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