How does pregnancy and lactation affect efficiency of female mice divergently selected for post-weaning net feed intake?

Females from lines of mice divergently selected for post-weaning net feed intake maintained significant line differences in daily feed intake (0.8 g/day difference, 22%) and net feed intake (+/- 0.35 g/day respectively) both before and during pregnancy. Dam/litter units converged completely for daily feed intake immediately in the postnatal stage, during a period of negative energy balance when feed intake and rate of gain were both maximised. Feed intake net of that required for growth and maintenance of liveweight was effectively zero for both lines during this 2-week period. The lines re-diverged in late-lactation. Variance for all traits increased substantially over the 11 weeks of the experiment. In an extensive production environment, where peak lactation generally coincides with abundant pasture supply, this short convergence would have little impact on overall production efficiency. Consequently, selection for post-weaning net feed intake based on growth/weight components remains a potential means to improve production efficiency.