Abstract:
A cross-sectional study was conducted from November 2011 to March 2012 on lactating dairy cows to
determine the overall prevalence of bovine mastitis, identify associated risk factors and isolate the
predominant bacterial agents involved in causing mastitis in and around Wolaita Sodo. A total of 349
lactating cows were examined for mastitis using clinical examination and California mastitis test (CMT).
Bacteriological methods were also employed to isolate the causative bacteria. An overall 29.5% (95%
CI: 24.7, 34.3) prevalence of mastitis was recorded in the area of which 2.6% (95% CI: 0.9, 4.3) were
clinical and 26.9% (95% CI: 22.2, 31.6) subclinical cases. About 90 bacterial isolates belonging to 6
species were identified from mastitic milk samples. The isolates based on their relative frequency of
occurrence were Staphylococcus aureus (30%), Streptococcus agalactiae (17.78%), Escherichia coli
(17.78%), Staphylococcus epidermids (13.3%), Corynebacterium bovis (12.2%) and Streptococcus
dysgalactiae (8.9%). The prevalence of mastitis varied significantly (p<0.05) among breeds, where the
highest prevalence was recorded in Jersey (60% (95% CI: 49.3, 70.7)), followed by Holstein-Zebu cross
(30.8% (95% CI: 22.9, 38.7)) and Zebu (10.8% (95% CI: 5.6, 16.0)). It was also appreciated that lactation
stage and parity significantly (p<0.05) influenced the occurrence of mastitis. Animals at early stage of
lactation were severely affected with mastitis than at end and mid lactation stages. The prevalence of
mastitis was found to have a direct relation with parity, as the occurrence of mastitis increased with
parity. Inadequate sanitation of dairy environment and lack of proper attention to health of mammary
gland were important factors (P<0.05) contributing to the prevalence of mastitis. Generally, the study
showed that mastitis is an important problem and a serious threat for dairy industry in the study area.
Therefore, appropriate control measures targeting the specific causative agents should be in place to
reduce the impact of the disease. The farmers should also be aware of the impact of the disease and
practice hygienic milking, culling of chronic mastitis carriers and treating of clinically infected cows.
Key words: Bacterial isolates, bovine mastitis, lactating cow, prevalence, risk factors, Wolaita Sodo
