Epidemiology of bovine mastitis in smallholder dairy farms in Unguja Island of Zanzibar, Tanzania

PhD Thesis

Bovine mastitis remains to be the most important disease facing smallholder dairy industry in Zanzibar. Direct and indirect cost incurred during the control of clinical cases of mastitis together with prolonged subclinical mastitis reduces quantity and quality of milk produced, and hence, decrease smallholder dairy farmers’ income. This study was conducted to assess the characteristics and farm management practices of smallholder dairy cattle farming system and their relation with milk production, to quantify the occurrence of subclinical and clinical bovine mastitis and to identify their potential risk factors associated with both forms of the disease. In addition, pathogens causing clinical and subclinical bovine mastitis were isolated and tested for antimicrobial resistance. The study was carried out in three districts of Unguja island of Zanzibar in the United Republic of Tanzania. The selected districts were North B, Central and West districts. Two hundred and three farmers with 425 lactating dairy cows were included in a cross-sectional study that used questionnaire interviews and direct observation to assess characteristics of dairy farming. To quantify the prevalence of subclinical mastitis, questionnaire interviews, direct observations, California mastitis test and laboratory analysis were used. Longitudinal study was used to quantify the occurrence of clinical mastitis. It was found that a dairy farmer possesses an average of seven dairy cattle including two lactating cows. Farmers in West district had bigger average number of lactating cows (3) compared to Central (2) and North B (2), the difference was statistically significant (p<0.05). More than two thirds (72%) of the farmers interviewed kept crossbreed dairy cattle that were managed mostly by zero grazing system (65%). About 61% of the respondents had constructed shed for their dairy animals. About 86% of the farmers provided maize bran, pollard or a mixture of the two as supplement feeds for their lactating cows (p<0.05). Average daily milk production was 7.6 ± 3.6 litres per cow per day. It was found that, average milk production in West district (8.0 litres/day) was higher than average production in Central (7.2 litres/day) and North B (6.9 litres/day), the difference between districts was statistically significant (p<0.05). Two hundred and one farms, 416 dairy cows and 1,648 lactating quarters were tested for the prevalence of bacterial and mycotic subclinical mastitis (SCM). Based on California Mastitis Test (CMT) results, the overall prevalence of SCM was 28.6, 48.8 and 64.7% at quarter, cow and farm level, respectively. Based on bacterial isolation the prevalence was recorded at 42.9, 70.9 and 78.6% at quarter, cow and farm level, respectively. Out of 831 isolates from subclinical cases of bovine mastitis, Staphylococcus aureus composed of 36.8%, Pseudomonas aeruginosa formed 17.8%, Staph epidermidis formed 16.1%, Klebsiella spp. formed 9.5%, Micrococcus spp. formed 6.3% and Escherichia coli formed 4.9%. In addition, it was found that some drugs such as penicillin was no longer appropriate for the treatment of mastitis since 87.6% of isolates were resistant to this drug. The overall prevalence of mycotic subclinical mastitis as defined by mycotic pathogens isolation were 19%, 33.9% and 49.3% at quarter, cow and farm level, respectively. The quarter level prevalence was significantly higher in Central district (26.1%) compared to North B (20.1%) and West (14.4%). The majority of isolated mycotic pathogens were Aspergillus spp (48.2% of isolates), Candida spp (41.1%), and Saccharomyces spp (7.4%). Other minor mycotic pathogens comprised of mucor spp (1.2%), Microsporum spp (0.6%), Prototheca spp (0.6%), Sporobolomyces spp (0.6%) and Trichophyton spp (0.3%). Cow level incidence rate per 100 cow-year at risk, cumulative incidence and cumulative hazard function as reported by farmers were 34.0, 18.3 and 0.27 respectively while those defined by pathogen isolation were 31.8, 17.1 and 0.25, respectively. Quarter level incidence rate per 100 quarters-year at risk, cumulative incidence and cumulative hazard function at quarter level as reported by farmers were 14.5, 7.8 and 0.11 respectively, and those defined by pathogen isolation were 12.9, 7.0 and 0.10, respectively. Out of 212 pathogens isolated from clinical cases of mastitis, major isolates were Staphylococcus aureus (35.4%), Staphylococcus epidermidis (13.7%), Candida spp (8.5%), Pseudomonas aeruginosa (6.6%), Klebsiella spp (6.1%) and Aspergillus spp (4.7%). Risk factors associated with the increased occurrence of subclinical mastitis as defined by CMT screening included herd size and lactation stage. Risk factors for subclinical mastitis as defined by bacteria isolation were dirty drainage, uses of towel to dry udder and number of parity while as defined by mycotic isolation were type of housing and milking technique. The protective factors associated with decreased occurrence of subclinical mastitis as defined by CMT screening included availability of water and uses of calf sucking before milking. The risk factors associated with bacteria isolations were number of milking per day, milking technique, hand wash before milking and amount of milk produced. Risk factors associated with mycotic isolation included number of milking per day and hand wash before milking. Risk factors associated with increased incidence of clinical mastitis as reported by farmers and pathogens isolation included cows’ age and breed, number of parity, lactation stage, milk production, cow hygiene, floor hygiene, study district and calf suckling before milking. Washing hands before milking decreased the occurrence of clinical mastitis. Findings of this study have shown that dairy farming in Unguja Island operates under poor farm management, poor hygiene and improper milking techniques leading to low milk production and increased likelihood of lactating cows being infected with mastitis. Furthermore, the findings revealed high prevalence of subclinical and incidence of clinical mastitis at farms, cows and quarters levels with both contagious and environmental bacterial as well as mycotic pathogens being involved. Findings of this study provide information required to set up strategies to control mastitis in Zanzibar.