Pathogen group-specific risk factors for intra-mammary infection in water buffalo

A cross-sectional study was conducted to estimate the prevalence of intra-mammary infection (IMI) associated bacteria and to identify risk factors for pathogen group-specific IMI in water buffalo in Bangladesh. A California Mastitis Test (CMT) and bacteriological cultures were performed on 1,374 quarter milk samples collected from 763 water buffalo from 244 buffalo farms in nine districts in Bangladesh. Quarter, buffalo, and farm-related data were obtained through questionnaires and visual observations. A total of 618 quarter samples were found to be culture-positive. Non-aureus staphylococci were the predominant IMI-associated bacterial species, and Staphylococcus (S.) chromogenes, S. hyicus, and S. epidermidis were the most common bacteria found. The proportion of non-aureus staphylococci or Mammaliicoccus sciuri (NASM), S. aureus, and other bacterial species identified in the buffalo quarter samples varied between buffalo farms. Therefore, different management practices, buffalo breeding factors, and nutrition were considered and further analyzed when estimating the IMI odds ratio (OR). The odds of IMI by any pathogen (OR: 1.8) or by NASM (OR: 2.2) were high in buffalo herds with poor milking hygiene. Poor cleanliness of the hind quarters had a high odds of IMI caused by any pathogen (OR: 2.0) or NASM (OR: 1.9). Twice daily milking (OR: 3.1) and farms with buffalo purchased from another herd (OR: 2.0) were associated with IMI by any pathogen. Asymmetrical udders were associated with IMI-caused by any bacteria (OR: 1.7). A poor body condition score showed higher odds of IMI by any pathogen (OR: 1.4) or by NASM (OR: 1.7). This study shows that the prevalence of IMI in water buffalo was high and varied between farms. In accordance with the literature, our data highlight that IMI can be partly controlled through better farm management, primarily by improving hygiene, milking management, breeding, and nutrition.

Methods
The data was collected through a face-to-face interview with the farmer, and on-farm observations were taken. During the interview, the farmers gave information on the buffalo source, breed type, and frequency of milking per day. In contrast, animal information, such as body condition score (BCS), udder symmetry, udder shape, type of hand milking procedure, cleanliness of the hind quarter, and milking hygiene, was assessed through on-farm observations by the interviewer. Data analysis was done using R statistical software (version 4.1.2; R Foundation for Statistical Computing, Vienna, Austria). The prevalence of IMI in healthy (CMT = 1) or SCM quarter (CMT ≥ 2) samples was calculated by dividing the number of samples positive for each bacterial species (NASM; S. aureus; Streptococcus; Gram-negative; or other bacteria) by the total number of tested quarter milk samples. The exact binomial method was used to calculate the proportion's 95% confidence intervals. The prevalence of IMI-associated bacterial species was calculated at the quarter, animal, and farm levels. Mixed-effects logistic regression models with animal and farm ID as random effects were constructed to test the association between IMI-associated bacterial species and buffalo or farm-level variables. The significance of the random effect terms was checked using a Likelihood Ratio Test (LRT) using the latent variable approach [24]. Variables for which the univariable P value was < 0.20 were included in the multivariable model. The multivariable model was built using a stepwise forward selection procedure, adding each significant variable in the model, starting with the variable with the lowest P value. Finally, the association of significant (P ≤ 0.05) variables with the outcome was presented in terms of subject-specific odds ratios (OR) and 95% CI.