WHAT IS THE F94L GENE?
Myostatin (Double Muscling) in Limousin Cattle
Introduction
Myostatin - double muscling- in Limousin cattle is not a new phenomenon. Testing is becoming easily available as there are benefits for both the breeders and the purchasers.
For breeders - knowing the Myostatin status of animals within herds will be important for the choices and options it offers herd management and breeding programmes.
For purchasers - it will similarly allow choices to be made based on knowledge and understanding when buying Limousin cattle
Background
Most characteristics of cattle that we are familiar with such as growth, fertility, carcass traits, etc are controlled by many genes. A few characteristics are controlled by single pairs of genes. Coat colour and polledness are examples of this, as is double muscling.
Breeding and Single Trait Genes
When characteristics are controlled by single pairs of genes, the outcome of particular matings can be predicted once the status of both parents is known. Two main principles apply:
Dominance: Most single gene traits have dominant and recessive forms of the gene. The combination of these in the pair of genes carried by each animal often determines what the animal looks like. For example, the polled gene in Limousins is dominant and the horned gene is recessive. If the animal carries two horned genes (represented by pp) it will be horned. If it carries two polled genes (PP) it will be polled. If it carries one of each (Pp) it will be polled because the polled gene is dominant.
Hom - and Heterozygous: using the example above, animals carrying to polled genes (PP) or two horned genes (pp) are known as homozygous. If the genes are different (Pp) the animal is heterozygous.
What is Myostatin?
The Myostatin gene is found in all mammals and influences the production of a protein that controls muscle development. Natural mutations of the gene produce proteins that are less effective at controlling muscle development, which results in increased muscle mass. There are three main mutations that occur within all Limousin populations but we will focus on the F94L gene as it is most common.
Variant F94L
This is perhaps the most familiar variant to us due to the high levels of publicity it has received recently due to it's benefits. F94L increases the size of muscle fibers with no associated increased calving difficulty, lowered fertility or longevity and by far the majority of animals in the Limousin breed carry this gene. Homozygous animals (two copies of the f94L) show increases in primal cut weights by up to 19% and overall Retail Beef Yield by up to 8%, this also leads to better rates of feed conversion. Meat quality is also typically better with higher rates of tenderness, reduced fat and high
proportions of polyunsaturated fats. Heterozygous animals also exhibit these characteristics but not to the same degree. The variant F94L has been dubbed as the 'Profit Gene'.
Benefits of Myostatin
The presence of Myostatin mutations in the Limousin population have been and could continue to be advantageous for the breed in supplying the carcass attributes it is known for:
Meat Yield: The carcasses of double-muscled cattle dress out at between 65% and 70% due to a combination of increased muscle mass, reduced body fat, reduced bone mass and smaller internal organs. This is up to 19% higher than cattle that don't exhibit double muscling. When muscle weight gain per unit energy intake is taken into account, double-muscled cattle have better feed efficiency than normal cattle.
Meat Quality: Meat from double-muscled cattle tends to be of better quality due to a combination of increased tenderness, reduced fat content and a higher proportion of polyunsaturated fats.
Significance for producers: Double-muscled animals produce a higher proportion of desirable cuts of lean meat with great efficiency than do comparable, conventional cattle. The majority of animals carry the f94L mutation and exhibit all these characteristics without any detrimental effect on birth weight, calving ease, fertility, longevity and milk.
Significance for consumers: This meat is more tender, and being lean and having a higher polyunstaturated fat content, conforms more closely with current nutritional guidelines than meat from normal animals.
Disadvantages of Myostatin
On a population level, because of the high frequency of f94L, there are no significant disadvantages to these mutations.