Removal risks in Swedish Friesian dairy cows according to parity, stage of lactation, and occurrence of clinical mastitis.

The removal risk of Swedish Friesian dairy cows was analysed. The risk of removal increased with parity, and first parity cows were removed earlier in lactation than cows of higher parities. A positive report of clinical mastitis increased the risk of removal, both in the month of developing mastitis and during subsequent part of lactation. The consequences of different removal pattern for epidemiologic analyses of observational studies are discussed.