AUSTRALIAN LIMOUSIN BREEDERS SINGLE GENES

ED/ED: Homozygous dominant black

ED/e: Dominant black/recessive red

ED/ E+: Dominant black/wild type

E+/e: Wild type/recessive red

E+/ E+: Homozygous wild type e/e: Homozygous recessive red

Protoporphyria

Protoporphyria is due to the presence of a defective gene that is normally responsible for the formation of the enzyme ferrochelatase which is involved in the combination of iron and protoporphyrins to form haem, a component of haemoglobin.

If two defective genes are present (homozygous defective) then the animal is likely to exhibit the symptoms of protoporphyria (photosensitisation).

If one defective gene is present (heterozygous) the animal will be a carrier but is very unlikely to suffer from photosensitisation.

If both genes are normal (homozygous normal) the animal will be normal.

The various mating combinations portrayed for the polled gene are identical for black colour.

A DNA test is available in Australia to test for those animals which appear normal but carry a defective gene. These are known as protoporphyria carriers.

PR

– Free Proto Normal (PN)

PR – Carrier The animal is a carrier of the abnormal gene for protoporphyria (PC)

Protoporphyria Status will be indicated as:

Proto normal

Proto free by pedigree

Proto carrier

Proto suspect (parent of diseased animal)

Proto status unknown

(No longer a suffix, can be found on the animal information page)

Myostatin F94L

A normally functioning myostatin gene inhibits muscle growth. The mutation known as F94L which has a high frequency in the Limousin breed is one of three missence mutations which does not cause a loss of function of the myostatin gene. It appears not to cause an increase in the size of the muscle fibres but does cause an increase in the number of muscle fibres. It is not associated with high levels of calving difficulty or lowered fertility and longevity.

The loss of function myostatin mutations are associated with high levels of calving difficulty and lowered fertility and longevity.

Most Limousin bulls carry two copies of the Limousin muscling gene so each of the progeny will get one copy of the Limousin muscling gene. Animals with one copy of the gene are likely to exhibit about half the differences shown above. A Limousin cross calf is expected to have about 9.5% more silverside, 9.5% more eye muscle area 4% more retail beef yield, with a 3% increase in tenderness of the loin muscle and 5.5% more tender silverside.