The calcium content of milk from 2 breeds of dairy cows (Holstein and Normande) was observed during a complete lactation. The cows were reared in 2 feeding systems providing 2 levels of feeding: an intensive system based on corn silage and pasture supplemented with concentrate and a grass system based on preserved grass silage and pasture and no concentrate. Normande cows had higher milk calcium content than Holstein cows. There was no significant variation in total milk calcium content according to system of feeding over the whole lactation. However, in winter, calcium content was reduced in the “Grass system”. Milk calcium content evolved according to stage of lactation and season, with minimum milk calcium content usually occurring in May and June. The effect of season may be related to the maximum daily temperature and the duration of the day. In conclusion, many factors (nature of forage, breed, season…) seem to impact on milk calcium content.