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 animals results in greater genetic progress. The creation of contemporary groups is the mechanism that allows us to account for management and environmental differences 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.
Contemporary Grouping Components by Trait
Please refer to each specific trait's page for more details. You can navigate to them from the traits page which has a list of traits and links to their specific description article.
Calving ease and birth weight: Breeder herd code, Year, Season, Sex, Management code, ET or not
Weaning weight: Calving ease/birth weight contemporary group criteria, Management code (include pasture), Weigh date, Weaning sex
Yearling weight: Weaning weight contemporary group criteria, Management code, Weight date, Yearling sex
Ultrasound traits: Yearling weight contemporary group criteria, Management code (if different than yearling management), Scan date
Carcass traits: Yearling contemporary group criteria, Management code (if different than yearling management), On feed date, Harvest date, Days on feed, Grading date, Carcass sex, Breed of dam
Heifer pregnancy: Yearling weight contemporary group criteria, Breeding management code, Breeding season start and end dates, Exposure, Breeding pasture/sire
Mature cow weight, height, and body condition score: Breeder herd code, Year, Date measured, Cow age at measurement, Birth management code
Stayability: Breeder herd code, Birth year, Herd code in which cow produced a calf
Feed Efficiency: Yearling contemporary group criteria, Feed efficiency management code, Date on feed, Scan or harvest date, Sex
Depending on the type of evaluation (single breed, multi-breed, animal model, sire model), breed composition of the calf or dam may be part of the contemporary group definition.