Each year, the genetic base used to express genetic evaluations in Canada is updated in conjunction with the first official release. The definition of each genetic base used is therefore as follows:
| Breed(s) | Traits | Genetic Base Definition Used |
| All | Production | Cows born during a 3-year period centred seven years ago (2009, 2010 or 2011) that have test day records in the Canadian Test Day Model genetic evaluation analysis. |
| Holstein | Conformation | Proven bulls born in the most recent complete 10-year period (2002 to 2011). |
| Coloured | Conformation | Proven bulls born in the most recent complete 15-year period (1997 to 2011). For Canadienne and Milking Shorthorn breeds, the base period starts with proven bulls born in 1984 and for the Guernsey breed it starts with proven bulls born in 1994. |
The table below indicates the amount of base change realized in 2017 compared to 2016 for each trait and breed. For LPI, the following base adjustments reflect the change to the new scale with half the variance compared to previous years.
