Muscle cellularity and postnatal growth in the pig.
Fast-growing strains of pigs and of other animals tend to have more muscle fibers than do slow-growing strains. The relationship between fiber number and growth rate was extended by examining pigs within the same strain. Seven litters of pigs (n = 66) were weighted at monthly intervals from birth to approximately 80 kg. The semitendinosus muscle was removed and an estimation of total fiber number, total primary fiber number, and mean secondary:primary fiber number (S:P) ratio was made for each animal. Pig growth was divided into three approximately linear phases: birth to 6 kg, 6 to 25 kg, and 25 kg to slaughter weight. Average daily gain in the first two phases was correlated with birth weight (r = .3614, P < .05 and r = .5873, P < .001, respectively) but was not correlated with total muscle fiber number. In the third growth phase ADG was correlated with muscle fiber number (r = .4149, P < .001) and was not correlated with birth weight. The gain:feed ratio was also calculated for each pig during the third growth phase and was found to be correlated with fiber number (r = .4191, P < .001). These results suggest that muscle fiber number is an important determinant of postnatal growth such that pig littermates with a high fiber number tend to grow faster and more efficiently than littermates with a lower fiber number.
Dwyer
C M
CM
Department of Veterinary Basic Sciences, Royal Veterinary College, London, U.K.
Fletcher
J M
JM
Stickland
N C
NC
D000818:Animals; D000831:Animals, Newborn / Q000254:growth & development; D001724:Birth Weight; D006651:Histocytochemistry; D024510:Muscle Development; D009132:Muscles / Q000033:anatomy & histology; D013552:Swine / Q000254:growth & development*; D014886:Weaning; D015430:Weight Gain