EPD's : what do they mean?

Unless you are an expert in these three letters, the odds are that you often ask yourself that question. Let's simply recall they are an abbreviation for Expected Progeny Difference and represent the single most accurate assessment of an animal's genetics for a particular trait. EPD's are calculated from all sources of information : pedigree, own performance and progeny.

The problem comes from the fact that different breeds have very different bases which creates confusion among commercial producers who have to keep in mind how each association calculates its own EPD's.

For example, some breeds use as their reference point the average genetic value of all calves born in a given year, say 1975. Others will choose the year 1991. If a bull in breed "A" used in 2006 is compared to other ones that were in service in 1974, he is likely to show higher numbers (EPD's) than a bull of breed "B" compared to sires used in 1990. The reason is that genetic progress has been accomplished over the years. The best way for you to make it out is to know the average EPD's for active sires in the breeds you are interested in (bulls having had progeny in the last 2 or 3 years). You will find these values in the table hereafter :

Average EPD's (active sires - 2007)
Source CE BW WW YW Milk
American Angus Association 5. 0 2.2 40 74 19
American Red Angus Association 6. 0 0.4 32 57 17
American Shorthorn Association 0. 3 1.8 15 24 3
Canadian Angus Association (Noir) - 2.9 36 63 14
Canadian Angus Association (Rouge) 5. 1 1.0 28 48 14
North American Charolais Evaluation 5. 0 1.3 21 36 6. 1
North American Gelbvieh Evaluation 102. 0 2.5 39 70 18
North American Hereford Evaluation -0. 2 3.7 41 67 16
North American Limousin Evaluation 6. 2 2.1 39 73 19
North American Simmental Evaluation 1. 7 3.3 38 63 8
Programme d'analyse des troupeaux de boucherie du Québec 0. 0 0.0 0 0 0

Now, you should be able to appreciate that an Angus bull showing a +30 lb yearling weight EPD in the AAA system (American Angus Association) is 44 lb below average for that trait (30 lb - 74 lb = -44 lb). (See table below). On the other hand, another Angus sire showing a +5 lb EPD for the same trait in the PATBQ System will be 5 lb above breed average (5 lb - 0 lb = +5 lb) because the base is set back to zero each year. This example illustrates why we cannot compare EPD's of different sources. Doing so would be like comparing Fahrenheit and Celsius temperatures !

You will note that the EPD's usually come with an accuracy value (ACC %). The more information, the greater the accuracy where values range from 0 to 99 %. A percentile (Top) rank is also given. For example, a value of 20 % for milk indicates the bull is amongst the top 20 % of its breed for that trait.
CE : Calving Ease BW : Birth Weight WW : Weaning Weight YW : Yearling Weight
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