A contemporary group is a set of animals that have had an equal opportunity to perform: same sex, managed alike, and exposed to the same environmental conditions and feed resources. Contemporary groups are the cornerstone of genetic evaluation. They are the best way to account for environmental effects so that remaining differences among animals may be attributed to genetics, ultimately resulting in expected progeny differences (EPDs).
The responsibility of proper contemporary grouping lies with the individual breeder. Calves born within a 90-day period on the same farm or ranch can be grouped together; however, consideration should always be given to the way the calves are managed and to their nutrition. In many cases, one contemporary group per sex is sufficient. However, differences can exist within the same operation that require the establishment of two or more contemporary groups. Management and group codes may be helpful in these cases.Building Birth Contemporary Groups
Calves of differing sex (bull or heifer) are automatically placed in separate birth contemporary groups.
Birth type is also used to separate calves into birth contemporary groups. Contemporary groups for natural calves are separated by whether the dam is a registered Angus or commercial female. Embryo transfer (ET) calves are not grouped with natural-born calves. ET calves from registered Angus recipient females are assigned to a separate group from ET calves out of other recipient females.
Calves born with-in a 90-day period of one another are placed in the same birth contemporary group.
The birth group code is used to distinguish groups of calves whose mothers were not handled in the same environment before the birth of the calf.
It is important for producers to place individual calves in the correct birth contemporary groups as this group will follow the animals for the entirety of its life. For example, the birth contemporary group criteria will be the first building block to form weaning contemporary groups.
The weaned calf weight date is utilized to separate calves into weaning contemporary groups.
The management code designates whether or not calves were creep-fed or supplied supplemental feeding and separates them accordingly. Code 1 is for non-creep-fed calves, while code 3 is for creep-fed calves.
The group code is used to designate a set of calves managed differently from another set of calves. Calves from different groups or pasture units are designated by using a letter code, such as A, B, C or D. Orphaned or extremely sick calves should be assigned a separate group and not be compared against their normal herdmates.
The yearling weight date is utilized to separate calves into yearling contemporary groups.
Additional group codes may be assigned to distinguish different management cases if necessary. Some breeders create too many contemporary groups, since they may not be aware of the various factors that can split calves into these groups. In other cases, breeders may fail to break a large set of calves into different contemporary groups when the assignment is needed to allow for unequal treatment or an exception.
A typical plan is to take weights and measurements on all calves on the same day and to include as many calves in the contemporary group as possible. Then, the management and group codes can be used to specify known group differences.
Some sample group code applications follow:
Each of the categories above will be a separate contemporary group for comparative purposes as indicated by a different lot identification (Lot ID) in the upper left-hand corner of the Beef Improvement Record "Sire Summary" sheets.
A useful contemporary group size is 10 or more animals of the same sex born within a 90-day period and weighed within a three-day window. For example, calves weighed on Monday, Tuesday and Wednesday can be included in the same group. Calf weaning and yearling weights and ultrasound measures outside the three-day window are assigned to a different contemporary group. It is important to note that sexes are separated in the calculation of interim EPDs and for National Cattle Evaluation (NCE) EPDs. For details on interim EPDs, click here.
Angus contemporary groups are defined at birth. The number of contemporaries either stays the same or becomes fewer as animals are separated from each other for management reasons. Contemporary groups cannot be recombined after herdmates are separated from their defined weaning groups.
Weaning weights, yearling weights and ultrasound measurements are to be taken when animals are within the following age ranges.
Contemporary grouping allows animals to be evaluated on how well they performed compared with their herdmates raised under similar environmental conditions. This grouping accounts for environmental or unequal treatment effects, so that heritable differences, such as EPDs, can be predicted.
Two or more animals of the same sex are necessary in the contemporary group for the EPD to be calculated, assuming other data edits are met. Each animal is compared relative to the average performance of the contemporaries in the defined group. You cannot have EPDs beyond a pedigree index interim EPD without contemporary groups. A contemporary group of one animal does not provide any information to compute EPDs from the Association's NCE.
Example: There are 10 bull calves weaned at your farm or ranch (treated alike, same sex, fed/managed the same). The bulls form one weaning contemporary group. Then, you send two calves to the bull test station and feed out the remaining eight at home. Their yearling and ultrasound records will be processed as two separate contemporary groups, not as one. If you send one bull to a test station, this creates a contemporary group of one for the yearling and ultrasound data. Association ratios for these traits will be 100, and the animal's own yearling and ultrasound performance will not be used in evaluation procedures for EPDs.
A ratio is the performance on an individual animal relative to the average performance for his or her contemporaries. Contemporary groups should include as many animals as can be accurately compared.
Continuing our example, say the 10 bull calves at weaning weighed an average of 600 pounds (lb.). One calf weighed 630 lb., so he is 5% above the average of his contemporaries. His ratio is 105.
Ratio = (630 ÷ 600) x 100 = 105
Another calf weighed 570 lb., which is 5% below the contemporary group average of 600 lb. His ratio is 95.
Ratio = (570 ÷ 600) x 100 = 95
In the calculation of EPDs, the animal's own record (a weight or measure) is used relative to the contemporary group's average performance. It is sometimes a misunderstanding that the numerical ratio (like the ratio computed above) is used in the computations. Ratios can be a within-group tool; however, the use of more advanced selection tools, like EPDs, provides comparisons among all animals in the breed with greater accuracy.