Effects of low birthweight on postnatal development of skeletal muscle in the pig

Abstract

The aim of this work was to investigate the effects of low birthweight within litters of pigs on the development of skeletal muscle, as observed at the level of the light and electron micro¬ scope, and to relate these effects to general body growth and potential for meat production. An increase in body weight after birth imposes ever-increasing demands on muscle metabolism and by observing its inherent adaptation in animals of different birthweights some of the phenomena affecting muscle development were revealed.This study was based on 49 purebred Large White pigs of vari¬ ous ages between birth and 128 days, ranging in liveweight from 650g to 49500g; 35 of these animals were sucklers. The pigs came from a total of 17 litters. Littermates were slaughtered at the same age and were chosen by their weight at birth. The largest male (average birthweight of 1 54 4g) and the smallest male (average birthweight of 1144g) littermates were selected together with any "runt' pigs of 950g or less (average birthweight of 7 7 B g) .During the course of this study muscle fibre anomalies were evident in the form of 'giant' fibres. Data collected on their occurrence, histochemical and ultrastructural characteristics are reported and discussed.A study of the prenatal skeletal muscle development of mice bred for disparate liveweights at 6 weeks of age was also per¬ formed. The results of this preliminary study suggested that, in a genetically small strain of mice, the relatively lower muscle fibre number evolves through a reduced primary fibre population only, secondary fibre number being unaffected.