Effect of growth and plane of nutrition on apparent muscle fiber numbers in the pig
A histological sampling technique was used to estimate the number of muscle fibers appearing in transverse sections of whole sartorius muscles. Transverse sections were taken at the midlength of sartorius muscles from pigs growing at a rate of approximately 0.7 kg/day. Between 56 and 168 days (postnatal), the apparent number of muscle fibers increased at an approximate rate of 300 fibers/day. No evidence of the formation of new muscle fibers by myoblast fusion or muscle fiber fission was detected by light microscopy. Animals placed on a maintenance diet which prevented growth for 28-day periods prior to slaughter showed a fixation or decrease in apparent numbers of muscle fibers. These data support the hypothesis that the arrangement of muscle fibers during growth of the porcine sartorius muscle is a dynamic rather than a fixed system.