The breeding direction at Richmond follows the SRS ( soft rolling skin ) principles which is a breeding system developed by Dr Jim Watts based on Moore’s pre-papilla cell hypothesis of follicle formation and fibre growth. The system is based on the conclusion that the skin of a sheep that is loose and thin ( as opposed to the industry preferred thick skins ) is biologically more likely to produce higher follicle densities of finer , superior processing and longer fibres. Watts was then able to identify the fleece characteristics that were associated with these sheep and implement new visual selection markers and measurement systems that could be used to extrapolate the numbers of these animals within merino flocks.
THE SCIENCE BEHIND FOLLICLE DEVELOPMENT
There are three types of wool follicles in the skin of a sheep: primary follicles which appear at about 65 days in the developing foetus; secondary follicles which appear at about 85 days; and secondary derived follicles which branch off the original secondary follicles at about day 105. These wool follicles are arranged in’ follicle groups’ which can vary in size and shape between animals. Each group consists of 3 primaries which have sweat glands attached to them and a genetically pre-determined number of secondary originals usually numbering around 15 per group and varying slightly depending on the animal. The secondary derived follicles vary greatly between animals and may number over 100 per follicle group. It is usually the number of secondary derived follicles that create the greatest difference in density between animals and if the animal has a high number of these then the fibres are finer and more aligned creating a higher quality fleece.
In the foetus prior to follicle development the dermis of the skin is mainly compiled of cells called fibroblasts. Fibroblasts produce collagen which is the main connective tissue component of the skin and is secreted into the dermis to form fibrils. It is these collagen fibrils that intermesh and form skin wrinkles. Some of these fibroblasts however change into pre-papilla cells which then group together to form wool follicles. If a large proportion of fibroblasts turn into pre-papilla cells then there is the opportunity for many wool follicles to be formed which will happen provided they are distributed frugally. The key to this process lies in the genetically pre-determined ability of the sheep to allocate only a limited number of cells to the development of the primary fibres. This leaves many cells for secondary and eventually secondary derived follicle development. Consequently if the genetic framework is right and providing there is a high number of starting cells the animal will produce a thin skin with high numbers of fine and highly aligned secondary and secondary derived fibres.
There are some important visual indicators that tell us when this biological process is in place. Firstly the traditional thick, locky staple is replaced by closely packed fibre bundles which are about the size of a matchstick. These bundles have a crimp that is much deeper and bolder than their micron would suggest. They are very well aligned with no cross fibres giving the fleece a floppy appearance often resulting in the wool falling over and opening up along the backline. The fibres are also extremely long as there is a strong correlation between thin skins and length of staple and conversely a negative correlation between fleece length and body wrinkle. And finally if inspected off shears the sheep is plain bodied and completely wrinkle free with a loose and supple pelt that can be easily lifted and stretched away from the animal. It is important to remember that high fleece weights on wrinkly sheep are simply caused by the extra skin creating a larger surface area to grow wool. Breeding wrinkles on sheep is a very dangerous shortcut to increasing fleece weight. It brings with it a multitude of problems such as fleece rot, low fertility and poor constitution as well as the gradual deterioration of fleece quality as the primary fibres increase in size and the animal slowly regresses towards its primitive two coated ancestor.
At Richmond we firmly believe that the biology behind the SRS system and the manipulation of major gene functions such as those that control lower primary fibre diameter will deliver us increasing levels of follicle density with a fibre that will be superior in quality to anything the industry has produced to date on an animal that is fertile, robust and sustainable.