Epidemiologic study of intramammary infections with Staphylococcus aureus during a control program in nine commercial dairy herds

Abstract
Objective—To determine the epidemiologic pattern of intramammary infections (IMIs) with Staphylococcus aureus during implementation of a control program in 9 commercial dairy herds. Design—Cohort study. Animals—1,651 lactating cows and 53,098 quarter milk samples. Procedures—Nine herds located in different regions of Italy were enrolled. Control of S aureus infections followed the general principles of contagious mastitis control and was based on precise diagnostic procedures and strict control and segregation of infected cows. All lactating cows in each herd were tested, and those free of S aureus IMI were enrolled as the cohorts. Further additions to the cohort group were cows and heifers free of S aureus IMI, as determined from aseptically collected milk samples taken approximately 7 and 14 days after calving. Results—After the ninth month of the program, incidence decreased to < 2 new IMIs/100 cow-months in 7 of the herds. At the end of the study, 8 of 9 herds had an incidence of ≤ 1 new IMI/100 cow-months. Heifers were most at risk of developing an IMI. Conclusions and Clinical Relevance—Results suggest that control of S aureus IMIs can be achieved by use of a control program based on segregation and use of hygienic and therapeutic protocols. Analysis of incidence and identification of risk factors in a herd could avoid the possible shortcomings of the program, maximizing the probability of success. (J Am Vet Med Assoc 2003;223:684–688)