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. On 4 central California dairies, 200 Holstein first-lactation cows were randomly assigned to 2 groups. Cows in the treatment group were fitted with an IMD, and cows in the control group were not. The incidence of clinical mastitis for the 2 groups was determined during the study period. Bacteriologic monitoring at intervals over 2 lactations (lactation 2 and through 60 days of lactation 3) was used to determine the incidence of subclinical infection. In addition, data were collected to determine whether the groups differed in milk production, butterfat production, post-milking and test-day somatic cell counts, and reproductive efficiency. Total milk production and butterfat production over the 2 lactation periods did not vary significantly between the groups. Also, the groups did not differ in calving-to-conception interval, duration of lactation, calving interval, and calving-to-first service interval. Cows with IMD were significantly less likely to develop clinical mastitis (5% vs 13%) than control cows. The IMD did not appear to affect subclinical infection rates (minor pathogens only) except at day 300 of lactation 2 and at day 10 of lactation 3, when prevalence was greater 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 coagulase-negative staphylococci infection is short (resolves without intervention).(ABSTRACT TRUNCATED AT 250 WORDS)