Maternal constraint influences muscle fibre development in fetal lambs

Abstract

The objective was to examine myogenesis in two situations expected to be characterized by maternal constraint: (i) in fetuses due to be born in spring (n = 10) or autumn (n = 10); and (ii) in single (n = 16) and twin (n = 20) fetal lambs. Maternal constraint operating through limitation of placental size, as measured by placentome weight per fetus, was evident in each study. Although a lower placental weight did not inßuence body and muscle weights of fetuses due to be born in the spring or autumn, twins had lower body and muscle weights than singles. Fibre number and average bre cross-sectional (CS) area were differentially affected by season and fetal number. The differences in muscle bre morphology between spring- and autumn-born fetuses suggest that muscle bre development was inßuenced by maternal constraint in the absence of an effect on fetal weight. The differences in muscle bre number and CS area in particular muscles from twin and single fetuses suggest that more severe maternal constraint, reßected in a lower placental size per fetus, not only inßuences fetal weight but can also affect muscle development.