SheepGenomics Muscle Sub-Program Training and Consultancy

Summary

This consultancy was conducted to assist with development of phenotyping methods and provision of phenotypic data for muscles from sheep within the SheepGENOMICS Muscle Sub-program. Specifically the following was achieved: 

On-site training was provided to Dr Jason White (University of Melbourne) and Victorian Department of Primary Industries technical staff in sheep muscle preparation and freezing technique for use in immunohistological and histochemical staining and in situ hybridisation. 

On-going discussions were held with Dr Jason White regarding appropriate sheep myofibre classification techniques and provision of protocols for staining and classification of myofibres. 

Muscle samples were prepared and provided to Dr James Kijas (CSIRO Livestock Industries) for genotyping, and data provided from Carwell sheep experiment conducted by Victorian Department of Primary Industries at Rutherglen. 

Callipyge and resource flock myofibre characterisation and morphometric measurements were provided to Dr Jason White for the phenotyping unit. 



Results for Callipyge and non-Callipyge genotypes showed there is a marked increase in the proportion of the total myofibre area comprising type 2X and a marked reduction in type 1, 2C, 2A and 2AX myofibres in affected (hypertrophied) muscles (semimembranosus and semitendinosus) of Callipyge compared to normal sheep, and little if any change in myofibre characteristics in non-hypertrophied muscles. Furthermore, the extent to which the percentage and size (cross-sectional area) of specific myofibre types is altered differs between affected muscles in Callipyge sheep. 
Results for samples from myostatin-mutant heterozygous and myostatin normal genotypes showed that cross-sectional areas of the more glycolytic myofibre types tended to be greater in the heterozygote compared to the normal animals. This resulted in an overall tendency for the myostatin-mutant heterozygotes to have myofibres with greater cross-sectional area than the normal myostatin sheep. There were no other significant effects of myostatin genotype on percent, cross-sectional area or relative area (percent of total myofibre area) of the myofibre types classified based on MHC characteristics.  
Dr Greenwood attended various SheepGenomics planning, progress and Annual Scientific Meetings. This work has helped to enable the successful conduct of muscle phenotyping within the SheepGENOMICS Muscle Sub-Program. The methodologies employed in this contract should continue to be utilised in conjunction with metabolic indicators of muscle characteristics to enhance capacity for prediction of favourable and adverse outcomes of genetic selection using gene markers for commercially important production traits. This work will benefit industry by enhancing understanding of relationships between sheep genotypes and phenotypes. More specifically, it will enhance the capacity for prediction of favourable and adverse outcomes of genetic selection using gene markers for commercially important production traits.