Base Change Summary – April 2026
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 (2018, 2019 or 2020) that have test day records in the Canadian Test Day Model genetic evaluation analysis. The same base group is also used for Pro$. |
| Holstein | Conformation | Proven bulls born in the most recent complete 10-year period (2011 to 2020). |
| Coloured | Conformation | Proven bulls born in the most recent complete 15-year period (2006 to 2020). 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 2026 compared to 2025 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.
Base Changes for 2026 Versus 2025
| AY | BS | CN | GU | HO | JE | MS | |
| LPI1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| Milk (kg) | 83 | 31 | 26 | -31 | 82 | 63 | 20 |
| Fat (kg) | 3.9 | 1.1 | 0.4 | -0.1 | 7.0 | 3.8 | 0.8 |
| Protein (kg) | 3.6 | 1.4 | 0.5 | 0.0 | 5.0 | 2.8 | 0.9 |
| Conformation3 | 0.69 | 0.14 | -0.02 | 0.18 | 0.59 | 0.16 | -0.01 |
| Mammary System3 | 0.61 | 0.29 | 0.00 | 0.10 | 0.61 | 0.19 | -0.04 |
| Feet & Legs3 | 0.61 | -0.11 | -0.09 | 0.18 | 0.42 | 0.10 | 0.03 |
| Dairy Strength3 | 0.50 | -0.16 | 0.01 | 0.10 | 0.25 | 0.06 | -0.05 |
| Rump3 | 0.27 | 0.26 | 0.06 | 0.15 | 0.14 | 0.00 | 0.10 |
| Herd Life2 | 0.23 | 0.41 | 0.02 | 0.18 | 0.42 | 0.19 | 0.00 |
| Somatic Cell Score2 | 0.14 | 0.26 | 0.14 | 0.47 | 0.41 | 0.15 | 0.23 |
| Daughter Fertility2 | -0.30 | 0.14 | 0.02 | 0.26 | 0.30 | 0.16 | -0.03 |
1 – Base change for LPI is set to zero since it is already reflected by the change in the “Constant” included in the LPI formula.
2 – Traits expressed on scale of Relative Breeding Values (RBV).
3 – The base change for Conformation traits are based on genetic evaluations calculated using daughter classifications and not composite indexes as introduced in April 2021
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