The present study investigates the gap between the daily milk production potential and the effective milk yields in six herds. These two parameters and their changes were observed in the Gharb irrigation scheme (northwest of Morocco), during a five months study period. They were analyzed in relation to the changes in the rations of the cows and in their live weights. Results reveal that under conventional cattle rearing conditions in Morocco, i.e. the vast majority of smallholder units and farms with an area less than 20ha, dairy production suffers from numerous setbacks. One of the most evident is farmer's lack of knowledge of cows’ dietary requirements and their changes throughout the lactation period. Moreover, dairy farmers seem to ignore the changes in forages net energy, rumen degradable and metabolizable protein contents, which induce many errors in providing concentrate supplements. Results also show that the effective milk yield is often inferior to the lactation potential, given the limited availability of forage coupled to errors in rations formulation. Finally, the results emphasize the need to reconsider the use of high genetic merit cows, because of their rising prices, in farms characterized by erratic fodder availability coupled to the absence of balanced rations formulation. Manuscript profile