Faculty Day Faculty of Veterinary Science University of Pretoria 5 September 20 l 3

The purpose of this study was to determine if a particularsomatic cell count (SCC) range can be used as an indicator ofintramammary infection (IMI). Mastitis in dairy cows is mostlycaused by microbial infections and changes in pathogenicitymay be indicated by increased SCC. Cyto-microbiologicalexaminations were performed on 491 464 quarter andcomposite cow milk samples obtained from South Africandairy herds between 2008 and 2012 in the Milk Laboratory atthe Department of Production Animal Studies, Onderstepoort.Data of quarter and composite milk samples with SCCS400 000 cells/ml and S350 000 cells/ml respectively, wereanalysed using the Milk Sample Diagnostic program (MSD)and Microsoft Excell. At the Buiatrics Congress (2012) it was decided by the MastitisSpecialist Committee to adopt a SCC of >200x103 cells/ml asan indicator of intra mammary infection (IMI) in dairy cows. Inthis study, all mastitogenic bacteria isolated from dairy cowsin South Africa were found to be present in milk samples witha SCC of S200x10 cells/ml. In quarter milk samples, (Figure1), 83.17% with no growth, 69.31 % of Staphylococcus aureus(STA), 69.89% coagulase negative staphylococci (CNS),72.45% Staphylococcus pseudintermedius (STI) and 37.23%Streptococcus dysgalactiae (SOY) had a sec S200x103cells/ml. Similar findings in composite milk samples (Figure2) indicated that 88.45% with no growth, 70.17% with STA,74.80% with CNS, 77.61% with STI and 59.54% with SOYhad SCC of S200x103 cells/ml. The highest percentage ofsamples with a SCC of S50x10cells/ml had no growth, whileSOY was the microorganism isolated the least at the sameSCC range. Although CNS is regarded as a minor pathogen,it has been shown to increasingly cause mastitis (Harmon &Langlois 1995 ). As an emerging pathogen in South Africa,STI showed the highest number of isolates found at SCC ofS50x10 cells/ml in both quarter and composite milk samples.Staphylococcus aureus is still isolated in high numbers invarious countries as an important cause of udder infections(Barkema, Schukken & Zadocks 2006). "J4 M•etltog•nlo beot••-1• leolatedfrorn quan•rn1.llk eemplee •t differentsec rans;,o• (~Do ooo c.•fl•lml mllk).