Myostatin and Murray Greys 

The MH gene is present in all mammals and is responsible for regulating muscle development through the production of a protein called myostatin. In cattle, natural mutations can lead to the deletion of myostatin, resulting in a double muscled phenotype.

While double muscled cattle have higher muscle mass and kill out percentages, they also have lower fat and bone mass, and smaller internal organs. The myostatin gene has both non-disruptive and disruptive variants.

Non-disruptive variants such as F94L (common in Limousins), S105C, and D182N, can increase muscle size without causing fertility, longevity, or calving issues.

Disruptive variants, on the other hand, heavily influence muscle development and has been said to cause calving difficulty, lower fertility, milkability, shorter longevity, and leaner carcass. Disruptive variants include NT821, which is common in Belgian Blue and Partenaise breeds, and Q204X which is common in Charolais.

While cattle with one copy of the gene typically do not always show noticeable effects, mating two animals with one copy can result in progeny with two copies of the gene, exhibiting extreme effects.

Murray Greys can carry the disruptive variant, NT821. We have found the effects of the variant can be present in single carrier animals. We have never knowingly encountered a Murray Grey with two copies of the gene mutation, but have a couple single carriers that have posed no issue.

At this time we are still determining our independent opinion on single carriers of myostatin, and do recognize it as a breed trait present in many of the founding genetics of the breed. In a recent study published by the Murray Grey Society in Australia, it has been found that over 20% of Murray Greys carry a copy of Myostatin. Single carrier females are attractive, smooth muscled, easy fleshing females with efficient feed ratios and don’t typically display the bubble butt look associated with double muscling. None of our carriers have experienced calving complications when bred to a non carrier bull, and they are typically considered “do-gooders” on range or times of poor forage. In 2023, we experienced significantly more gain in calves that either carried a single copy, or that were raised by females with a single copy. We have found that carrier bulls can at times produce an inconsistent calf crop depending on if they pass their mutation to their calves. We have seen a reduction in marbling on single carrier carcasses, but higher dress out yields.

At this time we test all calves for myostatin that are not clear by inheritance, and will not sell a known NT821 carrier without disclosure. We want to assure our customers peace of mind and transparency for them to make their own opinion on the condition and sound breeding decisions. We speak to many breeders who have never tested their herd, but believe they do not have any carriers. Carriers are often times unidentifiable by visual inspection, and it can be safely assumed that most untested herds do in fact have carrier animals. It is easy to inadvertently select carrier animals as replacements as they typically grow better, have higher daily gains, and more natural muscling.