Mild to moderate clinical mastitis: efficacy of intramammary amoxicillin, frequent milk-out, a combined intramammary amoxicillin, and frequent milk-out treatment versus no treatment.

Study objectives were to determine the efficacy of 4 methods (intramammary amoxicillin, frequent milk-out, a combined intramammary amoxicillin and frequent milk-out, and no treatment) of managing mild to moderate clinical mastitis in a university dairy herd. Clinical and microbiological cures, milk production, disease progression, and California Mastitis Tests scores were evaluated. Cows meeting the study criteria were assigned to one of four treatment options based on a systematic randomization scheme (blocked by stage of lactation). Treatments were initiated prior to knowledge of culture results. Cows were observed and evaluated on d 1 to 8, 15, 22, 29, and 36. Overall, treatments were not significantly different than controls. However, when efficacy was evaluated by pathogen group, differences were observed. Intramammary amoxicillin appeared to be the most efficacious treatment for environmental streptococci. Frequent milk-out appeared to be detrimental for environmental streptococci. Treatment method appeared to have little effect on Escherichia coli mastitis, as nearly all cases recovered within a short time frame. None of the treatments were satisfactory for cases of Klebsiella mastitis. When obtained in a timely manner, treatment selection for clinical mastitis should be based on culture results.