Collaborative evaluation of rolling ball viscometer for measuring somatic cells in abnormal milk

The Ruakura rolling ball viscometer was evaluated in 3 laboratories along with currently approved instrumental methods for measuring somatic cells in milk and the Wisconsin mastitis test. Replacement of the Teepol reagent with Wisconsin mastitis test reagent in the rolling ball viscometer was also evaluated. Both repeatability and reproducibility were satisfactory for all methods evaluated. The instrumental methods each gave higher readings than the other 3 methods. Use of Wisconsin mastitis test reagent in the rolling ball viscometer improved both repeatability and reproducibility. Additional work on standardization is suggested to match rolling ball viscometer readings with those of the instrumental methods.