The epigenetic impact of weaning on craniofacial morphology during growth

Miniature pigs (Sus scrofa) were used as a model to investigate whether the time of weaning (a nongenetic factor) affects skeletal growth rates for both pre- and postweaning time periods. Control litters were weaned at the normal time of 32 days. Two litters were weaned early (at 20 days) and two late (at 46 days). We digitized cranial landmarks from radiographs taken three times a week for a total of 70 days. We used analysis of covariance to test for differences in growth rates between pre- and post-weaning periods, as well as differences in growth rates among treatments. In both the late weaned pigs and the controls, facial length, facial width, basicranial length, and basicranial width growth rates slowed significantly at the time of weaning. However, in the early weaned pigs, there were no significant changes in growth rates for any of the facial or basicranial measurements at weaning. Furthermore, the postweaning rates of growth were different among treatments. One possible implication is that early growth rates could be under tight genetic control while later growth rates can be epigenetically regulated through nutritional changes.