Buying merino rams
This information note aims to assist ram buyers interpret raw measurements on animals to better select rams for individual needs.
Interpreting measurements on rams for sale can be difficult because of the effects of the environment. What we see and measure is affected by both the animal's genes and by the environment in which the animal has been run. For many of the traits important to wool production, the majority of the performance variation we measure is due to environment and the rest is due to genetics. The aim in selecting a good sire is to choose the ones with the right genetics for the job, not the ones that have had the best feed.
Estimated Breeding Values, or EBVs are selection tools that are available for use in both sheep and cattle industries. In the sheep industry these are called Australian Sheep Breeding Values (ASBVs). These values provide an indication of the potential breeding values of different animals. Understanding and selecting animals with ASBVs can be sourced through the Sheep Genetics and MerinoSelect websites.
In the absence of the availability of ASBVs, some simple questions and an understanding of how to interpret measurements can help with the selection of the best rams for the job.
The genetics may be good, but if the ram is not sound, he will not be able to work so the structural conformation needs to be acceptable before considering other traits and measurements. A simple checklist includes the five 'Ts' - the Teeth, Toes, Tossle, Torso and Testicles.
Is everything as it should be?
- Can he eat properly?
- Can he walk properly?
- Is his tossle working?
- Is he in good condition/ health?
- And are his testicles firm- with no lumps or bumps?
The core measurements that effect financial and management returns for wool production are:
- Average fibre diameter
- The spread or variation of fibre diameter
- Fleece weight
Although these traits are highly heritable (i.e. they can be improved by breeding), they are also very much affected by nutrition, age and where and when samples were taken for testing. If using the actual measurements to select rams, these things need to be taken into account.
Other traits like wool quality, skin traits and body size will be included in most selections, but some of these will differ depending on individual needs.
The Fibre Diameter, (FD), measured in microns, (m), of a ram available for sale may not be a good indicator of what he will breed, or even indicate the average micron of his fleece at the next shearing. The age of the sheep and its' management and nutrition can significantly affect the fibre diameter.
Age and sex effect
The age at which the fibre diameter of the wool of a ram is measured can have a significant impact on the micron test. If nutrition and environment are kept constant, the micron of the wool generally increases until the age of about of 2-2.5 years, when it will gradually plateau, (see Figure 1). Not all animals do this, but this is generally the trend.
Figure 1: Age and sex effect on Fibre Diameter
The quantity and quality of the pasture or supplementary feed available to a ram can also affect the micron of the wool. The micron of the wool will usually be high in spring when the quantity and nutritional value of the pasture is maximised, (Refer to Figure 2). Similarly it will be higher in any period of feeding in preparation for sale
Figure 2: Effect of Pasture Growth on Fibre Diameter
The time at which a ram is shorn and sampled for testing will therefore affect the fibre diameter result.
Figure 3: Effect of time of shearing and sampling on Fibre Diameter measurements
Hence the actual measurement of an animal can vary significantly, depending on when it is sampled.
In this example he may test 20 or 23 micron, but he will still breed the same. Fibre Diameter information can be provided as deviation from the average of the flock, which is zero. This is better than relying on the measure of the animal alone, providing all animals have been run and managed together and can be compared. It provides a good guide as to how an animal's progeny will perform compared to others in the mob. A ram that measures 19 micron at sale may reveal little about his potential performance when taken home.
If you are looking at rams from a stud you haven't used, then a guide to the average wool clip fibre diameter of the stud over a period of time is a useful guide as to how the sale rams might breed, especially if run in a similar environment to your own. Clip information over a three year time period will be a better indication of the genetic trend as it will show results over different seasons.
Fibre diameter variation
Fibre diameter will vary both along each fibre, and between fibres.
Figure 4: The variation in fibre size between fibres and variation of m along the fibre.
Both variations are measured as Standard Deviation (SD) of Fibre Diameter and the Coefficient of Variation (CV) of Fibre Diameter.
Standard Deviation (SD)
This is the measure of the spread of the variation around the average fibre diameter. For example, a SD value of 4µ means that two thirds of the sample may be +/- 4µ from the average.
As a guide, average measures of standard deviation in samples of different wool types would be:
|Fine Wool||19m||SD 3.25m|
|Medium Wool||21m||SD 3.6 m|
|Strong Wool||24m||SD 4.1 m|
Coefficient of Variation (CV)
This is the standard deviation expressed as a percentage of the average fibre diameter. It relates the amount of variation in fibre diameter to the average fibre diameter which is useful because SD increases as FD increases. The lower the CV value means less variation within the sample.
Selecting animals with less fibre diameter variation is unlikely to attract a price premium, however selecting animals with low CV can help select for better staple strength, reduced susceptibility to fleece rot and can be of some benefit to processors through finer spinning performance.
As nutrition affects Fibre Diameter, along the staple, then it follows that animals that have had large nutritional variation over the wool testing period can have larger variation along the staple. Therefore SD and CV are both also affected by nutrition.
It has been found that wool that has more than 5% of fibres with a fibre diameter greater than 30m is likely to cause prickle or itchiness when worn next to the skin. The Comfort Factor is a measure of the percentage of fibres that are less than 30m and so a Comfort Factor of 95% or greater, implies 'comfort.'
Comfort factor measurements need to be treated with caution as they measure only a small proportion of the fibres in total. The lower the Mean Fibre Diameter (MFD) the less likely there will be very coarse fibres.
Coarse Edge Micron (CEM) is the number of microns greater than the mean, where the broadest 5% of fibres begin.
Fleece weight is usually recorded as the weight of the fleece in kilograms, minus the belly. For a measure of fleece weight to provide information on the genetic potential to grow wool, measures of wool cut should be taken from animals that are at least ten months old with at least six months wool. This removes some of the effect of early nutritional differences provided by the ewe to her lambs.
The weight of a fleece can be impacted by how old the sheep was when it was shorn, months of wool growth, feed and climatic conditions, whether it was shorn as a lamb and how it was reared (i.e. was it a twin or a single).
The fleece weight is given as either clean or greasy fleece weight, in kilograms.
The Greasy Fleece Weight (GFW) contains dirt, vegetable matter, suint and moisture. The grease component of the wool protects the wool and sheep from the weather, so selecting too heavily in some environments for Clean Fleece Weight (CFW) may not be wise. The grease component of the fleece is also affected by nutrition so animals that have been well fed will have more grease in the wool and so produce softer and more nourished feeling wool.
The fleece weight may be expressed as a percentage of the average fleece weight for the group of rams that are to be compared. For example, a ram with a Clean Fleece Weight of 130% means that he cut 30% more wool than the average of the mob. This helps address the affect of the environment. If a ram cut 10kg it does not mean the progeny will cut 10kg but if he cuts 20% more than the average then this means his progeny are more likely to cut higher than average too.
If all animals have been treated the same, then it is how one ram compares to the others that will show his relative performance.
Other information that may be available from studs in order to help with sire selection includes information on bloodline analyses and sire evaluations.
Ram buying check list
- 5 T's (Teeth, Toes, Tossle, Torso and Testicles)
- Wool quality
- Three year flock average micron of the stud
- Know the age of the ram at testing
- Know when the wool was sampled
- Know how many months wool growth
- Wool tested when ram was older than 10 months old and with more that 6 months wool
- Rams being compared were all run and managed together
- Wool tests from an accredited laboratory
- Other relevant information on bloodline and sire evaluation
Checking animals thoroughly before buying and asking some relevant questions will reduce the chances of taking home any surprises.
Contact/Services available from DEPI
Information notes are available from your local DEPI information centre.
This Agnote was developed by Sam Clayfield 7 September 2010.