Higher SCC have been observed in goat milk than in cow milk. This study evaluated the prevalence of high SCC and determined whether increased neutrophils were a factor in high SCC. Bulk tank goat milk samples were collected from commercial dairy goat herds in California, Arkansas, Michigan, and Wisconsin. Total SCC were determined using a Fossomatic Electronic Cell Counter and microscopically using pyronin Y-methyl green stain. Differential counts were determined using Wright's-stained cytospin centrifuge preparations. Average SCC were high (6.12 log10 cells/ml; geometric mean, 1.32 x 10(6) cells/ml). The average of the Fossomatic and direct microscopic SCC indicated that 8.6% of the producers had SCC < .75 x 10(6) cells/ml and that 34.5% were< 1 x 10(6) cells/ml. The current goat milk SCC standard is 1 x 10(6) cells/ml; the cow milk SCC standard will be .75 x 10(6) cells/ml in 1993. Milk samples contained 9.9% macrophages, 2.8% lymphocytes, and 87% neutrophils. These data indicate that high SCC were prevalent and that increased neutrophils contributed to high SCC in the bulk tank goat milk.

Because somatic cell counts (SCC) of caprine milk are higher than SCC of bovine milk, the performance of antibiotic residue tests for screening bovine milk was investigated for caprine milk. Eighty-five does that 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 period. At each sampling, foremilk was collected for bacteriological analysis, and composite bucket milk samples were collected for antibiotic testing 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 nine 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 Association 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 goats 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 that had been prepared in caprine milk and controls supplied by the manufacturers. One false-negative outcome and one false-positive outcome were recorded. For one sampling day, a positive linear relationship existed between SCC and the results of one test, and a quadratic relationship existed between SCC and the results of another test. The antibiotic residue screening tests for milk from individual goats adequately identified milk that was free of antibiotic. These tests are therefore recommended for use with caprine milk.