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Variability of Fibre Characteristics within a Merino Wool clip

By Robert Pattison, Extension Specialist, Meat & Wool Innovation, Otago

To add value and improve the fibre characteristics of our Merino wool clip, it is important we understand the biological complexities of how the fibre grows. Only then can we make informed management and breeding decisions.

Key points

  • Fineness is the most important fibre characteristic of Merino wool and average fibre diameter accounts for approximately 75 per cent of the clean fleece value.
  • Up to 80 per cent of fibre diameter variability is due to variation between fibres within a staple and along individual fibres.
  • Fibre diameter is sensitive to changes in nutrition, particularly in the latter stages of pregnancy and during lactation.
  • Up to 80 per cent of fibre length variability is due to variation between fibres within a staple.
  • The environment and climate have the greatest overall effect on colour for a wool clip.
  • Approximately 80 per cent of genetic improvement in your future flock will come from the rams you use over your ewes.
  • Wool handling and classing will do very little to reduce the variations of fibre diameter, fibre length, fibre strength, colour or style within a wool clip.

Fibre diameter (fineness):

Fineness is the most important fibre characteristic of Merino wool. Average fibre diameter accounts for approximately 75 per cent of the clean fleece value.

The variation in fibre diameter within a wool clip is complex to say the least. The main sources of variation in fibre diameter come from:

  1. Differences between individual fibres within a single staple.
  2. Variations along the length of individual fibres.
    (1 and 2 account for approximately 80% of fibre diameter variability.)
  3. Variation between individual staples, approximately 4 per cent
  4. Differences between fleeces, approximately 16 per cent.

The wool follicles from which the fibres grow directly influence fibre fineness. There are three wool follicle types in the skin of Merino sheep:

  1. Primary follicles, which develop 60-70 days after conception
  2. Secondary follicles, which develop 120-130 days after conception
  3. Secondary derived follicles, which develop up to 70 days after birth.

Differences in fibre diameter between these follicle groups have the largest effect on fibre diameter variability within a mob, with secondary and secondary derived follicles accounting for approximately 90 per cent of the variation.

The other important factor affecting fineness is variability along the length of the fibre.

Fibre diameter is sensitive to changes in nutrition. Nutrition has a major effect on wool follicle development, particularly in the latter stages of pregnancy and during lactation.

The critical time for follicle growth and development is from 80 days after conception to 70 days after birth. Good feeding and nutrition during this period are essential to ensure maximum follicle development and low fibre diameter variability.

If Merino farmers get it wrong during this period, it has a very significant impact on the animal’s lifetime wool production, and fibre diameter variability within the fleece.

If secondary and secondary derived follicles get plenty of nutrients from the blood supply during their development, their numbers will be maximised. The average fibre diameter will be finer than in a fleece from an animal that was deprived of nutrients during this critical period.

Fibre Length

Fibre length and staple length are closely correlated. Fibre length variability occurs between fibres, between staples and between fleeces.

Up to 80 per cent of fibre length variability is due to variation between fibres within a staple. Only around 10 per cent of length variability is due to variation between staples within a fleece.

The greatest variation in fibre length is in the secondary and secondary derived follicles, because these make up the largest percentage of the fibre population.

The fibres from the secondary derived follicles develop much later (up to 70 days after birth), are much shorter and finer due to the competition they face from the secondary fibres.

The remaining 10 per cent of length variability is due to variation between fleeces within a mob. This means that sorting individual fleeces based on their average length will only reduce total fibre length variation within a mob by approximately 10 per cent.

Colour

The environment and climate have the greatest overall effect on colour for a wool clip. Other factors such as breed-type, feeding, flock management, animal health and control of external parasites also effect colour of individual fleeces within a flock. There are two types of colour:

  1. Brightness – how white the wool is
  2. Yellowness – how creamy or yellow the wool will is.

High rainfall with warm humid temperatures causes canary yellow, green, blue and brown bacterial stains to develop. Low rainfall and low humidity levels result in good colour white wool.

As a result, Merino flocks in Central Otago tend to produce bright white wool, whereas Merino wool clips from the North Island generally have greater degrees of yellowing.

Style Grade

The style of a wool clip is affected by a combination of factors:

  1. Flock environment
  2. Climate and weather
  3. Management and feeding
  4. Breeding
  5. Wool handling, classing and packaging.

The environment where sheep live will have a major effect on the amount of contamination from moit and seed, or dust and dirt that can penetrate into the fleeces. As mentioned above, climate has a major effect on wool colour and soundness. Drought conditions also cause a loss of strength (tenderness) in the fibre.

Management and Feeding

As discussed earlier, if farmers get their management wrong when their ewe flock is halfway through pregnancy or during the lactation period, then the variability of fibre diameter and fibre length within their next generation will be severely affected.

If the flock is stressed due to internal or external parasite infestation, fly strike, footrot, sudden changes of diet or feed shortages, this can affect fibre strength creating a tender wool clip.

Winter feeding can also affect style. Feeding out hay and silage can contaminate back wool in the fleece with moit, or sheep may get mud contamination in their fleeces when fed on winter crops such as turnips or swedes.

Shearing time and frequency affects staple length, soundness and colour:

  1. Pre-lamb shorn wool has high tensile fibre strength and very good colour.
  2. Post-lamb shorn wool can have lower tensile strength and greater degrees of yellowness.

Crutching and dagging reduce the chances of urine or dung stain contaminating your wool clip.

Breeding

Selecting sheep with fleeces of good character and style is important so the fleeces can survive the challenges from the environment in which the sheep live. This means selecting for fleeces with clearly defined staple formation and thickness, and a well defined even crimp from the tip to base of the staple. Tips of staples should be blunt rather than pointed.

By selecting sheep with fleeces of good style and character, you will reduce the amount of dust and vegetable matter contamination penetrating into the fleece. Good character fleeces will shed water and will be less prone to discolouration and fly strike.

It is important to cull sheep with the following wool faults:

  1. Fleeces that have poorly defined crimp and plain staples that are mushy or excessively tippy.
  2. Sheep showing any signs or evidence of black or pigmented fibre.
  3. Sheep showing hairy britch on the rump or hind legs.
  4. Sheep with fleeces that are subject to yellow discolouration.

Remember, the rams you use over your ewes have the greatest influence on your future flock. Approximately 80 per cent of genetic improvement will come from them. You must take care when selecting them to avoid the faults mentioned above, particularly black fibre, hairy britch and yellow discolouration.

Wool handling and Classing (Quality Control)

Wool handling and classing will do very little to reduce the variations of fibre diameter, fibre length, fibre strength, colour or style within a wool clip.

The purpose of skirting is to minimise the extreme variations of style and staple length within individual fleeces by removing faults, which would otherwise downgrade the overall value of a line of greasy wool.

The purpose of classing is to group fleeces of similar style, fineness, staple length, soundness and colour into lines for sale to a buyer. In doing this, the classer has less than 20 per cent of the total fibre diameter variability between fleeces within a mob to work with.

Achieving consistency of fibre length within a line of fleece wool is even more difficult, in that the classer has only 10 per cent of fibre length variability between fleeces within a mob to work with.

 

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