There is limited epidemiological knowledge on udder health in Kenyan dairy cattle that would aid in a pro-active approach towards mastitis prevention. The study objectives were: (1) to investigate the prevalence and distribution of clinical and subclinical mastitis in dairy cattle in Mukurwe-ini and Nakuru Districts, Kenya, and (2) to determine the antibacterial sensitivity of the organisms causing bovine mastitis in these districts. The study involved field-screening of milk samples from 241 dairy cows on 128 farms by use of the California Mastitis Test (CMT) and, if CMT-positive, followed by bacteriological culture of the major causative agents and their respective antibiotic sensitivity to eight commonly used antibiotics. All participating farms were visited twice during the study period. The results obtained during the first and second visits showed the prevalence of clinical mastitis to be very low: 0.9% and 0.5%, respectively; 56.0% and 65.0% of cows were CMT-positive on at least one quarter and 49.6% and 58.7% of cows were culture-positive, respectively. There was no significant difference in mastitis prevalence between Nakuru and Mukurwe-ini districts (p > 0.10). Staphylococcus aureus was isolated in 68.0% and 77.0% of samples during the first and second visits, respectively. Other frequently isolated agents included Streptococcus agalactiae, and other Streptococcus spp., S. aureus and S. agalactiae were most sensitive to gentamycin and norfloxacin, and least sensitive to cotrimazole and ampicillin. Knowing the prevalence of mastitogenic organisms and their antibiotic sensitivities could improve treatment efficacy and cow longevity.

The study purpose was to validate PetrifilmsTM (3M Microbiology, 2005) against standard culture methods in the diagnosis of bovine mastitis organisms in Kenya. On 128 smallholder dairy cattle farms in Kenya, between June 21, 2010 and August 31, 2010, milk samples from 269 cows that were positive on California Mastitis Test (CMT) were cultured using standard laboratory culture methods and PetrifilmsTM (Aerobic Count and Coliform Count –3M Microbiology, 2005), and results were compared. Staphylococcus aureus was the most common bacterium isolated (73 % of samples). Clinical mastitis was found in only three cows, and there were only two Gram-negative isolates, making it impossible to examine the agreement between the two tests for Gram-negative- or clinical mastitis samples. The observed agreement between the standard culture and PetrifilmTM (3M Microbiology, 2005) results for Gram-positive isolates was 85 %, and there was fair agreement beyond that expected due to chance alone, with a kappa (κ) of 0.38. Using culture results as a gold standard, the PetrifilmsTM had a sensitivity of 90 % for Gram-positive samples and specificity of 51 %. With 87 % of CMT-positive samples resulting in Gram-positive pathogens cultured, there was a positive predictive value of 93 % and a negative predictive value of 43 %. PetrifilmsTM should be considered for culture of mastitis organisms in developing countries, especially when Gram-positive bacteria are expected.