Prevalence of contagious pathogens of bovine mastitis and use of mastitis control practices
Authors: Sischo William M. , Heider Lawrence E. , Miller Gay Y. , Moore Dale A. 
Published: December 2023

Summary:
A cross-sectional study of 1,032 dairy herds in Ohio was conducted to determine the prevalence of the major contagious pathogens of mastitis (Streptococcus agalactiae and Staphylococcus aureus) and the use of common mastitis control measures.
Herd owners were surveyed by mail concerning their use of mastitis control measures. The survey focused on treatment of nonlactating cows, postmilking teat dipping, culling practices, milking machine maintenance, treatment for clinical mastitis, and premilking hygiene practices. Nearly 90% of questionnaires were returned.
The prevalence of Streptococcus agalactiae and Staphylococcus aureus was determined by use of bulk-tank milk samples. Most herds (n = 802) met the criteria for classification into 1 of 4 groups: (1) Free of contagious pathogens, as determined by inability to isolate coagulase positive staphylococci (cps) and esculin-negative camp positive streptococci (encps) from 3 bulk-tank milk samples, (2) cps, but not encps, isolated from at least 1 sample (3) encps, but not cps, isolated from at least 1 sample, (4) both encps and cps isolated from at least 1 sample. The number of herds in which both encps and cps were isolated was low; therefore, these herds were grouped with herds in which encps alone was isolated for the evaluation of mastitis control practices related to herd pathogen status.
Herd somatic cell count (scc) was determined using Dairy Herd Improvement Association data by calculating the geometric mean scc from individual cow test day scc. Twelve months of scc data from 741 herds were included in this study.
Contagious pathogens were not isolated from bulk-tank milk from most herds, nevertheless cps was isolated from bulk-tank milk from a large proportion of herds (45.4%, 364/802). From the mail survey, it was determined that a high proportion of herd managers teat dipped all cows after milking (90.5%, 838/926) and treated all nonlactating cows (83.8%, 776/926). The other mastitis control practices were not as widely adopted in this group of dairy managers. When the adoption of mastitis control practices were related to the results of the bulk-tank survey, numerous groups of herds could be identified. Group-1 had the highest proportion of herds adopting the surveyed practices, groups 3 and 4 represented the lowest proportion of herds in which all the surveyed practices were adopted, and group 2 had essentially the same profile for adoption of the surveyed practices as group 1. This latter observation in conjunction with the observation that groups 1 and 2 had similar distributions of herd scc suggested that the role of the mastitis control program surveyed in our study may be to control the impact of cps, but it may not be effective in eliminating cps. Another trend was that managers of herds without contagious pathogens were more likely to use a teat dip prior to milking than farms with either contagious pathogen, and this was the 1 management variable that distinguished herds without contagious pathogens from herds with cps.