EVALUATION OF SELECTED ANTIBIOTIC RESIDUE SCREENING-TESTS FOR MILK FROM INDIVIDUAL GOATS

Because somatic cell counts (SCC) of caprine milk are higher than SCC of bovine milk, the performance of antibiotic residue tests for screen ing bovine milk was investigated for caprine milk. Eighty-five does th at were free of antibiotic usage for at least 30 d and that were free of clinical mastitis were sampled at three milkings during a 37-d peri od. At each sampling, foremilk was collected for bacteriological analy sis, and composite bucket milk samples were collected for antibiotic t esting and SCC. Day of lactation, parity, 305-d mature equivalent milk yield, and SCC averaged 221 d (57 to 577 d), 2.3 lactations (one to n ine lactations), 1160 kg (623 to 1750 kg), and 2.2 x 10(6)/ml (0.3 to 30.7 x 10(6)/ml), respectively. The mean Dairy Herd Improvement Associ ation test day milk yield for the month of sample collection was 3 kg (1.4 to 6.4 kg). Intramammary infections were present in 54% of the go ats and in 36% of the udder halves. Assays included positive (5 and 10 ppb of penicillin-G and 50 ppb of ceftiofur) and negative controls th at had been prepared in caprine milk and controls supplied by the manu facturers. One false-negative outcome and one false-positive outcome w ere recorded. For one sampling day, a positive linear relationship exi sted between SCC and the results of one test, and a quadratic relation ship existed between SCC and the results of another test. The antibiot ic residue screening tests for milk from individual goats adequately i dentified milk that was free of antibiotic. These tests are therefore recommended for use with caprine milk.