Pathogen identification and incidence rates of clinical mastitis on organic and conventional dairy farms

Thesis objectives were: 1) evaluate incidence rate of producer reported clinical mastitis (IRCM) and predominant pathogen types on conventional and organic dairies; 2) investigate associations between farm type, housing and access to pasture and IRCM; 3) explore association between bulk tank somatic cell count (BTSCC) and IRCM. An investigation on 59 dairy farms in Southern Ontario, Canada, involving organic and conventional management systems was conducted from April 2011 to March 2012. Coagulase-negative staphylococci were the most frequent pathogens (20.4%); Staphylococcus aureus was the most common contagious pathogen (9.6%). The overall mean IRCM was 24.7 cases/100 cow-years. Organic farms tended to have lower IRCM than conventional farms (17.1 cases/100 cow-years vs. 28.1 cases/100 cow-years). In summary, mean IRCM tended to be lower in the organic compared to conventionally managed herds. Housing, pasture use, and BTSCC category were not associated with overall IRCM; however, these factors did impact pathogen-specific IRCM.