New Generation Merino Sheep

Key Points

The science of sheep genetics and the development of sheep breeding values (ASBVs), performance testing, data recording and analysis have made huge advances over the last 25 years.

The result is that it is now possible to breed a ‘plain bodied’ merino sheep which is highly productive and because it has a significantly reduced risk of fly strike they do not require mulesing.

There are now approximately 4,000 farmers running ‘plain bodied’ merinos.


In Australia, Merino sheep are subject to the risk of being “struck” by blowflies which deposit their larvae in warm damp areas of wool and skin. The maggots which develop from larvae then proceed to eat the flesh of the sheep and will, if not treated, ultimately bring about the death of the sheep.

Definition: Mulesing is a word used to describe the surgical removal of loose folds of skin from the breach area of merino sheep. The operation is usually performed when the sheep are very young.


The practice of removing skin from the breech area of sheep as a solution to blowfly strike was first initiated by John Mules in the 1930s and has been used as a remedial solution to the problem of fly strike ever since. Over time mulesing became accepted as standard practice.

Sheep are frequently struck in the breach area because of the wool in that area becoming damp, and attractive to flies because of urine and faeces being caught on the wool. However, sheep can be ‘struck’ anywhere on the body if the wool is warm and damp.

Sheep that are wrinkly are more likely to get struck than ‘plain bodied’ sheep.

The pictures to the right are examples of how the adoption of different breeding principals have achieved a ‘plain bodied’ merino sheep which is far less susceptible to fly strike.

While there are now many ram breeders pursuing a plain bodied or dual purpose strategy, this is all as a result of the research work done by Dr Jim Watts some 15 years ago (then a CSIRO scientist).

Alternatives to surgical mulesing

The only long term, cost effective solution to the issue of mulesing is the development (breeding) of ‘plain bodied’ merinos which are generally more resistant to flystrike. These genetics are available and many ram breeders are using them.

There are also many tools available to assist ram breeders. Sheep Genetics,  a program jointly funded by Australian Wool Innovation and Meat & Livestock Australia, have developed many tools to assist breeders. An example of a scoring system is shown below.