The growth and differentiation of porcine skeletal muscle fibre types and the influence of birthweight
Handel, S.E.; Stickland, N.C.
Journal of Anatomy 152: 107-119
1987
ISSN/ISBN: 0021-8782 PMID: 2958439 Document Number: 299881
Muscle growth and development was studied in 49 Large White pigs from a total of 17 litters. Representative large (mean birthweight of 1544 g), small (1144 g) and runt (776 g) littermates were selected and slaughtered at the same age, ages ranging from birth to 128 days. Fresh frozen, serial transverse sections taken from the semitendinosus and trapezius muscles of these animals were stained for the histochemical demonstration of acid and alkaline preincubated adenosine triphosphatase, succinate dehydrogenase and glycogen phosphorylase. Profiles of the muscle fibre types were compiled for each animal. In both muscles the number of slow oxidative (SO) fibres, which were arranged together in groups within 'metabolic bundles', increased with growth. The transverse sectional area (TSA) of the semitendinosus muscle increased with the 2/3 power of liveweight whereas the area occupied by SO fibres increased at a rate significantly greater than 1.0 (P < 0.01). Regression analysis revealed that the area of this muscle occupied by SO fibers was greater (P < 0.001) in runt and small littermates relative to their large littermates when they were compared at an equal liveweight. This greater TSA of semitendinosus muscle classified as 'SO' in lower birthweight pigs was instigated through a combination of higher (P < 0.05) percentages of SO fibres and significantly greater (P < 0.001) SO fibre mean TSAs. The mean TSAs of all myofibre types from both muscles were similar between littermates of the same age but most types were of greater TSA in the lower birthweight littermates when compared (by regression analysis) at the same liveweight suggesting that fibre TSA was age rather than weight related. The higher percentage of SO fibres in the muscles of low birthweight pigs, when compared at an equivalent liveweight to their large littermates, appeared to be related to their affected secondary/ primary fibre number ratios which produced comparatively reduced numbers of fibres per metabolic bundle. This phenomenon, plus data on the mean number of slow fibres per metabolic bundle, indicated that it was apparently the number of slow fibres per metabolic bundle which was regulated with liveweight gain rather than the resultant percentage of slow fibres within the muscle.