Abstract:
Bovine mastitis is a major constraint to dairy production in Sri Lanka, particularly in
dry-zone districts such as Anuradhapura. This study investigated mastitis occurrence,
seasonal variation, and antimicrobial resistance patterns among dairy cattle in
Anuradhapura District from 2023 to 2025. Data were obtained from routine laboratory
records covering all 22 veterinary divisions (n=841). Mastitis was assessed using the
California Mastitis Test (CMT). Seasonal effects were analyzed using binary logistic
regression and chi-square tests, while antimicrobial susceptibility was evaluated using
Fisher’s exact test. Seasonal patterns varied across years. In 2023, cows examined
during the rainy season showed higher odds of CMT positivity than those examined
during the dry season (OR = 2.17; p = 0.63). In 2024, rainy-season cattle exhibited
lower odds of CMT positivity (OR = 0.63; p = 0.065). In contrast, a significant seasonal
effect was observed in 2025, with rainy-season cows having significantly higher odds
of mastitis than dry-season cows (OR = 2.29; p = 0.003). When data from all three years
were combined, rainy-season cattle showed slightly higher odds of mastitis (OR =
1.14), but this association was not statistically significant (p = 0.35). Antimicrobial
susceptibility testing revealed complete resistance to penicillin and amoxicillin across
all samples, indicating widespread ineffectiveness of beta-lactam antibiotics. In
contrast, enrofloxacin and gentamicin showed significantly higher susceptibility
compared to penicillin (p < 0.0001), with no significant difference between the two
drugs (p = 0.054). In conclusion, while rainy-season conditions may increase mastitis
risk in certain years, Overall, season was not significantly associated with mastitis
occurrence. Similar to previous studies, high beta-lactam resistance emphasizes the
need for rational antimicrobial use and evidence-based mastitis control strategies in
Sri Lankan dairy systems.
