Relationship between motoneuron number and myofibre number in the pig

A segment (at level T1) of spinal cord and a midbelly slice of the m. semitendinosus were removed from the largest- and smallest-birthweight littermate of each of 12 Large White pig litters sacrificed at various ages. When the ratio of myofibre numbers for large to small littermate within each litter was related to the ratio of motoneuron numbers then a significant correlation (r = 0.638, p less than 0.05) was observed. It is suggested that in utero growth retardation causes a reduction in myofibre numbers (within a litter), which in turn reduces motoneuron survival rate.