Effect of parity in age adjustment factors in the Italian Holstein Friesian cattle breed

Inclusion of parity in multiplicative adjustment factors for age at calving was investigated for the Italian Holstein Friesian cattle breed. Separated age adjustment factors for first, second, third and later parities are necessary because cows of the same age but different parity have different production. Differences in production were particularly evident for first and second parity cows of same age. If parity is not accounted for, first lactation mature equivalent production can be underestimated. Because progeny testing is based on first lactation production, underestimation of a fraction of mature equivalent records may be reflected in genetic indexes.