Breeding Cattle for Mastitis Resistance

The development of an immunological assay where cells isolated from blood are stimulated by an Staphylococcus aureus antigen in vitro is described. Variation was observed in the ability of cells isolated from young cattle, cows and bulls to respond in vitro to S. aureus, suggesting that differences in immune responsiveness may be measured by this method. Bull progeny groups were shown to have cells with significantly different abilities to respond in the assay. There was a significant negative correlation between the immune response of bulls and their predicted transmitting ability (PTA) for somatic cell count (SCC). In other words, bulls that were high responders in the immune assay tended to have daughters with lower SCC, while bulls that were low responders in the immune assay tended to have daughters with higher SCC. The assay, therefore, shows potential for use as an indicator for selection of bulls whose progeny might be relatively resistant to sub-clinical mastitis caused by S. aureus. The approach currently being used to identify genes that may be important in controlling mastitis resistance and some preliminary immunological results relating to mastitis are also described.