Mastitis is the most common, expensive and detrimental disease of dairy cattle. Mastitis in heifers around calving threatens udder health in the first and consecutive lactation, increases the risk of premature culling, and leads to economic losses. Together with enhanced preventive management practices, genetic selection for heifer mastitis resistance could aid in a more efficient and sustainable way. Although good progress has been made in comprehension of genetics of mastitis resistance, knowledge of genetic variation of pathogen-specific heifer mastitis is still very limited. Moreover, little genetic research has been conducted on heifer mastitis focusing on the period around first calving and also on pathogen-specific occurrence. Despite the low heritability of clinical mastitis, studies have shown that there is exploitable large genetic variation among bulls. The objective of this study is to investigate genetic variation of overall and pathogen-specific heifer mastitis in Canadian dairy herds. Data collected over a 2-year period as part of National Cohort of Dairy Farms of Canadian Bovine Mastitis and Milk Quality Research Network (CBMQRN) from 91 Canadian dairy herds spread over 6 provinces will be used for the study. Incidence of overall and pathogen-specific clinical mastitis will be treated as 0, 1 and > 1 cases of clinical mastitis. A generalized linear mixed model will be used for the estimation of variance components. Estimated genetic parameters from this research will provide insight into genetic variation of heifers associated with mastitis in Canadian dairy herds. Results will be ready to be presented at the conference.