Number of cows per maternal lactation group, average standardized production and age at first calving of the cow generating the observation.

Average maternal milk production within maternal group and age of the dam when the offspring was born. Standard deviations are given in parentheses.
1individuals born from pregnancies in non lactating mothers (heifers) were grouped together (0), and all others were classified according to the tenth-percentiles of the milk production (kg) of the dam at conception.