Clinical and subclinical mastitis in dairy cattle in Kampala, Uganda

Dairy farming in Uganda provides a source of food, employment and income. Previous studies have revealed high frequencies of bovine mastitis, a costly disease for the dairy farmer. The aims of this study were to investigate the bacteriological panorama in milk from udder quarters with clinical (CM) and subclinical mastitis (SCM) and to determine the antimicrobial susceptibility in staphylococcal isolates. Further, we intended to establish the prevalence of subclinical mastitis and to investigate some environmental factors and animal properties that might influence the frequency of mastitis. For CM, farmers made contact with the members of this study when recognizing an animal with CM. Cows were clinically examined, all quarters were examined by California Mastitis Test (CMT) and milk samples for bacteriological culturing were collected from all quarters positive for CM. A total of 24 milk samples from were collected from 18 animals. For SCM, cows were examined by CMT during afternoon milking and the diagnose of SCM was based on a CMT value ≥ 3 in quarter milk and the prevalence at cow level was determined based on the presence of SCM in at least one udder quarter. Due to practical reasons bacteriological examination of SCM cases was performed only on milk samples with a CMT ≥ 4 (n=166) which were collected from 78 animals. Bacteriological analyses were done locally at Makerere University, Kampala, Uganda and at the Swedish Veterinary Institute (SVA), Uppsala, Sweden. Antimicrobial susceptibility was tested in staphylococcal isolates. Chi test and multi-variable analysis was executed to determine what factors influence the frequency of CM and SCM with a CMT ≥ 4 (SCM-CMT ≥ 4). Of the animals with CM, 22 % were affected in > 1 udder quarter. Concurrent SCM in ≥ 1 quarter was found in 83 % of the animals. At quarter level, 33.5 % of quarters were positive for CM and 47 % of quarters had SCM. The most common pathogen found in CM was coagulase negative staphylococci (CNS) (29 %), followed by Escherichia coli (12.5 %). Of the Staphylococcus (S.) aureus and CNS isolates from CM, 100 % were positive for β-lactamase production. A higher frequency of CM cases was seen in smaller herds, in open grazing systems and in animals with a parity > 1. Subclinical mastitis in ≥ 1 quarter was found in 90 % of the animals that were screened during afternoon milking. At quarter level, the prevalence of SCM was 63 %. The most common pathogen isolated from subclinical mastitis was CNS (12.0 %) followed by Streptococcus agalactiae (8.4 %). Of the S. aureus and CNS isolates 6/7 (86 %) and 16/20 (80 %) were positive for β-lactamase production. A higher frequency of SCM-CMT ≥ 4 cases was seen in zeroand confined grazing systems and in animals with a parity > 1. Zero-grazing systems were correlated to animals in poor hygienic conditions and were more common in smaller herds. Coagulase negative staphylococci, coliforms and S. aureus were more common in CM than in SCMCMT ≥ 4 cases while streptococci were more common among the SCM-CMT ≥ 4 cases. In conclusion, the most common agent found in CM and SCM-CMT ≥ 4 was CNS and a high prevalence of SCM was revealed. The majority of staphylococci were positive for βlactamase production but there was no evidence of methicillin resistant S. aureus. Parity, grazing system and herd size were factors that significantly influenced the frequency of mastitis. It was evident that the milking hygiene procedures were generally poor and probably a contributing factor to the poor udder health. Also, the easy access of pharmaceuticals constitutes a risk in the development of antimicrobial resistance among bacteria.