One of the most important aspects of an accurate genetic evaluation is proper contemporary grouping. Environment and management have a large effect on calf performance. When animals are exposed to variable environments or management practices (feed, pasture, shelter, vaccination, etc.), it is impossible to determine if their differences in performance are due to genetics or environment. Selecting the highest performing animals in this situation is likely to result in selecting animals that had an advantageous environment. Because environment is not inherited, genetic progress is drastically decreased. When every calf is treated as uniformly as possible, the differences between them are more likely to be due to their genetics. In other words, the higher performing animals are more likely to be the genetically superior animals; selecting the genetically superior animal’s results in greater genetic progress. The creation of contemporary groups is the mechanism that allows us to account for management and environmental variation between animals. A contemporary group is a set of same-sex calves that were born within a relatively short window of time and have been managed the same since birth. Each calf in the group has received the same opportunity to express its genetic merit for traits of interest.
If a subset of calves from a group receives different treatment, then those calves should be recoded as a different contemporary group. An example might be a small group of bulls from the larger group sent to a bull test, or perhaps being pulled out to fit for a show. Those bulls should have their data coded with a different contemporary group than the larger group from which they came. Another example might be if a group of calves is large enough that they can’t be weaned/weighed on the same day, they may be broken into separate contemporary groups and weighed on different days. Once animals are separated into a different group, they can never be recombined with the original group.
Every piece of performance data recorded should have the proper contemporary group attached to it. To optimize the amount of information that can be obtained from each performance record, it is best to keep contemporary groups as large as possible while still maintaining equal management and environment for all calves. Single-animal contemporary groups add no information to the genetic evaluation. While keeping contemporary groups as large as possible is useful, every animal must receive equal management. It is better to have 2 smaller groups that are truly managed the same within-group than one large group with unequal management. Improper contemporary grouping can lead to inaccurate and biased genetic evaluations.
In general, ET calves, multiple births, and freemartins are separated into their own contemporary groups. These situations result in different rearing environments for the calf that make it impossible to fairly compare them to other animals. (BIF)
Considerations breeders should be aware of when forming contemporary groups are:
1. Manage calves in groups. Breeders should also manage calves in groups as large as is practical. Within a management group treat all calves alike and weigh them all on the same day with the same scales. Remember, there must be at least two calves in a contemporary group.
2. If possible it’s best if at least two sires are represented within a contemporary group. However, by using the Animal Model when both parents are registered with pedigree this is not an absolute requirement.
3. Make proper use of the weaning and yearling group identification, management and pasture codes. The AWA will use this information too properly for contemporary groups. Cows nursing calves in different pastures should be grouped differently and cows or calves receiving extra attention, such as show cattle, should be grouped separately as well.
4. Follow proper procedures when taking measurements. Guessing, eyeballing or using devices that estimate the measurement are not accurate procedures for genetic evaluation.
5. Be sure to send in all records, even for those calves that you do not intend to register. Sending in pre-selected records will only bias your data and will actually do more harm than good to your better genetics. Complete reporting of records will also assure that cows are given credit for calving and their genetics for reproduction, even for those cows that lost calves prior to weaning.
It is also very important that actual (not adjusted) measurements are submitted to the AWA. Adjustments to a standard age will be computed by the AWA and reported back to the producer. This is to insure that standard adjustment procedures are applied to all cattle in the AWA database.