Double muscling is a genetic disease characterised by enlarged skeletal musculature.
This feature of genetic modification, reported in Belgian Blue, Piemontese, Blonde d'Aguitaine and Devon breeds, is induced by modification of the myostatin gene (muscular hypertrophy gene), known to be associated with the double-muscling phenotype. This results in a disturbed metabolism of trans-18:1 and conjugated linoleic acids and muscle over-replication.
Clinically affected cattle have grossly enlarged musculature, with double-muscled cattle possessing nearly twice the number of muscle fibres at birth than normal cattle. Affected cattle also have reduced exercise and heat tolerance, delayed-onset puberty, reduced fertility due to an increased incidence of mortality in double-muscled embryos, increased incidence of dystocia, reduced milk production and increased calf mortality.
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