Milk losses associated with mastitis can be attributed to pathogens (direct losses) or to the immune response triggered by infection (indirect losses). The level of infection is often unknown making it difficult to estimate direct losses, whereas indirect losses can be approximated by measuring the association between SCC and milk. An alternative is to perform a mediation analysis. We applied this method on data collected during a survey of clinical mastitis which included milk and SCC, bacteriological cultures, and cow characteristics. Inversely to direct changes, those mediated by SCC were significantly different from zero for all bacterial species. Therefore, we inferred that products to boost the immune system would not sustain milk production and that preventive measures, such as genetic selection for cattle resistant to infection, able to clear an infection with a low SCC, or both, would be more appropriate.

Johann C Detilleux, John P Kastelic, Herman Barkema

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume Genetics of Trait Complexes: Disease resistance, , 092, 2014
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