Management Alternatives in Mastitis Control and Eradication Programs

Abstract

Herd management programs that are successful in eliminating contagious mastitis include dry cow therapy, segregation and selective culling. When infections involve Streptococcus agalactiae, lactation therapy is still successful although there has been an increase in the number of Strep ag isolates resistant to penicillin and other beta-lactum antibiotics. The major difficulties occur when Staphylococcus aureus is isolated as the primary pathogen in the herd. The primary source of these infections are infected glands and unless these reservoirs are eliminated, new infections will continue to occur. Uninfected cows are mainly exposed during milking but dry cows and prepartum heifers are still at risk when contagious pathogens are present in the lactating herd. Although the method of spread is unknown in nonlactating animals, heifers can become infected before calving with the same strains of organisms as found in the lactating cows.¹ Once Staph aureus infections are eliminated from the lactating animals, the number of infected heifers at calving decreases and often disappears. This is most apparent in herds where Staph aureus has been rapidly eliminated from lactating cows where there is a concurrent rapid decrease in new infections in the heifers at calving. The links speculated as the sources of exposure include insect vectors,² but the reservoir appears to be the adult lactating animal.¹ Because of the spread to young uninfected animals as well as other cows, there is an incentive to try to eliminate these infections from lactating cows. Segregation is an important tool in reducing the risk of exposure at milking, but it does not address other sources of spread. However, many farms cannot create an additional group to segregate infected cows because the group is not the correct size or does not fit well with feeding groups. Likewise, most producers are unwilling to cull infected animals that are producing well and find that the poor response to antibiotic therapy in both lactating and dry cows is frustrating when trying to eliminate Staph aureus from their herds. Since Staph aureus infection can occur anytime during lactation, the longer the lactation and the older the animals, the greater the risk of becoming infected. Thus, herds that have younger cows and a high turnover rate often have a lower prevalence of Staph aureus infected cows, while well established herds with good longevity have greater exposure and accumulate more infections. It is these herds that are trying to retain cows and reach mature production that are often fighting problems with staphylococcal infections. However, no herd is exempt from Staph aureus, even with high turnover, especially if they are purchasing animals.