Abstract

A longitudinal study was undertaken from December 2009 to February 2010 at Hawassa town, Ethiopia, in smallholder dairy farms to identify the role of Staphylococcus aureus and Streptococcus agalactiae in causation of subclinical mastitis and also to assess the role of selected risk factors in the transmission of these pathogens. A total of seven farms were selected. The farms were first screened for subclinical mastitis by California Mastitis Test (CMT) and those free of the disease were monitored. Each farm was visited at intervals of two weeks and during each visit CMT was conducted. A milk sample was aseptically collected from quarters that were CMT positive (a CMT score of greater than or equal to one). Milk samples were cultured, and S. aureus and S. agalactiae were isolated. A cow found positive in CMT in the first test and had S. aureus and S. agalactiae was then excluded and was not subsequently tested and sampled. The average subclinical mastitis incidence rate due to S. aureus and S. agalactiae was found to be 21.84 ± 0.06 Sd per 100 cow- months at risk. Out of 165 CMT positive milk samples cultured for isolation of S. aureus and S. agalactiae, 88 (53.32%) yielded S. aureus and 30 (18.17%) had S. agalactiae. Co-infection by S. aureus and S. agalactiae was found in 14 (8.48%) of CMT positive milk samples. Generally, 104 CMT positive milk samples (63.03%) were due to S. aureus and S. agalactiae. Out of the 12 questions to the milking practice and other contagious mastitis control measures, only two were practiced by all farms: milking mastitic cows last and treating all cases of clinical mastitis. This study reveals that S. aureus and S. agalactiae were the major causes of subclinical mastitis and mastitis control strategies in those farms, and possibly other local dairies which have to focus on these pathogens.

Key words: Contagious mastitis, Hawassa, Subclinical mastitis, Staphylococcus aureus, Streptococcus agalactiae.