EPDs and ABCs: A Quick Tour

Dr. Andy Robinson, Beef Improvement Ontario

May 1997

INTRODUCTION

What is an EPD? What is an ABC? If you’ve asked yourself these questions, please read on.

EPD stands for Expected Progeny Difference and ABC stands for Across Breed Comparison but what do they really mean, how are they calculated and how can they be used? By the end of this brief article, I hope you know the answers to these questions.

SELECTION and IMPROVEMENT

Since before recorded history, mankind has been working on improving domestic livestock. The variety of different pure breeds of beef cattle demonstrates that selecting and breeding cattle with specific characteristics decade after decade leads to genetic improvement. Each of the different pure breeds available today is the result of long years of selection for the visual characteristics that make each breed unique. However successful it was, that process is now too slow for the fast pace of today’s cattle business. What we need now are accurate, state-of-the-art tools to advance beef cattle performance at a pace that matches the needs of today’s industry. To get this rate of progress, we need to use EPDs and ABCs to select the best animals and create the next crop of superior calves.

EPDs and ABCs are selection and improvement tools, just as visual appraisal, actual or adjusted weights and other measurements are. What I hope to show you is that EPDs and ABCs provide a more accurate picture of the genetics of an animal than the visual appraisal and actual or adjusted weights do. By using EPDs and ABCs in balance with visual appraisal and actual or adjusted weights, you will make better progress in improving your genetics and the profitability of your herd.

EXPECTED PROGENY DIFFERENCES

What’s in a number? An EPD tells you how the calves from an animal will compare genetically to an average group of animals in the same breed. For example, an EPD of +40 for yearling gain says that the progeny from this animal will have the genetic ability to grow 40 lbs more than average after weaning. EPDs are always relative to some reference group so an EPD is always more (+) or less (-) than the average. The trick comes in knowing what the average is. Currently, BIO uses a rolling base so "average" means the average of all calves born in the last 3 years. Each year the base average "rolls" ahead one year which makes the reference point "roll" along with the improvement in the cattle. Many breed associations use a fixed base so "average" is a group of calves born some years back in the past. This group of calves doesn’t change from year to year so the base is "fixed". EPDs on a rolling base enhance genetic improvement because they are compared to a moving target which is always raising the performance bar. EPDs on a fixed base provide a constant measure of improvement but it is easy to get lulled into a false sense of security if you don’t know what the current breed average is. For example, if an animal has a fixed base EPD of +40 but the current breed average is +38, on a rolling base that EPD would only be +2 even though it seems like more. The moral of the story: be sure of the base and average level when using EPDs.

 

ACROSS BREED COMPARISONS

An ABC is a BIO specialty. An ABC is an EPD that has been adjusted for differences between breeds and accounts for heterosis (crossbred vigour). A BIO ABC has a rolling base just like an EPD but instead of comparing just within the breed, an ABC can be used to select across many breeds. ABCs are specifically designed for commercial cow-calf producers who are making selection and bull buying decisions for a cross-breeding program. By using ABCs, the best animals in a diverse group of breeds and crosses can be easily identified. The rolling base average for the ABCs are all the calves in the BIO database for the last 3 years.

 

CALCULATING EPDs and ABCs

EPDs and ABCs are calculated together and the process for calculating EPDs and ABCs is the same up to the last step (breed differences) so I will describe it as one process. Many people have asked me for the formula for an EPD. I’m afraid it just isn’t quite that simple. Although the basis for an EPD is a simple formula, the process is complicated and pulls in a lot of information from parents, other relatives, herd mates, traits, etc. The more information that is included, the more complicated the calculation gets. Each animal evaluated has its own formula that changes depending on how many calves, weights, relatives, etc. that each has.

Back to the beginning. An EPD is based on a simple formula. An animal’s performance for a particular trait (let’s call it P) is made up of the animal’s genetics (let’s call it G) and how those genetics interact with the environment (let’s call it E). So we can write this interaction as an equation:

P = G + E

What this equation says is that the performance that we can measure is a result of the animal’s genetics interacting with the feeding program, weather, pasture conditions and many other factors that make up the environment.

When we calculate an EPD we want to accurately identify things that affect E so our calculation of G is the best possible.

So how do we separate G and E? We don’t need to know everything about how every animal was fed to measure E. Instead, we define groups of animals that were in the same environment and see how they each responded to that environment. By looking at differences in their response, we can separate their genetics. How do we define the environment? We group animals by herd, year, age and management group. This grouping accounts for differences between:

• herd owners and their cattle management practices,
• years and the effect of wet or dry summers on pasture conditions etc.,
• age groups (mature cows produce more milk than first-calf heifers),
• management groups which provide extra detail about how cattle have been fed or handled.

All of these components together make up the environmental differences between animals. How do we look at G? We know that ½ of the genes in every animal come from the sire and ½ of the genes from the dam and so on back through the pedigree. If an animal has calves, ½ the genes in each calf came from that animal so each calf is included also. We include all the relatives of an animal in calculating G and we get as much information as possible.

When it’s all said and done, the general formulas for an EPD with all this extra detail are shown below.

