Myostatin (Double Muscling)

Myostatin is found in all mammals and influences the protein that controls muscle development. Natural mutations of the gene produce proteins that are less effective at controlling muscle development, and often results in increased muscle mass (Double Muscling). Despite the name, double muscling has no association with the duplication of muscles, but rather an increase in the number of muscle fibres, and fibre enlargement (hypertrophy), with double muscled animals having nearly twice the number of muscle fibres. Myostatin genes are inherited in a simple recessive manner where homozygous recessive animals are affected. However, for some of the mutations, heterozygotes can also express double muscling in the phenotype, although usually to a lesser degree than affected homozygous recessive animals. There are 9 known variants of double muscling (C313Y, D182N, E226X, E291X, F94L, Nt419, Nt821, Q204X, S105C). Three of these are more commonly found than the others – they are: F94L, Q204X and Nt821. Some of the most prominent effects of myostatin (depending on which variants are present), are:

• Prominent creases between muscle groups
• Minimal fat cover and modified fat composition
• Shorter, thinner and less dense bones
• Delays in puberty, reduced milk production (likely due to lack of fat deposition)
• Increased likelihood of dystocia
• Enlarged tongues in new-born calves
• Poorly developed genitals
• Increased susceptibility to respiratory disease and heat stress probably due to increased demands on aerobic and metabolic activity
• Lower intramuscular fat content, poorer meat flavour profile
• Increased meat tenderness and yield

SNP Test results are presented as having copies present (0), having one copy (1) or two copies (2). The results of mating’s between sires and dams who do, and do not have a mutation can be grouped as follows: