Growth during the late fattening period (montanera) of 762 Iberian pigs has been analyzed using linear production functions obtained from 2663 weight records. Two adjustment procedures of the linear function parameters (intercept, weight after 60 days of montanera and slope, daily gain during the montanera) have been compared, either previous or joint with the evaluation model effects. A strong correlation was observed between the estimates of these parameters obtained by the two procedures but the results confirmed the capacity of the joint ajustment to decrease the influence of outliers on slope estimates. For both adjustment methods, two different evaluation models have been used, with and without the inclusion of a common environmental effect. The inclusion of this effect reduced additive variance and heritability of intercept and slope. The h² values, close to 0.5, indicate the easy modification of both parameters by selection. Finally, the influence of the adjustment method on the ranking of estimated breeding values has been studied , which is mainly relevant for breeding animals with scarce or aberrant information.