Breeding For Better Fleece©
By Linda Wendelboe, November 10, 2005
(Click for Printable Version)

Introduction

This article deals with fleece traits that can be selected for improvement through breeding as well as  tools that can be used to select superior animals for such a breeding program.  It is focused primarily on wool production, but keep in mind that good conformation plays a big role in easy animal husbandry.  For that reason, Shetland breeders should place a great deal of emphasis on  sound conformation as well as on wool production.

Traits that are highly heritable respond well to breeder selection for improvement.  This means that choosing animals that are superior for these traits for breeding should result in improved progeny and in an improvement in the flock over time.  The heritability of a number of conformation and fibre traits in sheep seems to be moderate to high. Research and measurement of fleece production and heritability in Shetlands is very meager so work done with other fleece-type sheep and goats such as merino and cashmere is referred to.

There is a range in the length and style of fleece found in Shetland sheep.  Sometimes the range is subdivided into three smaller ranges:  primitive (long staple (6" +), straight or wavy, distinct double coat, Icelandic fleece type), classic (moderate staple length (4" - 5"), crimpy, feathered lock structure) and improved (shorter staple ( less than 3"), tight crimp and blockier lock structure).  Whatever length and style of fleece is chosen as your goal, it should still conform to the breed standard if breeding for registered stock.  The extremes should not be registered when they do not fit within the breed standard.  See Breed Standard  and Fleece Characteristics.

What fleece traits should I select for improvement?

Select those traits for improvement that make sense in your situation.

Quantity and quality are the most important factors in fibre production, just as they are in milk or meat production.  Therefore, it makes sense to select traits that will improve the quantity and quality of fleece from your flock, in accordance with proper Shetland fleece style.  Keep in mind that Shetlands should also be selected on appropriate reproductive traits such as ease of birth, mothering ability and milk production.  In the show ring, proper conformation, Shetland type and presence are also rewarded.  These traits can add significantly to the sale prospects of an animal or its progeny in addition to the value based on its fleece.

Most Shetland wool now produced and sold in North America goes into niche markets. Markets in different locations may place different values on various wool characteristics.  In general however, purchasers of wool rate the following fleece characteristics as important and pay a premium for or do not discount for wool that has:

Fineness
Uniformity within the staple
Lack of medulated fibre (no straighter, hairier type fibres mixed with the wool)

Appropriate staple length

Soundness/strength

High percentage clean yield

Fineness is measured in microns and usually has the largest impact on the price paid for wool. The finer the wool, the higher the price.

Wool that is uniform spins easier and the end product has a better feel or "hand".   There is usually a range of both fibre diameter and fibre length that will give the best results.  For instance, wool having fibres with a variation in diameter of 4 or 5 microns will be easier to spin than wool containing fibres that vary by 10 microns or more.  Handspinners may be able to deal with more variation than commercial mills.  In the spinning process, the speed of spinning tends to throw the coarser fibres to the outside of the yarn.  The faster the yarn is spun, the more this tendency is accentuated.  If the wool is made up of a mix of coarse and fine fibres, the resulting yarn will feel more like the coarse fibres than the fine ones.

Medulated fibres (straight, more hair like) are hollow and lack crimp. They have different spinning characteristics than wool, are often of a higher diameter than the wool and take dye differently as well.   These can be removed by hand or through a commercial “dehairing” process. The hand process is time consuming, the commercial process is expensive and both result in a higher processing loss.

Clean yield is important to purchasers as most fleece is paid for on a raw, unwashed weight basis. If the clean yield percentage is high after washing or scouring, the purchaser gets more usable wool for their money.

Staple length will determine the type of spinning method used and the end products that can be made from the wool.  Many mills have a strict range of tolerance and can only spin wool with a staple that falls within their range.  Handspinners tend to have fewer restrictions but are usually sensitive to matching staple length with desired end product.

Wool that has a stress break or is weak or tender due to heredity, the animal's poor health, improper feeding or some other cause will be discounted.  It does not spin well and the resulting end products will be of a lesser quality.  This will be of concern to handspinners and commercial purchasers alike.

Density is not of interest to purchasers but does factor into a breeder's economics. One Shetland that has an annual sheared usable wool weight of 4 pounds will have a better rate of return than one with an annual sheared usable wool weight of 3 pounds, all other things being equal.

Crimp is also not ranked highly by commercial purchasers; it may be of more interest to handspinners. However, crimp may be an indicator of fineness and density and, as such, it is of direct interest to the breeder. Also, crimp can impart elasticity and loft to yarns and therefore is important for garment manufacturing.

Colour is not formally ranked but may have distinct economic ramifications as well. Commercial purchasers have historically preferred white or light wool as it can easily be dyed any colour. Uniformity of colour may also be of value to those purchasers as dark fibres in a predominantly light fleece may not be acceptable, depending on the process to be used. However, handspinner and other niche markets often pay a premium for natural colours, following fashion trends.  For information on colour genetics see Colour .

