THE INCIDENCE OF SUBCLINICAL MASTITIS AND RELATED PATHOGENS IN TWO LINES OF DAIRY CATTLE

Abstract

The California Mstitis Test (CMT) was done on 6609 and 4206 quarter samples from Holstein and synthetic Ayrshire based lines of cows, respectively to study the effects of line, parity, month of freshening, and month of lactation. CMT scores for individual quarters were coded from 1 to 5 and transformed to log scale to normalize the distribution. Individual quarters were considered positive if they scored either CMT2 or CMT3. A cow was considered positive if one or more of her quarters were positive. The incidence of subclinical mastitis as judged by CMT score was similar in both lines, and older cows were much more apt to be positive to the mastitis-screening test than younger cows. The incidence of positive quarters was higher for the cows calving during summer months, and there was an increase in the CMT score in the later months of the lactation period. Microorganisms were isolated from 21.5, 31.5, 42.3, and 53.0% of the samples showing a CMT reaction of trace, 1, 2, and 3, respectively. Klebsiella was found in 40.5% of the samples and Streptococcus was isolated in 36.8% of the samples. Other organisms isolated were Staphylococcus aureus (14.9%), and coliform (6.4%).