Selecting the Right Ram with EPDs

Table of Contents

1. EPDs - Estimated Progeny Differences
2. Advantages of EPDs Over Indexes
3. How to Use EPDs - Buying a Ram
4. Conclusions

EPDs - Estimated Progeny Differences

An EPD is an estimate of the genetic value that will be passed onto the progeny of that animal.

Usually, the reason why producers are concerned about genetics is because they particularly like the performance of an animal and want to be able to repeat that performance in the flock. Performance is a product of genetics and environment. For example, if I measure gain from 50 to 100 days on a number of different lambs, even though the lambs were fed and treated the same they will not all gain the same amount - this is a genetic effect. If I take twins and feed one only hay and the other only creep, they will not gain the same amount - this is an environmental effect.

So, in order to change performance there are two choices: change environment or change genetics. Changing environment or management can have a huge impact on many traits; however management changes are only evident as long as you continue the new practice. Therefore, when you are buying an animal you want to know whether good performance is due to good management or good genetics.

Heritability gives us an idea of how well a trait is passed on to progeny or how big of an effect genetics has on a trait.

For example, reproductive traits are lowly heritable. If you keep a replacement ewe lamb that is a twin, will she always have twins? Will she almost always have twins? If you don’t know anything else about the animal, it is possible she may never have twins. This is what lowly heritable means.

Carcass traits are highly heritable. If you use a ram that has a far superior carcass, for example a Southdown ram on Finn ewes. Most people would agree, almost every lamb will have an improved carcass over the straightbred Finn lambs no matter what the animals were fed or how they were managed. This is what highly heritable means.

Lowly heritable traits are highly affected by environment or management and highly heritable traits are not affected by environment or management as strongly. But any genetic change is permanent regardless of how heritable the trait.

Genetics are: variable, a single mating will not produce the same lamb every time; heritable, characteristics will be passed on to progeny; unknown, there is no method to know for sure exactly how an animal will perform before the performance takes place. But it is possible to estimate what the performance might be.

How to estimate genetics? Basically, use all the information available. Back to that lowly heritable trait, number born. In the example above only knowing the replacement ewe lamb was a twin with no other information it was anybody’s guess if that animal would give birth to twins every time or ever. But if you knew that the animal was a twin, all of the lambs born in the same group were all twins and 99% of the lambs born on the farm were twins and the animals’ dam and granddam always had twins, you would probably feel quite comfortable saying that on that farm the lamb would probably always have twins. This is exactly what EPDs do. They simply gather all of the information and estimate what the performance will probably be.

The EPDs are across flocks. The above logic is expanded then to all the animals of the same breed in the province. This across flock comparison is particularly important when you are buying an animal. One of the huge disadvantages of an index was that it was only relevant within flock. So, regardless of the index of the animal being bought you had no idea how the animal might perform in your flock until progeny were born. Unless, you had purchased from the same flock before.

One important thing to realise is that genetics are variable. For example: if you purchase a ram with a gain EPD of +1.5 kg and the ewe that he is mated to has a gain EPD of -.5 kg. Then the average performance of the progeny will be +1 kg more than if you used a ram that had a gain EPD of 0. Therefore, because of the variability of genetics some progeny will be quite a bit better than +1.0 and some will be quite a bit worse.

EPDs are available through the Sheep Flock Improvement Program (SFIP) for the following traits:

Birth Weight - Direct
Birth Weight - Maternal
50 Day Gain - Direct
50 Day Gain - Maternal
100 Day Gain
Number Born per Lambing
Number Weaned per Lambing

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Advantages of EPDs Over Indexes

1. Includes all information available in the evaluation
2. Expressed in units of the trait
3. Can be used across flock
4. Are more accurate than indexes because of relative information and therefore make it possible to evaluate lowly heritable traits  

How to Use EPDs - Buying a Ram

Rams are half of the genetics of a flock. An individual ram will be mated to many ewes, making the selection of a ram particularly important. A new ram will significantly influence your lamb crop and therefore your revenue. As a result, you don’t want any unpleasant surprises. Before you go looking for a ram, identify exactly what you want. Do you want the gain of your lambs to be better, the same or slower than last year? Do you want the lambs to be taller, shorter, thicker or thinner? Then when you go to a flock to purchase an animal you need to find out as much information as you can to try and ensure that the lambs sired by this ram will perform as expected.

