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.
- Weaning weights may be taken when the calves are between 120 and 280 days of age.
- Yearling weights may be taken between 320 and 440 days of age. Animals weighed as
yearlings are always grouped in the same manner as they were at weaning. This occurs
for two reasons: First, it accounts for bias due to culling or selection at weaning,
and, second, it accounts for bias due to management and nutrition at weaning. Sexes
are also separated at yearling time.
- Ultrasound measurements are also taken and the animals are grouped from the weaning
contemporary group, with additional breakdowns of the groups for management differences
made at the time of scanning. Ultrasound measurements may be taken in the following
- Bulls - 320 to 440 days of age
- Heifers - 320 to 460 days of age
Contemporary groups, ratios and EPDs
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.