Abstract

Klebsiella pneumoniae is a common cause of clinical mastitis in dairy cattle. Wood products are considered to be the main source of Klebsiella on dairy farms. Environmental hygiene and use of inorganic bedding materials such as sand are recommended to control Klebsiella mastitis. However, Klebsiella mastitis still occurs on well-managed dairy farms that use sand as bedding material. In a 5-mo study in a New York State dairy herd performed during the summer of 2005, all of 9 samples of unused sand bedding tested negative for Klebsiella, whereas 14 of 18 samples of used sand bedding contained Klebsiella at a median level of 10(4.6) cfu/g. We hypothesized that fecal shedding of Klebsiella by dairy cows contributes to the presence of Klebsiella in the environment. Using a cheap and simple method based on ampicillin-containing MacConkey agar for screening, and biochemical tests for confirmation of species identity, 595 fecal samples from healthy dairy cattle were screened for presence of Klebsiella. In a longitudinal study of 100 cows followed over 5 mo, more than 80% of fecal samples tested positive for K. pneumoniae. The average prevalence of K. pneumoniae-positive fecal samples was also above 80% in a cross-sectional study of 100 cows from 10 herds across New York and Massachusetts. Fecal shedding of K. pneumoniae by a large proportion of dairy cows may explain why Klebsiella mastitis occurs in herds that use inorganic bedding material or other bedding material that is free from Klebsiella upon introduction into the barn.