Ideally, the purebred breeders would do the extensive paperwork and genetic improvement; multipliers would reproduce excellent female lines in large numbers and the commercial producer would only keep records to monitor performance in order to make management changes or decisions and to buy the genetics needed. But unfortunately, real life isn’t ideal and you may need to purchase a ram for a number of reasons.

If you are buying a ram to keep your own replacements:

• Concentrate on maternal traits
• Realise the traits won’t be expressed until the ewe lambs have lambs
• The most important traits will depend on what your production system entails
• Maternal traits are lowly heritable, genetic changes will be small and slow
• Maternal traits can have a big impact economically so small changes are worth it economically. 

Some of the important traits are:

• Number born
• Number weaned
• Body capacity
• Milking ability
• Mothering ability
• Lambing interval 

When you decide what traits are most important make sure you know average numbers for the breed. Ask the breeder what the average numbers are: for his/her flock, for the group the potential ram was raised in and for the potential ram itself. This gives you an idea of how the animal might perform in your flock. If there are EPDs for the trait, the following example gives an idea of the information that can be determined. 

Example

Assume you would like to increase the number weaned per ewe in your flock. If you keep 40 ewe lambs sired by the new ram, if your new ram has an EPD of +.3 lambs weaned, if your ewe flock has an average EPD of 0 for number weaned, then you would expect 6 additional lambs weaned as per the following calculations.

An estimate of the average EPD for the ewe lambs kept

= (+.3 + 0) ÷ 2
= +.15 lambs weaned 

The number of additional lambs weaned would

= 40 x .15
= 6 additional lambs weaned 

If lambs are worth $100, there is a potential $600 of additional revenue every time those replacements lamb. 

If you are buying a ram to use as a terminal sire:

• Concentrate on ideal market lamb traits
• The most important traits will depend on the type of lamb that you want to market
• Traits tend to be medium to highly heritable
• These traits will be expressed in the direct progeny 

Some of the important traits are:

Carcass characteristics

• loin eye area
• muscling
• dressing %
• finish 

Growth characteristics

• gain to weaning
• post-weaning gain

Wool characteristics

• tight fleece

If you market mainly newcrop lambs, you may want a well muscled lamb that gains reasonably quickly and has a tight fleece at 60 - 80 days of age. Carcass characteristics are highly heritable and difficult to measure on a live animal. This means that you can simply look at an animal and have a good idea as to whether the general muscling of the ram is similar to or better than what you have used in the past and how good the lambs may be. Growth characteristics are mediumly heritable so it is more difficult to simply look at a yearling ram and tell how well the animal gained. i.e. was the best animal in the pen this year better, worse or the same as the best animal in the pen last year.

Example

Assume you want to increase your weaning weight. If you will be marketing 60 lambs, if your new ram has an EPD of +3.0 kg for 50 day gain - direct and if your ewe flock has an average EPD of 0 kg, then you can expect $316.80 of extra revenue as per the following calculations.

An estimate of the increase in weight passed onto the progeny
= (+3.0 + 0) ÷ 2
= +1.5 kg 

The extra weight at weaning
= 60 kg x 1.5
= 90 kg

Extra revenue if sold as newcrop
= (90 kg x 2.2 lbs) x $1.60/lb
= 198 lbs x $1.60/lb
= $316.80 extra revenue 

This assumes that you are marketing newcrops right off the ewes and you want to wean at a set time. Therefore the lambs gaining faster gives you more weight to market and you don’t have the choice of simply waiting until the lambs are a little heavier. If you have the option of waiting there is still extra revenue in the form of better feed conversion.

Conclusions

In order to make sure that you make the best possible purchase, you should:

1. Make sure you know exactly what you want the ram to do in your flock
2. Make sure you know average performance for the traits in the breed
3. Find out as much information about the traits in the flock from which you are purchasing as possible.
4. Understand what the performance numbers mean so you can: 
   • decide if the flock is selecting for the traits you want
   • decide if the ram will do what you want in your flock
   • decide if the ram did improve your flock 

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