Characteristics of non-clinical mammary infections of goats.

This study, carried out on 1217 milk goats (2428 milk samples), sampled at two different periods of lactation, showed that non-clinical mammary infections of the goat were due to major pathogens (7.5%) and coagulase-negative staphylococci (24.1%). Among major pathogens, Staphylococcus aureus was the most frequently isolated species (75.2%). However, great variations were observed between herds, in levels of infection by major pathogens. The intensity of the inflammatory response, measured by the cell count, depended on the pathogen present in the mammary gland. Evidence was found that 75% of infections persisted throughout the lactation and 61% during the dry-period. The arithmetic mean cell counts for milk samples from halves infected with major pathogens was 6.77 X 10(6) cells/ml, determined by Coulter Counter. It was 1.78 and 1.54 X 10(6) cells/ml respectively for halves infected with coagulase-negative staphylococci and non-infected halves. The arithmetic mean cell counts were higher at drying-off than in lactation. The threshold of 1 X 10(6) cells/ml was reliable for diagnosis in mid-lactation and permitted to diagnose 72% of major pathogen infections.