Dutch national mastitis survey. The effect of herd and animal factors on somatic cell count

The purpose of the national mastitis survey was to collect information on the prevalence and causes of bovine subclinical mastitis in the Netherlands. Milk samples were collected once from 10 336 cows in a stratified random selection of herds (n = 227) in the Netherlands during the years 1985-1986. Results showed that 84.2 % of the cows were free from mastitis. Ten per cent of all udder quarters were infected, and 3.7 % of these were infected with Staphy(ococcus aureus, the main udder pathogen. Statistical analysis based on a 'split-plot' model was used to analyse the effect of herd factors and animal factors on somatic cell counts (SCC). Several factors significantly influenced SCC: breed, season, geographical region, type of housing, and the use of teat disinfection. The effect of herd and animal factors on SCC of milk samples of individual cows was calculated as deviation from the geometric mean cell count of the standard cow (222 000/ml) and presented as the excpected SCC per cow. The interaction of parity x stage of lactation x infection status also significantly influenced SCC. On the basis of expected SCC of uninfected cows correction factors were calculated for individual cows with various parities and at various stages of lactation. We conclude that the use of these correction factors can improve the analysis of SCC in the diagnosis of mastitis