The main body of this work contributes to an understanding of the development and
growth of skeletal muscle in a range of Vertebrates from fish to pigs. Particular
emphasis is paid to the contribution of numbers and types of muscle fibres to
overall muscle growth and ultimate mass, and also to the mechanisms whereby
factors such as nutrition in mammals and temperature in fish may affect these
parameters. The work is divided into three main sections.
The first section covers aspects of prenatal mammalian development including
myogenesis and placentation. Muscle develops as two populations of muscle fibres.
Primary myofibres form first and this is followed by the formation of a larger
population of secondary fibres. Restricting maternal nutrition may compromise the
formation of secondary fibres but not primaries. Studies on the placenta and on
levels of specific factors, e.g. insulin-like growth factors, has given some insight
into the mechanism of nutritional effects on muscle fibre development. Nutritional
experiments have highlighted energy levels in the earlier stages of gestation as most
critical in the development of muscle fibre number. This finding has been
developed in pig experiments which have shown that extra feed in early gestation
can produce piglets with more secondary fibres at birth and which grow faster and
more efficiently to slaughter.
The second section incorporates work on postnatal mammalian muscle. Studies, on
pigs in particular, have shown that primary fibre number relates more to genotype
than does secondary fibre number. Total muscle fibre number correlates with some
parameters of carcass leanness and with postnatal growth rate and feed conversion
efficiency. The influence of factors such as nutrition, dwarfism, obesity and sex on
aspects of muscle growth and muscle fibre types has been studied as well as the
functional adaptation of muscle metabolism in different species.
The third section includes work on fish muscle development and growth in a range
of species. There is particular emphasis on the role of temperature during
embryonic stages on the development of muscle cellularity. In salmonid species
higher temperatures have been shown to produce muscle with larger but fewer
muscle fibres than at lower temperatures. There are also effects on the expression
of specific genes during development. The effect on muscle cellularity may have a
consequence for the posthatch growth of the fish when subsequently reared at the
same temperature. Further work has suggested that oxygen availability may be
compromised at the higher temperature and may be a significant factor in the
temperature affect on muscle cellularity. Temperature effects on muscle
metabolism have also been demonstrated.