Catch-up growth in pigs: a relationship with muscle cellularity

Abstract

ABSTRACTAn investigation was made into a possible relationship between the relative growth potential and skeletal muscle fibre number in low birth weight Large White pigs and their heaviest birth-weight littermates. Estimates of the total fibre number of m. semitendinosus were made from 23 pairs of ‘small’ and ‘large’ littermates. Littermates were slaughtered at the same age and were of a mean live weight 86 (s.d. 15) kg. Small littermates (mean birth weight 939 (s.d. 164) g) had, on average, lower live weights at slaughter (P < 0·001) and lower muscle fibre numbers (P < 0·05) than their large littermates (mean birth weight 2085 (s.d. 343) g). However, pigs within the low birth-weight category exhibited various degrees of catch-up growth with their heaviest littermates and some individuals actually exceeded their large littermates in live weight at slaughter. The relative live weights at slaughter and relative muscle fibre numbers of small and large littermates were determined by expressing the value for the small littermate as a proportion of the corresponding value for its large littermate. No correlation existed between relative live weight at slaughter and relative muscle fibre number of small and large littermates. The small littermates were then divided into two groups by their mean value of relative small to large slaughter weight (0·84). The littermates of low relative slaughter weight (≤0·84) exhibited a large range of muscle fibre numbers although their mean fibre numbers were lower than their large littermates (P < 0·05). This large range was probably responsible for the lack of correlation mentioned above. Those small littermates which exhibited a good degree of catch-up growth (relative slaughter weight >0·84) possessed fibre numbers which were not significantly different from those of their large littermates. These results suggest that pigs which exhibit an appreciable degree of catch-up growth always contain high relative numbers of fibres in their muscles. Those which show a poor degree of catch-up growth (≤O·84) exhibit a range of fibre numbers because there may be environmental and other factors which prevent some pigs from realizing their full growth potential. The results of the present study advocate muscle fibre number as an indicator at birth of potential for post-natal growth performance.