April 2021



Bovine anaplasmosis, caused by the hemobacteria Anaplasma marginale (Am) is the most prevalent tick-transmitted disease of cattle worldwide and is associated with significant production losses in cattle. The objective of this survey was to investigate the within-herd seroprevalence of antibodies to Am and the relationship between disease status and milk production after anaplasmosis outbreak in a northern Iowa dairy herd.

Materials and Methods

In 2010 anaplasmosis was diagnosed in an Iowa dairy herd composed of 680 lactating Holstein cows. Samples for serological testing by competitive ELISA were gathered from 799 animals throughout 2011 in 24 separate accessions. Information on milk production, obtained from the DHIA, was gathered from 2010 to 2013. Monthly DHIA milk production was then statistically compared with 2011 anaplasmosis serostatus.

Results and Discussion

Analysis of competitive ELISA data found that 38% of the animals tested positive for bovine anaplasmosis. The DHIA milk data showed seropositive cows produced significantly less milk during 2012 (P = 0.0041) and 2013 (P = 0.0351) than did seronegative animals. This resulted in a mean (±SEM) difference of 1,677 ± 579 kg and 2,175 ± 1,022 kg of milk per cow during 2012 and 2013, respectively.

Implications and Applications

Cows found to be seropositive for Am antibodies produced significantly less milk in subsequent lactations than seronegative cows. Therefore, subclinical anaplasmosis may represent a potential loss of income for dairy producers. Results also suggest that animals should not be assumed free of infection based on geographic location.

Andrew K. Curtis, Johann F. Coetzee