Penrhyn farm - Project Introduction
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 nine known mutations of the Myostatin gene in cattle, some of which are breed specific and others which affect more than one breed. There are three main mutations that occur within all Limousin populations (as well as other breeds) as follows:
Variant F94L
F94L increases the size of muscle fibres with no associated increased in calving difficulty, lowered fertility or longevity, and by far the majority of animals in the breed carry this gene. Homozygous animals (two copies of 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 higher proportions of polyunsaturated fats. Heterozygous animals (only one copy of the gene) also exhibit these characteristics but not to the same degree. As a result of the high frequency of this gene in the Limousin population, most animals have double copies and exhibit its characteristics; increased muscle mass without increased calving difficulties, lowered fertility or longevity. It is therefore partly responsible for the breed as it is today and one of the reasons behind its commercial success.
Variant nt821
This variant is recessive and is carried by a lower proportion of animals in the breed. Animals that are homozygous recessive will exhibit characteristics of the condition: larger loin depths, reduced fat depths and large, rounded rump and thighs. However, unlike F94L, homozygous animals (i.e. those with two copies of the gene) may also have slightly heavier birth weights bringing with it the potential for more difficult calvings. If animals are heterozygous with F94L (i.e. F94L/nt821) they will still exhibit quality carcase characteristics but are less likely to be affected by more difficult calvings. These animals are known as ‘carriers’.
Variant Q204X
This is a ‘partially dominant’ mutation of the Myostatin gene and, as with nt821, it is carried by a small proportion of animals. Animals that are homozygous (two copies of the Q204X gene) will exhibit characteristics of larger loin depth, reduced fat cover and greater meat tenderness. However, they may also have the potential to exhibit larger birth weight and, if females, slightly reduced milking ability. Animals that are heterozygous with F94L (ie F94L/Q204X) – also known as ‘carriers’ - will still exhibit quality carcase characteristics but are less likely to be affected by larger birth weights and reduced milking ability.
Two further variants of Myostatin exist but are relatively rare in their occurrence. Known as nt419 and E291X, their effects in homozygous and heterozygous states are similar to nt821 and Q204X respectively.
What will be done:
60 younger breeding cows and heifers (eligible as replacements) plus the 3 Limousin stock bulls will be DNA tested in order to determine what combination of Myostatin variants they carry. Individual animal DNA sample packs will be supplied and 20-40 hairs will be plucked from the switch of the tail for every animal, complete with good hair follicles, and placed in the sample bags with animal identity details recorded on the bag. After posting to the Limousin Cattle Society, samples will then be forwarded to Weatherbys Ireland for DNA testing, which will determine the Myostatin variants carried.
The DNA samples will also be included in the following BLUP run for the Limousin breed and compared against the SNP key for the breed to produce genomic breeding values for carcase and maternal traits as follows:
Carcase weight kg
Slaughter age days
Fillet kg
Striploin kg
Topside kg
Rump kg
Silverside kg
Knuckle kg
Retail Value £
Age at first calving
Longevity
Calving Interval
Calf survival
All of the above will be shown as bar charts benchmarked against Limousin breed percentiles for every animal. As long as the animal is at least 50% Limousin (there is some Belgian Blue blood in the herd), comparison with the Limousin SNP key is valid.
Heifers chosen as potential breeding heifer replacements will undergo pelvic measurements which will provide important information on their individual ability to avoid calving difficulties.