Seasonality of the conjunctival microbiota in cattle from a microregion in midwestern Brazil

This study aimed to identify the bacterial and fungal organisms in the conjunctival fornix of healthy cattle in a microregion located in midwestern Brazil. Additionally, we evaluated whether seasonality and cattle category (dairy vs. beef) play a role in our findings. The conjunctival fornix of 74 Holstein x Gyr and 70 Nelore cattle were sampled from February to March (rainy season) and August to September (dry season) of 2017. Bacterial and fungal strains were isolated by classical bacteriological and mycological methods. Some bacterial species were also identified by polymerase chain reaction. From the 144 animals included in the study, a total of 12 bacterial genera were identified, with Bacillus cereus being the most prevalent agent in both seasons and cattle categories. The total number of bacteria was not influenced by seasonality or cattle category (P = 0.25). The number of Moraxella bovoculi identified in dairy (5/74) and beef cattle (7/70) did not differ statistically (P = 0.76). However, seasonality played a role in M. bovoculi identification, being found only during the rainy season in the dairy cattle (P = 0.01), and only during the dry season in the beef cattle (P = 0.04). During the dry season, the number of gram-positive bacteria was significantly higher than the number of gram-negative bacteria in beef cattle (P = 0.009). Fungi were isolated in 20/144 samples. The number of fungi isolated in dairy cattle (16/144) was significantly higher than that isolated in beef cattle (4/144) (P = 0.007). Although a higher number of fungi were isolated in both cattle categories during the rainy season, this finding was not significant (P = 0.53). In this microregion located in midwestern Brazil, Bacillus cereus was the most prevalent and Corynebacterium spp. and Streptococcus spp. the least prevalent bacteria found in the conjunctival fornix of healthy cattle. The prevalence of the conjunctival fungal microbiota (11.8%) was lower than previously reported, with a higher number of isolates found in dairy cattle. Trichosporon spp. (41.2%) and Aspergillus spp. (35.3%) were the most frequent genera, being most commonly isolated in the rainy season.