By Lance Bauer, Director of Breed Improvement & Western Field Representative
Starting with this article I will discuss the other factors that go into the calculation of EPDs, other than the measured traits that have been mentioned previously. These factors are what allow us to take out environment and estimate relatedness, in order to calculate EPDs. The first factor that I will discuss is contemporary groups, and basically a contemporary group are animals of approximately the same age and sex that have been managed the same. By properly forming contemporary groups the environmental effects can be taken out in the calculation of EPDs. In the calculation of EPDs the difference of the measured trait against contemporaries is what is important. For example, if there is a 50 pound difference between weaning weights of two animals it does not matter if the weights are 550 pounds and 600 pounds, or 750 pounds and 800 pounds the EPD calculation will not change. This is why it is important to properly form groups, so that accurate comparisons can be made.
Contemporary groups for birth weight are based on the owner of the cow at the time of birth, the sex of the calf, the birth year, the birth type, and the age of the dam. It is a good idea to try to keep calves born to cows/heifers that are managed the same in the same contemporary group, provided they are all born within a reasonable calving season. The easiest way to deal with birth contemporary groups is to have a defined calving season and use that as a contemporary group. Embryo Transfer (ET) calves are treated differently and will be in a contemporary group of one, unless the breed of the recipient dam is noted. If there are several calves out of the same recipient dam breed, then they can be in a contemporary group together. Calves that are the first progeny of a dam are grouped differently than calves out of cows that have had a calf previously. A breeder can also define contemporary groups by providing a birth group.
Weaning weight contemporaries are based on the original herd, the sex of the calf, the year of birth, the management group and management code, and ET vs natural calves. Calves that are raised the same and are of the same sex at weaning are an easy way to make a weaning contemporary group. When creating a weaning contemporary a breeder can assign contemporary groups using a management code and custom weaning group. Management codes define how the calf was raised until weaning, whether the calf had access to creep feed, if the calf is an ET calf or if the calf was raised by a foster dam. Again, calves out of recipient dams will be grouped alone, unless a breed of dam is provided for the recipient. The weaning group is defined by the breeder and each group should have a different letter or number designation. Making sure that there are several calves in a contemporary group is important for information to be valuable for the genetic evaluation.
Yearling contemporaries are based on the original owner, the sex of the calf, year of birth, the management group and management code, the type of calf, and previous contemporary group. Calves that are weaned at the same time and managed the same until yearling weights are taken can be kept in the same contemporary groups. If some of the calves weaned together are taken to another pasture and raised differently then they will become their own contemporary group. Animals that are in a weaning contemporary group can stay in a group through yearling as long as they are raised the same way until that point. New animals cannot join a yearling contemporary group. The management codes for yearling weights deal with how much if any the calves in the group were fed from weaning until yearling, and management groups are breeder defined groups. Since many breeders scan at the same time that they take yearling weights, scanning groups are very similarly defined. However, if a breeder weighs some animals but does not scan the animals, then those animals that are scanned will be in a group together for scanning with other animals that have the same yearling group.
Contemporary groups are extremely important in allowing comparisons of animals that are raised the same, and allow the genetic evaluation to remove environmental effects. To be in a contemporary group animals must be the same sex, approximately the same age and managed in the same way. The differences in the performance of animals in the group are what matters in the genetic evaluation, making it important to have several animals in a contemporary group so that these valuable comparisons can be made. Forming proper contemporary groups is extremely important in terms of having an accurate genetic evaluation. In the next article I will discuss how traditional EPDs are calculated and how they can be used.