Mike
Well-known member
The Basics of EPD's
It's hard to believe in this day and time there still exist a good deal of mistrust and misunderstanding when it comes to Expected Progeny Differences (EPDs). As a purebred breeder, it is critical that you not only understand the application of EPDs, but also how they are calculated. I don't mean the specific statistical methodology, but rather how the data you submit affects the EPDs of your cattle. If you read no further, remember this, EPDs work, but only with complete data submission and proper contemporary grouping.
EPDs are a prediction of the genetic transmitting ability of an animal. They tell you in a given environment how one animal will compare to another; they do not estimate actual weights, only weight differences. An animal's genetic value does not change over time, but the amount of information we have to estimate that value does. The difference in that animal's true genetic value and the predicted value is known as accuracy. EPDs with a higher accuracy have less chance of changing far from their predicted value. It is also important to realize that the EPD value is reflective of the average of an animal's calves and could represent a wide range.
The calculation of EPDs incorporates the relationship between all animals in the analysis, records submitted on all related animals, and the value of correlated traits (the manner in which traits affect one another). An animal's own records also play a role in their EPD. This individual performance is all based on their ratio within their contemporary group.
Contemporary grouping is how environmental differences are removed from the genetic equation. A given sire's calves will not weight the same at birth in Texas versus North Dakota and it would not be fair to compare the weight of a calf on feed with one that isn't. A contemporary group is a group of animals raised together under the same conditions. When you report weight information it is critical to properly define contemporary groups. Only calves managed similarly should be assigned the same contemporary group code. The system will further break contemporary groups by sex and age.
Maintaining large contemporary groups is vital to the effectiveness of the genetic evaluation system. Ratios are calculated within contemporary groups and this is how the genetic differences are determined. Single-animal, or single-sire contemporary groups are of little value in determining genetic differences. The best way to ensure an accurate genetic evaluation is to keep contemporary groups large and properly identify them using management codes and try to use a mixture of both high-accuracy reference sires and young sires in each contemporary group. EPDs are by far the best prediction of performance we have, but they require complete data submission and proper contemporary grouping to maximize their effectiveness.
It's hard to believe in this day and time there still exist a good deal of mistrust and misunderstanding when it comes to Expected Progeny Differences (EPDs). As a purebred breeder, it is critical that you not only understand the application of EPDs, but also how they are calculated. I don't mean the specific statistical methodology, but rather how the data you submit affects the EPDs of your cattle. If you read no further, remember this, EPDs work, but only with complete data submission and proper contemporary grouping.
EPDs are a prediction of the genetic transmitting ability of an animal. They tell you in a given environment how one animal will compare to another; they do not estimate actual weights, only weight differences. An animal's genetic value does not change over time, but the amount of information we have to estimate that value does. The difference in that animal's true genetic value and the predicted value is known as accuracy. EPDs with a higher accuracy have less chance of changing far from their predicted value. It is also important to realize that the EPD value is reflective of the average of an animal's calves and could represent a wide range.
The calculation of EPDs incorporates the relationship between all animals in the analysis, records submitted on all related animals, and the value of correlated traits (the manner in which traits affect one another). An animal's own records also play a role in their EPD. This individual performance is all based on their ratio within their contemporary group.
Contemporary grouping is how environmental differences are removed from the genetic equation. A given sire's calves will not weight the same at birth in Texas versus North Dakota and it would not be fair to compare the weight of a calf on feed with one that isn't. A contemporary group is a group of animals raised together under the same conditions. When you report weight information it is critical to properly define contemporary groups. Only calves managed similarly should be assigned the same contemporary group code. The system will further break contemporary groups by sex and age.
Maintaining large contemporary groups is vital to the effectiveness of the genetic evaluation system. Ratios are calculated within contemporary groups and this is how the genetic differences are determined. Single-animal, or single-sire contemporary groups are of little value in determining genetic differences. The best way to ensure an accurate genetic evaluation is to keep contemporary groups large and properly identify them using management codes and try to use a mixture of both high-accuracy reference sires and young sires in each contemporary group. EPDs are by far the best prediction of performance we have, but they require complete data submission and proper contemporary grouping to maximize their effectiveness.