Sheep Flock Improvement Program EPDs

Table of Contents

  1. Introduction
  2. What is an EPD?
  3. How are EPDs Expressed?
  4. What is the Difference Between the Old Indexes and EPDs?
  5. What is the Accuracy of an EPD?
  6. If the Accuracy of the EPD is Low, Would It be Better to Use the Old Contemporary Group Index?
  7. What Traits are Evaluated?
  8. What Do You Need to Know to Use the EPD Values?


Producers interested in performance now have the tools that will allow them to make genetic improvements more reliably than in the past. The new genetic evaluations are now available for lambs as they are tested on the Sheep Flock Improvement Program (SFIP). Canada is a world leader for genetic improvement in the dairy and swine industries. Now a similar evaluation system is available for sheep producers.

Enrolled producers will receive across flock evaluations for weight gain traits, milking and mothering ability to weaning and number born and reared to weaning.

What is an EPD?

An EPD (Estimated Progeny Difference) is an estimation of the genetic value that an animal will pass on to its progeny. An EPD uses all performance information on the relatives of the animal as well as the animals own performance. Animals with the best EPDs for a trait have the highest probability of producing exceptional progeny for that trait.

How are EPDs Expressed?

EPDs are expressed in the same units in which the trait is measured. For example, number born is measured in lambs, so number born EPDs are also expressed in lambs. It is important to remember that EPDs are expressed as a genetic difference from the average animal of the breed for that trait. Therefore, an animal with a number born EPD of +.10 means that the progeny of that animal on average will have .1 more lambs than the average animal. This is not the performance. If the average animal would have 1.9 lambs per lambing in your flock then this animal would have 2.0 lambs per lambing in your flock. These sound like very small numbers however, they represent the genetic differences between animals. Also, flock calculations show that these small numbers can be deceiving. For example, a flock with 200 ewes lambing will have 20 additional lambs from the +.1 animals which translates to $2,000 at $100 lambs with very little additional cost. However, it is important to note that maternal traits take a generation longer to be expressed than growth traits. For example, if you buy a ram which will improve numbers born, the ewes that he is bred to will not have more lambs. It is the daughters that you keep back in your flock that will have more lambs.

What is the Difference Between the Old Indexes and EPDs?

The old indexes only compare animals within a contemporary group. They are based solely on the animals own performance record for that lambing and do not relate to animals in other lambing groups or flocks.

The new EPDs are based on the performance of all of the relatives of the animal in addition to the animals own performance. They can be used to compare all of the animals in the flock regardless of lambing group. EPDs can also be used to compare the breeding potential of animals from different farms.

What is the Accuracy of an EPD?

Accuracy is an indication of how much information was available to evaluate the trait for an animal. Accuracy ranges from 0% to 99%. As the accuracy improves it becomes more stable. An accuracy of 90% is not expected to change very much even as new information is added to the evaluation. But an EPD with an accuracy of less than 50% can change considerably.

If the Accuracy of the EPD is Low, Would It be Better to Use the Old Contemporary Group Index?

No, the EPD is still the best genetic evaluation available even with low accuracy. It uses the same information that is used in the contemporary group index plus information on other relatives and adjusts for the genetic level of the flock. If accuracy was calculated for the contemporary group index it would always be lower than for the EPD for the same trait.

What Traits are Evaluated?

Birthweight - Direct

This is the lambs own ability to grow in the womb.

Birthweight - Maternal

This is the maternal effect on birthweight. I.e. Physical size of the womb or body cavity in which to carry the lambs.

50 Day Gain - Direct

This is the lambs own ability to grow from 0 to 50 days.

50 Day Gain - Maternal

This is the effect of the ewe on the lambs growth to 50 days. I.e. Amount of milk available and mothering ability.

100 Day Gain

This is the lambs own ability to grow from 50 to 100 days.

Number Born

This is the number of lambs born per lambing. This does not consider how often the ewe lambs.

Number Weaned

This is the number of lambs weaned by the ewe per lambing.

The number born and weaned and maternal growth traits will not be expressed until the lamb is a mother or sires lambs that become ewes.

What Do You Need to Know to Use the EPD Values?

To use EPDs effectively, you must know what you want to change about your flock and what you want to keep the same. For example, do you want the lambs to be born bigger or smaller, gain faster, have more muscle or have triplets instead of twins? It is important to spend some time thinking about your ideal animal. For example, if you purchased a ram to increase the number of lambs born and just bought the animal with the highest EPD for number born. An exaggerated case may be that every ewe lamb off of that ram had 4 lambs in their first lambing and were very small, had a high stillborn rate and the ewes did not have enough milk. In this case if you decided how much you wanted to change the trait and tried to choose the ram accordingly you would be more satisfied than just buying the highest number.

EPDs are a useful tool to change specific traits. It is difficult and usually impossible to find animals which are exceptional for all traits. Tables are available listing the range of EPD values for each trait and breed. These tables give you the information needed to determine whether the animal is in the top 25% for the trait for the breed or the top 1%. The EPDs cannot be used across breed since each breed has a different average for the trait.

EPDs are useful for the selection of animals at home or when purchasing breeding stock. If you keep SFIP records at home you will have average EPDs for your breeding flock. Then, when purchasing an animal or selecting replacement animals in your flock you can choose animals which are above your flock average for the traits that you want to change.

It is also important to know that an EPD is a reflection of the average performance of progeny. The individual performance of progeny will vary significantly, but on average you can expect the estimated performance.

For more information:
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