G becomes:

Animal’s EPD =

factor1 * (records - environment) +
factor2 * average of parents +
factor3 * (progeny - 1/2 mate)

E becomes:

Environment =

factor4 * records +
+factor5 * breed/age/sex adjustment
+ factor6 * EPDs of animals in that environment

We add a piece for differences between breeds, the age of the dam and the sex of the calf:

Breed/Age/Sex =

factor7 * records

+ factor8 * environment

+ factor9 * EPDs of animals of the same breed/age/sex

Each of the "factors" is customized for each animal to account for each animal’s own unique circumstance. You’ll also notice that all of the equations have pieces from each other. This is how the equations start to get complicated.

Rather than understand these equations in all their gory detail, the essential message to take from this is the amount of information that is considered in calculating an EPD.

USING EPDs and ABCs

EPDs and ABCs are designed as a selection tool. In order to effectively use EPDs and ABCs to improve the genetics of your cattle, here are some general steps to follow:

1. identify the goal(s) of your breeding program
2. decide which EPDs or ABCs match your goal(s)
3. select the best animals in your herd that rank the best for the EPDs or ABCs you identified in step 2. above
4. look at any secondary traits to decide amongst the best animals (for example, temperament, structure, etc.)
5. make the breedings that your selection process has identified

To use EPDs and ABCs to purchase replacement bulls or heifers, the process is similar:

1. identify the goal(s) of your breeding program
2. decide which EPDs or ABCs match your goal(s)
3. select the best replacement animals for your herd by the EPDs or ABCs you identified in step 2. above
4. look at any secondary traits to decide amongst the best animals
5. purchase the animal(s) and make the breedings that your selection process has identified

PRACTICAL EXAMPLES

To help round out this quick tour, let’s look at some examples of using EPDs and ABCs in a selection and breeding program.

Suppose we have a herd of 30 commercial cows. We want to identify the best cows in the herd to produce replacement heifers and we want to buy a bull from the local bull evaluation centre. This is a commercial herd so we’ll use ABCs in the example but it works equally well with EPDs to select within breed.

Step 1 - Identify the goal

Suppose our example herd is a bit light on weaning weight. Being in the business of selling weaned calves, our market is for pounds of calf. However, live calves are important to the program so we need to include traits like calving ease and birth weight. So let’s set our goal as the production of pounds of calf weaned with low calving difficulties.

 

Step 2 - Decide which ABCs match the goal

Using ABCs for weaning gain and maternal milk will help us increase pounds of calf weaned. Using ABCs for birth weight and calving ease will help us decrease calving problems and maximize the chance of having a live calf. So, we want to look in our herd for cows that have positive ABCs for weaning gain and maternal milk. At the same time we want to look for cows that have a negative ABC for birth weight (we want to decrease birth weight) and a positive ABC for % unassisted (increased chance of calving without help).

 

Step 3 - Select the cows in our herd that match the ABCs listed above

Now, using a herd genetic report like the BIO Herd Improvement Program EPD/ABC Report - Cow Genetics, go through the list and identify all the cows that have positive ABCs for weaning gain, maternal milk and % unassisted (calving ease) and negative ABCs for birth weight. On the first pass through the list, try to be tough on these limits and see how many cows you pick. If there are more than enough for producing replacements (pick 2 cows for every replacement heifer you want) great, there’s the list of top cows. If there aren’t enough cows, lighten up the criteria a bit and make another look through the list. Once you have enough cows plus a few extra, there’s your top cow list.

 

Step 4 - Look at any secondary characteristics

Look though your top cow list again and check to make sure the cows you’ve picked also have reasonable calving intervals, good structure and temperament and any other factors you consider important for cows in your herd. If you are very strict on these factors, you will lower your progress towards your goal of producing live pounds of calf. The idea is to strike a balance here to eliminate the cows that you really don’t want to keep replacement heifers from while still sticking to the top cow list.

 

Step 5 - Make the breedings

Oops, we haven’t bought the bull yet.

Now, we’ll go buy the bull. Steps 1 and 2 are the same.

Step 3 -Select the best bull for the herd based on the traits in step 2

Using a BIO Bull Evaluation Program report from your favourite bull evaluation centre, identify the breeds you want to consider and then, using the ABCs, create a top bull list in the same way we did the top cow list: identify the bulls with strong positive weaning gain, maternal milk and % unassisted ABCs and with strong negative birth weight ABC. Use the same 2 pass system - be tough on the first try and go back and lighten the criteria if you only find 1 or 2 bulls. Finish off with a list of 3 to 5 bulls that meet the ABC criteria.

 

Step 4 - Look at any secondary characteristics

From the list of 3 to 5 bulls, look at any secondary characteristics that you feel are important. You may want to look at carcass traits like rib eye area, backfat and marbling ABCs to build in a little extra marketability for your calves. Shorten the list to one or two bulls and get out your chequebook.

 

Step 5 - Now it’s time to breed the cows

Take the bull home and get ready for breeding season.

 

WRAP-UP

That is a quick tour of EPDs and ABCs; what they are, how they are calculated and how to use them.

CURRENT GENETIC EVALUATIONS

Through better technology, BIO generates up-to-date evaluations for over 3 million records every week. For a minimal fee, you may request current Bull Evaluation Performance Certificate or Cow Production & Performance Record.