MASTITIS RESEARCH IN SA: LABORATORY TESTS AND OTHER METHODS.

Discipline: mastitis; Keywords: CMCT, udder health, composite milk samples, SCC, teat end vacuum, bulk tank testing, psygrotrophic and thermoduric bacteria.   

Laboratory diagnosis of mastitis can be costly and time consuming, therefore cow-side tests such as the California Milk Cell Test (CMCT) and Milk Electrical Resistance (MER) need to be utilised to full potential. It has been estimated that financial benefit of correct diagnosis of mastitis per cow for the CMCT, MER and the tests done in parallel was R899, R519 and R1065 respectively. The CMCT was shown to be 11% more beneficial than the MER test, whilst using the tests in parallel was shown to be the most beneficial method for evaluating the mastitis-control programme. Therefore, it is recommended that the combined tests should be used strategically in practice to monitor udder health and promote a pro-active udder health approach when dealing with host-adapted pathogens.

Quarter milk samples for routine udder health herd examination have been replaced by composite milk samples because of practical and financial reasons. In composite samples, milk from the four udder quarters is combined, with a consequent dilution effect that has required different interpretation of the results from quarter milk samples. The objective of a study was to establish a SCC threshold to predict the presence of udder infection in composite milk samples and to compare the results with those in quarter milk samples. Udder infection at SCC thresholds of 150 000 cells per mℓ and 200 000 cells per mℓ differed only by 3.26% in composite milk samples. In a statistical model, the optimum SCC thresholds for composite and quarter milk samples was subsequently estimated to be 150 000 cells per mℓ and 200 000 cells per mℓ, respectively.

The preservation of the teat canal is crucial for udder health, as the main route for bacterial infection is via the teat canal. Milking machines differ in layout and settings and continue to be a challenge to the primary immune system of the bovine udder namely the teat canal. Different levels of teat end vacuum during machine milking may influence milking performance and teat condition. In a preliminary investigation, it was found that even in a milking system where the automated cluster removal settings have a short reactive time (short milk tube and a flow meter lower than the level of the udder) the take-off time overall could be improved.

Routine bulk tank milk testing is an adjunct to monitoring milk quality and udder health as total bacterial counts, and enumerating psychrotropic and thermoduric bacteria counts, may provide useful information on the cleanliness of milking procedures and equipment, the effectiveness of milk cooling and system sanitation. Also, differential bacterial counts may provide information on the occurrence of and changes in mastitis pathogens. In a study on several herds, vast differences in overall milk quality were evident between herds with bulk tank SCC, ranging from 145,000 cells per mℓ to 730,000 cells per mℓ and total bacterial counts from 5,240 cfu’s per mℓ to 55,460 cfu’s per mℓ. High psychrophile counts in bulk tank samples were common in all herds. In one herd, this was largely attributable to the high incidence of sub-clinical mastitis caused by environmental streptococci. In other herds, the problem seemed multi-factorial, influenced by inadequate pre-milking practices in two herds, problems with cleaning of equipment in one and inadequate cooling of milk in another. The results clearly are cause for concern. However, in the context of the purpose of the study, the use of bulk tank milk analysis as an adjunct to existing udder health monitoring tools should be valuable in the quest to produce milk of the highest quality.

Reference:

Meissner, H.H., 2021. Summary of Research Progress with Mastitis 2015 to 2021. Report to Milk SA Board, November 2021, Milk SA, Pretoria.