Comparison of Culture of Goat Milk with Indirect Measurement of Somatic Cell Count Using a Commercial Kit, and Antimicrobial Susceptibility of Bacterial Isolates

Detection of sub-clinical mastitis in goats is important in the prevention of clinical mastitis, and for the development of treatment protocols. The PortaSCC goat milk test ® (Porta-test) is a novel commercial test for indirect somatic cell count (SCC), and is marketed as a rapid diagnostic method to monitor udder health. The purpose of this study was to compare the results of the Porta-test with culture results, identify bacterial intramammary pathogens in the goats of Grenada, and determine their antibiotic sensitivity. Udder half milk samples from 150 goats in various stages of lactation were evaluated from separate herds on the island state of Grenada. Of 74 udder halves, randomly chosen and studied using the Porta-test, 23 (31%) had normal SCC (category 1), and 51 (69%) had higher SCC, falling in 3 categories of Porta-test positive samples, with 35.2% positives on culture. The differences in culture positivity in the 4 Porta-test SCC categories were statistically not significant. Although indicative of inflammation, the use of this rapid diagnostic method cannot be solely relied upon for the determination of subclinical mastitis of bacterial origin in the caprine. Of the 24 bacterial isolates, 42% were Staphylococcus simulans , and the remaining isolates included one isolate, each of several coagulase-negative species of staphylococci. Of the 24 isolates tested for susceptibility against 12 antimicrobial drugs, only 2 showed resistance, one for penicillin and erythromycin, and one for tetracycline.