Bovine mastitis: Risk factors and isolation of Gram-negative bacteria in Western Algeria

A cross-sectional study was conducted in western Algeria between February and October 2024, aimed at determining the prevalence of bovine mastitis, Gram-negative bacilli, and their associated risk factors. A total of 524 cows were sampled using clinical examination and the California mastitis test. Milk samples from the affected quarter were subjected to bacteriological assays. Three generalised linear mixed models were used to identify the risk factors for clinical mastitis (CM) and subclinical mastitis (SCM), as well as Gram-negative bacilli isolates associated with bovine mastitis. Model selection was performed using the Akaike information criterion. The prevalence of mastitis was 59.7% at the cow level, of which 12.6% was CM and 47.14% SCM. Overall, 65.5% of the mastitis cows showed a positive culture for Gram-negative bacilli. The most commonly isolated bacteria were <i>Escherichia</i> spp. (44%), <i>Klebsiella</i> spp. (23.1%), and <i>Pseudomonas</i> spp. (11.6%). The parity, contact with visitors, and daily milk yield (l/day) were identified as risk factors for SCM in dairy cows. However, foremilk discarding reduced the risk of developing SCM. A history of mastitis, udder injuries, udder and leg hygiene scores, and parity were identified as risk factors for CM. Nevertheless, none of the variables examined were risk factors for an udder infection by the Gram-negative bacilli isolates.