Accelerated lambing systems (ALS) are popular in Canada, but their effect on udder health has not been well described. In this prospective study of one flock of ewes (n = 153), bacteria were cultured from the milk of 84% of ewes at lambing, 74% at mid-lactation and 77% at weaning. Coagulase-negative staphylococci predominated. However, 7-10% of ewes had intramammary infections (IMI) with major pathogens. The California Mastitis test (CMT) and somatic cell counts (SCC) in comparison with bacterial culture, showed low sensitivity (CMT −≤ 43%, SCC: ≤ 62%) and high specificity ($\ge$95%). Efficacy of dry therapy was evaluated. Treatment did not prevent IMI by any pathogen as measured by bacterial culture, but it cured IMI caused by major pathogens. This study also examined risk factors for IMI; elevated SCC, and their relationship with lamb growth. Elevated SCC had significant negative effect on average 50-day lamb weight.