Selecting Rams - using Australian Sheep Breeding Values (ASBVs)

When selecting rams for a commercial enterprise the first step is to set your breeding objective. Spend a few minutes to write down precisely what you are aiming for, including the levels of performance and by when you want to achieve it. Find more information on setting a breeding objective.

Because the most effective way to select for a trait or characteristic is to directly measure or assess that characteristic, you should buy rams from a stud that objectively measures or collects scores (using a standardized system) for the traits you wish to improve.

For instance, staple strength can be selected with much higher accuracy if the stud directly measures staple strength on its rams, rather than just having the ASBV calculated from related measurements such as fibre diameter coefficient of variation.

However, the ram’s own performance is only part of the picture. What you see in the ram isn’t necessarily what you will get in the progeny because much of the ram’s performance is a result of the ‘environment’.

Nutritional differences between animals are a key environmental element and not only come from what they eat, but whether they were born or reared as a twin or their mother was a maiden ewe—giving them less nutrition during pregnancy and lactation than for a single lamb and/or from a mature ewe.

Also, climate, disease and management differences will affect how they perform.

If you know these environmental factors for each individual, and if you have been able to inspect all of the animal’s relatives and see their performance data, you’d be able to predict very accurately, how the progeny will look and perform.

However, this is not practical for you to do, so studs that provide you with Australian Sheep Breeding Values (ASBVs) already have this information taken into account. Pedigree information, management groups, data from relatives and relationships to rams used in the stud and elsewhere are all accounted for and very important when calculating Australian Sheep Breeding Values.

Importantly, you can accurately compare rams from different studs (whether at opposite sides of the country or having had quite different management) if they both provide ASBVs for the same trait.

How do you incorporate ASBVs with your visual selection?

Choosing your stud(s).
The last decade has seen great changes in the information some studs offer and ram buyers have become more discerning. Gone are the days of believing that a ram simply throws back to the average of the stud, as more detailed analysis has shown that there is considerable variation across rams within a stud.

Comparing rams from different studs is easy and accurate when they have ASBVs because the differences associated with nutrition and management have been removed.

1. Choose one or more studs that have the type of sheep you are after and which provide ASBVs directly measured on the traits you consider are important to your production system.
2. If the stud you are using does not currently provide ASBVs, ask them to do so. An increasing number of studs are now providing ASBVs because their clients have requested them.
3. Ask for the ASBV data to be sent to you in advance—more studs are now providing this in sale catalogues and on the web (including links to their animals in LAMBPLAN and MERINOSELECT ). This is particularly useful to compare studs at the start of the sale season, allowing you to review the rams on offer from each to see whether one stud has more rams that suit you or whether there are individual rams you would like to inspect.
4. Based on your review of sale information, choose the stud sales you will attend.

Choosing individual rams

Visual selection is still an important part of selection—particularly for wool sheep—because there are still traits of importance that are not available for selection using ASBVs.

1. Choose the minimum level or range of ASBVs (or an index) that you will accept for each trait that is important to you.

• For instance, you may choose a fibre diameter ASBV range between –1.0 and –2.0 microns, so as to keep your flock’s fibre diameter in the fine-medium range. On top of that you might want worm resistance and are willing to take animals that are simply “better than the average for all Merinos”. This is about –10% for WEC ASBVs.
• Be realistic in the levels you set and the price you may need to pay, as many others will also want the higher performing rams.
• Rams with lesser performance can be just as profitable for you providing you pay a correspondingly lower price, as the ram’s costs should also be included in your cost of production; likewise the best animals may not be the best value if they are too high a price. Use the Sheep CRC’s Ram Value Calculator to compare values based on ASBVs.
• It is also suggested that you start with only the 1 or 2 most important traits and an index when you are learning to use ASBVs; add more as you become confident.

2. Shortlist the rams based on your criteria, so that you can then spend your time at the sale more thoroughly visually assessing these, instead of wasting time on poorer performing animals.

3. On sale day, follow your shortlist and visually assess only the selected individuals. Avoid viewing poorer performing animals, so you are not influenced by those that look good, despite their poor performance.
 

Selecting rams with no ASBV data
Studs that do not provide ASBVs can certainly have good individuals, however, accurately identifying them is more difficul:

• which are the best individuals within the stud, and
• how do they really compare to rams from other studs?

Within stud selection
If some raw measurements or scores are provided, these can be useful if the following applies.

Firstly, the animals that have been measured/scored should have all received equal nutrition and management, in other words, they needed to have been run together until when their measurements were taken. If not, this data can only be used to compare any animals that were managed together.

Secondly, the traits measured need to be able to be passed onto their progeny. Traits with higher heritability, a larger range in their expression and which can be measured very accurately are those where selection will be most successful. Good progress can still be made if, for example, only one of these factors is high or two of them are moderate.

Using a raw fibre diameter result is suitable as it has a high heritability, it can be measured quite accurately and there can be a wide spread of measurements within a related drop of lambs. Conversely, using raw worm egg counts for individuals is not so suitable as the WEC measurement itself is reasonably inaccurate, although it is moderately heritable, and has a wide expression within a mob. For traits such as WEC, the data of relatives must be built in to provide an accurate figure for selection; this can only be done with ASBVs.

Thirdly, take account of the birth and rearing status of the individual (e.g. born a twin, raised a single) as well as the age of his dam (maiden versus mature ewe). If the stud does not provide this information then you will almost certainly favour the single born lambs reared by mature ewes. This will be at the expense of genetically bigger, finer and heavier fleece weight rams that happen to look smaller and broader and lighter in the fleece, because they were twins and/or were born to maiden ewes. The exception is that when selecting for less wrinkle, you’ll favour sheep that are twins, were born from maiden ewes or were born in a drought, because the lower nutrition results in fewer wrinkles.

Across stud selection
Without Australian Sheep Breeding Values, determining how individuals in one stud objectively compare to extremely difficult as management and nutrition differences account for such a large part of performance.

Choosing rams that have been shown is one way, but heavily reflects the ability of the studmaster to feed and prepare their animals. You can also use results from bloodline comparisons (wether trials).

Rams run and measured under conditions most similar to your own (i.e. unhoused, uncoated, pasture-fed) will provide the most selection accuracy.

In conclusion, Australian Sheep Breeding Values are now available on rams from many studs. ASBVs offer:

• The ability to far more accurately predict the performance of progeny than using raw data or no data
• The ability to compare animals from different studs or different age or management groups within one stud
• A means to shortlist potential purchases for later detailed visual inspection.

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