Knowing the myostatin status of your animals, will help you to select bulls with the most appropriate myostatin traits for your breeding program. This will lead to better calving ease and help with the ever-present trend to improve carcass confirmation and quality.
There are both advantages and disadvantages of breeding with animals carrying the myostatin gene, which is why it is imperative that you know the carrier status of your breeding animals.
What is Myostatin?
Myostatin is a gene that influences the production of proteins which control muscle development. When an animal is identified as having one of the mutations it means that they have inactive genes which do not control muscle growth as effectively, this can result in increased muscle mass, or “double muscling”.
Currently in cattle, there are 19 known mutations of the gene, some of these mutations are breed specific and within the British Charolais herd book, two prevalent variants are found – F94L & Q204X.
Research conducted by Adelaide University in Australia concluded that the effect of the F94L mutation on birth and growth traits was not significant but was associated with an increase in meat weight and a reduction in fat depth. The results for the average effect of substituting a single copy of the variant F94L variant indicated an increase in silverside between 5.8 and 7.2% and meat weight of between 5.9 and 7.3%. There was also a reduction in P8 fat depth, intramuscular fat and carcass fat weight.
Calves used for this study, carrying 2 copies of the variant F94L marker, produced carcasses with approximately 12 to 15% more meat and 16 to 33% less fat compared with calves with no copies of the variant F94L allele, while single carriers produced approximately 3% more meat weight, while fat depth measured on live calves was 9.8% lower. Therefore, the F94L variant appears to have many positive effects without correlated negative effects of some other myostatin variants.
In a study published in the Oxford University Press Journal of Science on the effects of the Q204X gene in Charolais cattle, it was shown that the Q204X mutation leads to an increase in muscle mass. This creates a dramatic increase in saleable meat yield because of the improved dressing percentage, reduced carcass fatness, and fineness of the limb bones. In this study, animals with a single copy of a mutated allele were slightly heavier at birth.
These animals showed consistently greater carcass yields, the thighs were thicker, and the rib eye areas were larger. They were also markedly leaner, with less internal fat and less fat on the 6th rib. Therefore, the presence of even one copy of Q204X was shown to increase the beef value of these animals drastically. Regarding meat quality, trained taste panellists indicated that the meat of young heterozygous bulls was more tender. This better tenderness can be a consequence of a reduced collagen content and a smaller mean area of the muscle fibre section because both characteristics have been shown to be related to muscle tenderness.
How are these genes inherited?
All reproducing species have two copies of each gene – called alleles. If your Charolais has one copy of the myostatin variant (one allele) it is classed at heterozygous, if it has two copies (two allele) it is classed as homozygous.
The table below shows the chances of inheriting depending on the status of the parents:
The information gained from knowing the myostatin status of an animal is helpful when making breeding decisions for your herd. However, it is just one tool which should be used in conjunction with the wider information available such as Estimated Breeding Values (EBV’s) – which predict the performance of the animal based on its back pedigree, accurate measurements and the performance of its herd mates – and your own judgement on type and pedigree.