Persistence of subclinical intramammary pathogens in goats throughout lactation.

The goal of this study was to determine the persistence of caprine intramammary pathogens throughout lactation and to detect the bias in diagnoses when a single milk sample was used. We studied 131 goats throughout 7 mo of lactation. Goats were sampled monthly, and 1834 milk samples were bacteriologically analyzed. One hundred sixty-eight pathogens were isolated: 82.5% were micrococci, 9.5% were Gram-negative bacilli, and 8% were corynebacteria. An intramammary infection (IMI) was considered a true, persistent IMI when the same pathogen was isolated two or more times consecutively from the same half of the udder. One hundred one samples were considered to be truly positive, which produced persistent IMI caused by nine different species (eight Staphylococcus spp. and one Pseudomonas sp.). Statistical relationships were found between staphylococci and true-positive diagnosis and between corynebacteria and false-positive diagnosis. No relationship involving Gram-negative bacilli was detected. A single milk sample had a positive predictive value (60%), high sensitivity (96.2%), high specificity (96.1%), and highly negative predictive value (99.8%).