Disease, production and culling in Holstein-Friesian cows III. Disease and production as determinants of disease

Abstract

The effects of the level of milk production and previous disease occurrence (both within the same lactation and in the previous lactation) on the risk of disease occurrence in Holstein-Friesian cows were investigated. The data were from 2875 lactation records from 2008 cows in 32 commercial dairy herds within a 50 mile radius of Guelph, Ontario. Discriminant analysis was applied to data from a subset of 817 cows which completed 2 lactations during the study. This was done in order to simultaneously evaluate the effects of the level of milk production and disease occurrence in 1 lactation, on the risk of disease in a subsequent lactation. Many diseases tended to recur in the second lactation, but the level of milk production was not related significantly to the risk of any of the common disease conditions. A path model, with previous lactation production entered as an exogenous variable, was constructed in order to further evaluate the role of the level of milk production as a determinant of disease. Only milk fever was significantly associated with the level of milk production. Relationships amongst diseases within a lactation were identified by a modified case-control procedure and were used to construct several path models. Relationships amongst diseases in heifers, mature cows and all cows combined are discussed.