“Hand" or "handle" may best be described as the way the wool feels. It is a combination of the softness, fineness, uniformity, lack of medulation and other more subtle characteristics. Wool with a good "hand" will be easier to sell into a premium handspinners market and will product a superior feel in the garments or other products made from it.

While any number of the traits listed above could be selected for improvement, keep in mind that the more traits selected for improvement, the smaller the gain will likely be for each trait.  Selecting to improve one or two traits will yield faster progress on those traits.  Also, there are situations where progress on one trait may be linked to a change in performance in another trait.  For instance, as fibre diameter decreases, staple length also tends to decrease.  If you wish to keep a longer staple length and also to improve fineness, it will take very careful selection and more generations to accomplish. So keep it simple; perhaps chose to first improve those traits that suit your market for wool or the end use you intend for the wool.

Now that I have selected the traits that I want to improve, what’s the next step?

When you have chosen the traits you wish to improve, you then have to select breeding stock that will give you the best potential for that improvement.

Evaluate your ewe flock.  Measure the traits you wish to improve.  Review the average numbers for the flock for those traits.  Decide what your minimum standard will be to retain a ewe in this breeding program.  For instance, if a ewe is well below the flock average for the selected traits, consider removing her from the program.  Another method would be to aim to replace a certain percentage of the lowest performers as soon as superior ewe lambs are available.

Evaluate your rams and any rams to be bought in.  Again, measure the traits you wish to improve.  Most of the potential for improvement will come from using superior rams over the ewes that exceed your minimum standards. 
 

What methods can I use to evaluate and compare one animal to another?

If you are only selecting one trait to improve, comparing phenotypes is a good place to start.  The animal that has a better phenotype for that trait is probably the better animal for the breeding program.  However, when selecting for more than one trait, Breeding Values and Selection Scores are tools that can help. When possible, also evaluate the parents, siblings and progeny of the animal.  High performing animals from high performing families are the most desirable in this process.

Breeding Value in the main tool discussed here for selecting breeding stock.  Breeding Value relies in a significant way on the estimated heritability of the traits to be improved.

Estimated heritability, as it is used here, equals genetic variation divided by total variation.  Total variation is that caused by the environment plus that due to genetics.  If the role of the environment is small, estimated heritability increases, as does the potential for rapid improvement through selective breeding. If the effect of the environment is large in determining a phenotype, the ability to select the best breeding animals for improvement based on phenotype is reduced. Therefore, the rate of improvement will also be reduced.  There is technical research and a number of formulas that can be used to work out estimated heritability, but for our purposes, the following table will suffice.  The estimated heritability (denoted by “h^2”) of fleece traits in other sheep and goats generally falls in the high range. Shetland fleece traits likely have similar rates of heritability. 

Breeding Value (BV) for any particular trait can be expressed as:

BV = h² x (Phenotype of individual A - the average Phenotype of flock), where h² is the estimate of heritability.

Selection based on straight phenotypic comparisons may over or under rate the value of the animal for breeding purposes, as shown in the following example.
 

Estimated heritability of fleece weight is .6 for this example.

BV Fleece Weight, Ram A =.6 x (3.75 - 3.5) or .15

BV Fleece Weight, Ram B=.6 x (5.5-3.5) or 1.2

By direct comparison, Ram B is approximately 40% better in fleece weight production than Ram A. However, considering the high estimated heritability of fleece weight, Ram B is actually 8 times or 800% better in terms of his estimated ability to provide improvement in his progeny, in this example flock.

To calculate the BV for Average Fibre Diameter, the estimated heritability for this example is .5. In this case, a decrease in the micron is the objective so the calculation uses the average P (phenotype) of the flock minus the individual P (phenotype) for the trait:

BV Average Fibre Diameter, Ram A= .5 x (28-21)= 3.5

BV Average Fibre Diameter, Ram B = .5 x (28 - 25) = 1.5

Again, direct comparison of phenotype shows that Ram A is 20% finer than Ram B, but from a breeding point of view, Ram A is more than twice as valuable for improving fineness in this example flock.
 

To find the Breeding Value for a specific trait of either Ram for a different flock, the average phenotype value for that trait for that flock has to be used in the calculations.

Multiple Trait Selection

If a breeder is only selecting for improvement of one trait, selecting the breeding animals based on best phenotype will provide an improvement in progeny, so long as the environmental effect is low. However, if a number of traits are selected for improvement at the same time, developing and using a Selection Index will best assess the overall merit of one animal compared to another animal.

A Selection Index uses a calculation, the Selection Score, to rank animals from best to worst, based on the breeding objectives selected. The highest scoring animals will be the best choices for overall improvement. The breeder must choose the traits to include in the program carefully. Selecting too many traits at once can result in less progress than hoped for.

The selected traits are given weighting factors, with the most important trait given the highest weighting. Importance and weighting may be based solely on expected economic return or can include other factors; it is up to the individual breeder to decide. The weighting process should also consider trait correlations. For example, in sheep: A decrease in fibre diameter (good) often accompanies an increase in density (good) but an overall decrease in fleece weight (bad); an increase in staple length (good) often accompanies an increase in fleece weight (good) and an increase in fibre diameter (bad).

