Additional data was collected to account for possible effects of other factors (i.e. sow-, reproduction-, weight- and time-related variables) in the analysis. Next to their EBVma's, it was recorded whether sows were either primiparous or multiparous. During the behavioural observations, the total number of piglets born, the total number of piglets born alive and the number of stillborn piglets were recorded. Piglets were weaned 3 weeks after parturition and weaning survival was calculated at this time, as the number of piglets alive at weaning divide by number of live born piglets ± cross-fostered piglets. All sows (including non-experimental sows) in the farrowing house could be used for cross fostering, which took place according to litter size and piglet birth weight after the behavioural observations.
For parturitions that ended during the day (between 07:00 and 17:00 h), individual piglet weights were collected immediately after the behavioural observations and for parturitions that ended during the night (between 17:00 and 07:00 h), these weights were collected immediately after 07:00 h the next morning. From individual piglet weights, litter birth weight (kg), mean piglet birth weight (kg) and standard deviation of mean piglet birth weight (kg) were calculated. Time-related variables were time of day at which parturition took place, duration of parturition (h), mean inter-piglet interval (min) and standard deviation of mean inter-piglet interval (min).