature records?•Can models with constrained parameters produce valid genetic values?•Does a multitrait validation procedure support the chosen parameter correlation?•Models with constrained parameters at 0.5 results in heritability values from 0.18 to 0.5.•This research may extend genetic evaluation to more of the animal production sector.