Discipline: mastitis; Keywords: pathogens, intra-udder infection, TMR and PBS systems, Streptococcus uberis, coagulase negative Staphylococci.

 In recent years, there has been an increase in the prevalence of environmental pathogens as a cause of intra-udder infections (IUI) in dairy cattle. Increases in prevalence could potentially be ascribed to improved control methods for contagious pathogens, difficulties in controlling pathogens from an environmental reservoir and the ability of Streptococcus uberis and Escherichia coli to persist in the udder. The prevalence of mastitis pathogens is changing in South Africa, as fewer than six different pathogens have recently been reported as mastitis - causing pathogens. The objective of the study by the authors referenced below was to use retrospective culture results from composite cow milk samples to estimate and compare the prevalence of mastitis pathogens in different management systems (TMR and pasture-based systems [PBS]) between 2008 and 2013. Furthermore, they estimated the within-herd prevalence for Str. uberis and compared that in the different systems between 2008 and 2013, as it was deemed important to determine whether or not the number of herds that were regarded as Str. uberis - positive were on the rise.

The prevalence of each pathogen, as well as the within-herd prevalence of Str. uberis, were compared between the two years and the two management systems using bacterial culture results from routinely collected composite cow milk samples submitted to the Onderstepoort Milk Laboratory. Coagulase-negative staphylococci had the highest prevalence in both TMR and PBS dairies for both 2008 (29.6% and 26.9%, respectively) and 2013 (20.2% and 22.7%, respectively), which decreased significantly from 2008 to 2013 in both TMR and PBS dairies. Streptococcus uberis showed an increase in prevalence in both TMR and PBS dairies from 2008 (2.36% and 2.63%, respectively) to 2013 (3.10% and 3.64%, respectively). Staphylococcus aureus showed a significant decrease in both TMR and PBS dairies from 2008 (4.71% and 5.62%, respectively) to 2013 (3.95% and 1.71%, respectively). The median within-herd prevalence of Str. uberis for the combined dairy systems showed a significant increase from 2008 (1.72%) to 2013 (3.10%). Statistically significant differences were also found in the prevalence of most of the major contagious and environmental mastitis pathogens between 2008 and 2013 and between TMR and PBS dairies, for example Streptococcus agalactiae. However, this could have been because of localised outbreaks. The within-herd prevalence of Str. uberis increased from 2008 to 2013, with the highest within-herd prevalence in PBS dairies in 2013.  


D. Blignaut, P. Thompson & I-M. Petzer, 2018. Prevalence of mastitis pathogens in South African pasture-based and total mixed ration-based dairies during 2008 and 2013. Onderstepoort Journal of Veterinary Research ISSN: (Online) 2219-0635, (Print) 0030-2465.