The prevalence, risk factors, antibacterial sensitivity and usefulness or petrifllms as a diagnostic tool for bovine mastitis in Mukurwe-ini and greater Nakuru districts, Kenya

Abstract

An epidemiological study on bovine mastitis was carried out on 241 dairy cows in Mukurwe-ini and greater Nakuru Districts, Kenya, from June 21, 2010 to August 31, 2010. A total of 64 smallholder dairy farms using zero-grazing in the Mukurweini District ofNyeri County, and on an equal number of dairy farms using both zero-grazing and open-grazing in the greater Nakuru District of Nakuru County were selected purposively. The study objectives were: 1) to determine the risk factors and prevalence of mastitis; 2) to determine the antibiotic sensitivity of the pathogens identified; and 3) to determine the usefulness of petri films as a diagnostic tool for determining treatment regimens for pathogens causing mastitis in Kenya. The study involved field screening of quarter milk sample by use of the California Mastitis Test (CMT) followed by aseptic collection of composite milk samples (if more than one quarter tested CMT positive) and there after bacteriological culture (using sheep blood agar, MacConkey agar and_petrifilms) to identify the major causative agents of intramammary infection (lMI) and their, respective antibiotic sensitivity. Questionnaires were used to collect data on animal, management and housing characteristics associated with intramammary infection. All the farms were visited twice during the study period. In the first and second visits the prevalence of clinical mastitis was found to be low 0.9% (2/232) and 0.5% (1/214) respectively. Nine cows were not sampled in the first visit because they were not milking and 27 cows were not sampled in the second visit because they were not sampled in the first visit, some farmers withdrew from the study or cows were dried off or died before the second visit. The results further showed that 56% (130/232) and 65% (139/214) in the first and second visits respectively had intramammary infection on at least one quarter after CMT test. In the first visit mastitis prevalence based on eMT was 51.6% in greater Nakuru District and 61.1% in Mukurwe-ini district. The overall mean mastitis prevalence was 56.03% in both Districts. There was no significant difference on mastitis prevalence between the two districts (x,2 =2.56, P=0.110, relative risk=0.845) while in the second visit, mastitis prevalence was 68,7% in greater Nakuru district and 61.2% in Mukurwe-ini district. The overall mean prevalence was 65.3% in both districts. There was no significant difference on mastitis prevalence between the two districts (X2=1.3, P>0.05, relative risk=1.12). In the first visit, mastitis prevalence based on bacterial culture was 46.8% in greater Nakuru District and 52.8% in Mukurwe-ini district. The overall mean mastitis prevalence was 49.6% in both Districts. There was no significant difference on mastitis prevalence between the two districts (X2 =0.832, P=0.505, relative risk=0.886) while in the second visit mastitis prevalence was 60% in greater Nakuru district and 57.1% in Mukurwe-ini district. The overall mean mastitis prevalence was 58.7% in both districts. There was no significant difference on mastitis prevalence in the two districts (X2=0.178, P>0.05, relative risk=1.05). The study showed that the most frequently isolated causative agent was Staphylococcus aureus at 68% and 77% during the first and second visits respectively. Of the eMT positive samples, 12% and 8% of the samples collected in the first and second visits respectively did not yield any micro-organisms. For the most of the isolated micro-organisms, gentamycin and norfloxacin were the most sensitive antibiotics against the organisms isolated while clotrimazole aI;.d atnpicillin were the least sensitive. Based on eMT as the outcome variable, the risk factors found to be significantly associated with mastitis through logistic linear regression were: whether the cow had mastitis during the current lactation (X2 =7.85, P=0.005), udder washing before milking (X2 =9.81, P=0.007), bedding (X2 =10.48, P=0.043) and depth of manure in the pen where the cow stands when feeding in the manger (X2 =11.06, P=0.026). Based on laboratory bacterial culture as the outcome variable, the risk factors found to be significantly associated with mastitis through logistic linear regression were: whether the cow had mastitis during the current lactation (X2 =2.98, P=0.045), udder washing before milking (X2 =7.54, P=0.023) and depth of manure in the pen where the cow stands when feeding in the manger (X2 =8.96, P'=0.042). Laboratory culture and petri films results showed fair and moderate agreement on results of the first and second visits with a Kappa (K) of 0.306 and 0.457 respectively, with the average sensitivity of 90% and positive predictive value of above 90%. On the total milk samples collected from the first and second visits combined, laboratory culture and petrifilms results showed fair agreement with a Kappa (K) of 0.381, sensitivity of 89.74%, specificity of 51.43%, positive predictive value of 92.51 % and negative predictive value of 42.86%. The results showed that there was high prevalence of subclinical mastitis in Mukurwe-ini and greater Nakuru districts, Kenya. The results also showed that petrifilms can be used for isolation of mastitis causing organisms, and that they are a reliable, easy, rapid and cheap tool for diagnosis and control of mastitis.