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Some basics about using EPDs to select breeding stock

There are a lot of ways to assess a bull and decide on its value. The age-old method of visual appraisal is where some people start and stop in terms of deciding on the value of a potential sire. Others add pedigree into their criteria, still others performance data and others use tools such as EPDs. In reality, a combination of some or all of these tools is likely the most effective tool we can use in our sire selection decisions.

It is important to remember when buying a bull that he is an automated DNA delivery system. In other words, we are not actually interested in the bull. What we are truly interested in is the DNA that he can pass on to his offspring, setting up their genetic code for success under whatever our management situation happens to be. When we assess a bull, we are really trying to figure out what his DNA might be and if he is capable of delivering it. That’s why we need to have a semen test on a bull and probably want to see how well he walks. Most people will have an idea of what they are looking for in terms of appearance from a bull and will also have an idea about what they want to see for his performance numbers.

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Most bull sale catalogues I see contain raw performance data. By that I mean, they include the birthweight, calving ease, weaning weight and yearling weight of the bull. A few may contain carcass ultrasound as well. Basically, these numbers indicate the actual performance of the bull. They also provide a limited amount of information about the bull’s DNA and are not comparable across herds or different management scenarios. For example, if we had two bulls, A and B, with weaning weights of 600 and 800 pounds respectively, which bull has the DNA for the heaviest weaning weight? If both bulls are in the same sale catalogue and were from the same herd, you would probably be fairly accurate in guessing bull B, but what if B was from a different herd than A and herd B owned a creep feeder and weaned a month later? It gets harder to tell which bull has the DNA we really want.

Another challenge with the numbers is that they may focus us on the wrong bits of DNA. For example, many producers will focus on raw birthweight in their sire selection decisions. They do this, particularly for bulls to be used on heifers. The birthweight is being used as a way to identify DNA for calving ease, which is what we are truly interested in when mating heifers. When used in this manner, birthweight actually tells us very little about a sire’s potential calving ease DNA.

Using EPD tools

Currently EPDs are the best description of a sire’s DNA in relation to other animals in the breed. There are a lot of misconceptions about EPD but they are the best available tool we have to describe the DNA that a potential sire contains. There are several reasons for this, but it boils down to the fact that an EPD effectively removes environmental differences between animals and uses pedigree information to combine performance and DNA test information to figure out what DNA an animal contains for a trait, relative to other animals in the breed. Unfortunately, we don’t have EPD for every trait that matters in beef production. It is also unfortunate that the ideal animal for a specific purpose is unlikely to have the highest EPD for any or all traits. This is in fact the most common trap that we run into as users of EPD when selecting sires.

1. Adapted from Bullock D., M. Enns, L. Gould, M. MacNeil and G.P Rupp. Utilization. 2002. Chapter 6. IN: Guidelines for Uniform Beef Improvement Programs. 8th ed. Reproduced from National Beef Cattle Evaluation Consortium Sire Selection Manual
2. Heat, cold, parasites, disease, mud, altitude, etc.3. Ability to store fat and regulate energy requirements with changing (seasonal) availability of feed.4. Physiological tolerance to heat, cold, internal, external parasites, disease, mud, and other factors.5. L=Low,M=Medium,H=High
At the most basic level EPD describe differences in performance of a sire’s offspring when mated across the same group of cows and it is expressed in the unit of measure for the trait. For example, if we looked at two bulls, A and B, and A had a weaning weight EPD of 50 and B had an EPD of 100, we would expect the average weaning weight of calves from bull B to be 50 pounds heavier than bull A when used across the same group of cows. A description of some common EPD are shown in the next table below.

For example, a producer may be buying a Charolais bull for use on cows but will put extra emphasis on calving ease. The calving ease EPD is based on calving difficulty from first-calf heifers. If we are using the bull on cows, we do not need a bull in the top 15 per cent of the breed for calving ease. We could likely use a bull with lower calving ease and more growth and improve our profitability.

Likewise, if we are looking at a bull from which we are selling feeder cattle and not keeping any heifers, we don’t need to look at the milk EPD number, since we are not keeping heifers. If we are keeping heifers, milk is a good example of a trait that we may want to keep somewhere in the middle. Many people planning to keep heifers will want a bull near the top of the breed for milk. This is fine if you have the environment to support it. Imagine a Holstein cow. It would have a very high milk EPD, but will also consume vast amounts of feed to produce that milk. If you don’t have high feed availability, it is likely that you don’t want that much milk.

A description of common EPDs.

It is important to have an understanding of what a potential sire is being used for and what your production system and environmental limitations are. A good explanation and rough guideline is contained in the following table.

There are a lot of breeds and each may publish several EPD, including many that are not on the accompanying list . When comparing EPD remember a few simple rules:

  • EPD describes if an animal will pass more/less genetic merit for the trait you are comparing
  • EPDs do not describe the specific performance on your farm, but the relative average differences between sires when mated to similar groups of cows
  • You may (probably) do not need to use every EPD for every decision. Some traits may be irrelevant to a decision, depending upon how you are using the bull (example: Sustained Cow Fertility for a Terminal Sire)
  • You most likely do not need the highest EPD for a trait and certainly not for every trait.
  • Common Sense combined with EPD are the most powerful selection tool we have

There are a lot of EPDs not presented here. There are many good tools to further explain their use. It is recommended that you visit the breed association website for specific information about their breed average EPD, available traits and other specifics.

About the author

Contributor

Sean McGrath is a rancher and consultant from Vermilion, Alta. He can be reached at [email protected] or (780) 853- 9673. For additional information visit www.ranchingsystems.com.

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