EFFECTS OF A HIGH-DENSITY INTRAMAMMARY DEVICE ON MAMMARY-GLANDS, PRODUCTION, AND REPRODUCTIVE-PERFORMANCE IN DAIRY-COWS

A clinical field trial was undertaken to determine the influence of an intramammary device (IMD) on environmental mastitis and production. O n 4 central California dairies, 200 Holstein first-lactation cows were randomly assigned to 2 groups. Cows in the treatment group were fitte d with an IMD, and cows in the control group were not. The incidence o f clinical mastitis for the 2 groups was determined during the study p eriod. Bacteriologic monitoring at intervals over 2 lactations (lactat ion 2 and through 60 days of lactation 3) was used to determine the in cidence of subclinical infection. In addition, data were collected to determine whether the groups differed in milk production, butterfat pr oduction, post-milking and test-day somatic cell counts, and reproduct ive efficiency. Total milk production and butterfat production over th e 2 lactation periods did not vary significantly between the groups. A lso, the groups did not differ in calving-to-conception interval, dura tion of lactation, calving interval, and calving-to-first service inte rval. Cows with IMD were significantly less likely to develop clinical mastitis (5% vs 13%) than control cows. The IMD did not appear to aff ect subclinical infection rates (minor pathogens only) except at day 3 00 of lactation 2 and at day 10 of lactation 3, when prevalence was gr eater in the cows with IMD. The minor pathogens were predominately (80 %) coagulase-negative staphylococci. It was unusual to have coagulase- negative staphylococci in the same quarter at 2 consecutive samplings, prompting the speculation that during lactation, the duration of coag ulase-negative staphylococci infection is short (resolves without inte rvention). However, new infections developed in other quarters, thus m aintaining a consistent quarter prevalence throughout the lactation. T he IMD induced a significant increase in postmilking somatic cell coun t, compared with results from control cows, and test-day somatic cell count had a more modest increase in cows with IMD, compared with previ ous studies.