Breeders should set an independent cut-off level for each trait selected. Animals that do not meet that level for each trait should not be used in the improvement program.

The Selection Score for an animal is calculated as follows:  (BV Trait 1 x Weighting Factor Trait 1) + (BV Trait 2 x Weighting Factor Trait 2) + BV Trait 3 x Weighting Factor Trait 3) etc. There are other formulas that can be used to refine the results but will not be dealt with here.

Selection Score Calculation Example:
 

The weighting factor for the average fibre diameter will be set highest as that is the trait determined to be most important for this example calculation.  It will be 3.

The weighting factor for fleece weight for this example calculation will be set at 2.

Selection Score for Ram C:  

Ram C Fleece Weight BV = .6 x (5 - 3.5)  or .9
Ram C Average Fleece Diameter BV = .5 x (28 - 23) or 2.5
 

(BV Fleece Weight x 2) + (BV Fibre Diameter x 3) = (.9x2)+(2.5x3) or 9.3

Selection Score for Ram B:

(BV Fleece Weight x 2) + (BV Fibre Diameter x 3) = (1.2 x 2)+(1.5 x 3) or 6.9

Ram C ranks more highly for these traits than does Ram B.  You might try to figure out the Selection Score for Ram A to see if you have the idea.  Try changing the weighting and redo the calculations for all rams to see how the ranking changes, based on weightings.


How can I tell if my breeding program is working? 
  
          Measuring the selected traits in the progeny is the best way to tell if you are making progress.

Most North American breeders fall into the small flock category (less than 25 breeding ewes). Progeny testing should be a key element to measuring the progress in breeding programs but obtaining sufficient sample size to make appropriate judgments can be difficult in the small flock situation.  Within flock measurement will be more meaningful than between flock measurements, unless the other flocks being measured choose to use the same standards. Flock management should be organized to optimize accurate, consistent measurement of the fleece traits to be improved.

Shearing should be done annually, with best measurements taken for a consistent period of fibre growth; (i.e., April one year to April the next year). All measurements must be carefully recorded.  All fleece from each Shetland should be weighed after shearing. Staple length should be measured with a ruler. Crimp frequency and amplitude can also be measured at the same time. A relative measurement for density can be taken by dividing fleece weight by staple length. The higher the resulting number, the more dense the animal.

Fineness and uniformity can be measured by taking fibre samples for histograms. Lustre and hand can be measured by comparison to reference benchmark samples collected by the breeder and then ranked accordingly.

All progeny should be measured and compared to their parents as well as to the flock average. In general, many sheep become coarser and the quality of the hand of the fibre decreases as they age. Comparing progeny to parents' measurements at the same age is important. For instance, fineness of offspring at one year of age should be compared to fineness of parents at one year of age, and so on.  Improved progeny should be retained in the breeding program; foundation animals should be re-evaluated and retained in the program if they still exceed the minimum standards.  As the program progresses, the standards for the selected traits can be revisited and adjusted to continue selection pressure to improve.

Breeding programs have to look at the big picture as well as the details.  Breeding animals should be selected to improve or at least maintain the general health, reproductive performance and sound constitution of the flock as well as to improve fleece traits.  Aim to correct faults and deficiencies; avoid reinforcing poor conformation.  For example, breeding together two undersized animals will result in progeny that will probably be undersized and should be avoided even if an improvement in fleece traits might be achieved.  There are always exceptions to the rules but allowing too many exceptions will weaken the flock.

As a guide, expect the offspring to fall somewhere between the better parent and the poorer parent for each selected trait. Some matings may produce offspring that show significant improvement over both parents. This is referred to as a "nick" in  breeding terms. These fortunate combinations have been known to repeat.   Animals that consistently pass on their superior characteristics to their offspring are termed pre-potent. They can be significantly more valuable than an animal with a superior phenotype that does not pass it on.   Pre-potency is highly prized in linebreeding programs geared towards fleece improvement.  Some matings are disappointing with the progeny being worse than either parent.   These progeny should not be retained in the breeding program.  It helps to record notes on the compatibility or lack of it, in the various bloodlines in your flock.  See Linebreeding.

In general, it will take a number of generations to make significant progress on a multiple trait fleece improvement program.  Don't be discouraged if the progress is slow or you encounter the occasional setback.  Learning to combine your flock's bloodlines for the best gains can be a really enjoyable part of your general interaction with your flock.  Use every excuse to get your hands into the fleeces, both on the hoof and off; it will give you a better appreciation for the progress you are making.  It often takes some time to develop the ability to feel the very small differences in fleeces, the same as it takes some time to develop an "eye" for proper conformation.   Use histograms, set up a reference binder of those fleeces that you feel are "special" and compare fleece samples to these benchmarks.  Get to know the experienced handspinners in your area.  Have them feel your fleeces and, if possible, spin up some samples and give you feedback.  Patience is a virtue in the breeding game and having your flock move toward your goals, even if little by little, is a wonderful achievement.