Prevalence of subclinical mastitis and udder pathogens in small holder dairy farms in Mapepe, Batoka and Choma areas in Zambia

Abstract: Subclinical mastitis (SCM) is a well-known problem in the dairy sector, where it causes severe economic losses mainly due to reduced milk production. This is a problem not only in the western world but also in developing countries. Surveys from different developing countries have shown a SCM prevalence of 52.4 – 88.6 % at cow level and 26.7 – 63.2 % at quarter-level. To combat mastitis is important to optimize the milk production of the cow. The aim of this study was to investigate the prevalence of SCM and udder pathogens on small scale dairy farms in three different areas in southern Zambia, and to obtain information about the distribution of different pathogens and penicillin resistance among staphylococcal species. A field study was conducted including 26 farms. From these farms udder bulk milk samples and quarter milk samples were taken from 111 cows without signs of clinical mastitis (CM). All milk samples were analyzed for somatic cell count (SCC) using the DeLaval cell counter. Bacteriological culturing was done on all quarter samples (n=432). Staphylococcal strains were tested for production of β-lactamase to evaluate the penicillin resistance. Based on SCC > 200 x 103/ml, the prevalence of SCM in the studied cow population was 48.7 % at cow level and 26.9 % at quarter level. The prevalence of intramammary infection (IMI) on cow and quarter level was 41.4 % and 31.5 % respectively. The most common udder pathogens were Coagulase Negative Staphylococci (CNS), followed by Staphylococcus (S.) aureus, accounting for 60.0 % and 30.4 % of the isolated bacteria, respectively. Of the staphylococcal isolates tested for penicillin resistance, 75.9 % of the S. aureus and 34.5 % of the CNS were positive for production of β-lactamase. According to the results, the prevalence of SCM in these areas of southern Zambia is modest compared to reports from other developing countries, both at cow and quarter level, but high compared to countries with a more developed dairy sector. The bacteriological findings are similar to results from other comparable countries, with the exception of the frequency of streptococcal isolates which was low; all together they represented 1.6 %, more than half of which emanated from the same farm. Streptococcus (Strept.) agalactiae, a strict udder bound and contagious pathogen, was only found on one farm which implies that it is not commonly occurring and measures ought to be taken to prevent this bacterium from becoming a growing mastitis problem. Although the prevalence of SCM in this study was not notably high it still indicates that there is a potential for improvement of the udder health to increase the milk production in Zambia. Increasing the level of milk production contributes in turn to better availability of milk which is a wholesome and therefore valuable food item as well as increased income from the sale of milk for the small scale dairy farmer. Achieving improved udder health requires organized control programs with advisory service to the farmers about mastitis prevention as well as resources to implement necessary interventions. Regular surveys monitoring the effects of such programs are needed for success in a long term perspective.