Dairying implies the keeping of a large number a mature females. The mortality profile is thus clearly marked by the presence of old individuals, essentially cast milking cows. It has also been suggested that the profit of the whole milk production for the herders requires the slaughter of the young animals. However, iconographical and ethnographical evidence allows the assumption that in primitive domestic bovines the presence of the calf might have been necessary for the cow assent to give her milk. The young should thus not be slaughtered before the end of the lactation period. Some kill-off pattern established on neolithic cattle remains in Paris Basin display features fitting with what has been defined as a "post-lactation slaughter". An isotopic study of collagen preserved in cattle bone remains from Bercy (Paris, IVth mil. BC) shows that the young individuals belonging to the over-represented age group in this site were actually slaughtered around weaning age.