Detection of subclinical mastitis in dromedary camels (Camelus dromedarius) using somatic cell counts and the N-acetyl-β-D-glucosaminidase test

Somatic cell counts, N-acetyl-beta-D-glucosaminidase (NAGase) activity and the infection status of the udder were determined in quarter milk samples (n = 86) from 22 multiparous, clinically healthy camels, traditionally managed by Bedouin nomads in the Negev desert, Israel. Seventy (81.4%) of the 86 samples examined contained bacteria, of which 35 (40.7%) gave mixed isolations of two or more bacteria, suggesting the existence of subclinical mastitis in the camel herds studied. Sixteen samples (18.6%) yielded no growth of bacteria. Staphylococcus aureus, Micrococcus spp., Bacillus spp., Streptococcus dysgalactiae and Escherichia coli were the main organisms isolated. The somatic cell count (SCC) ranged from 1.01x10(5) to 11.78x10(6) cells/ml. NAGase values were between 41.4 and 372 NAGase units. Quarter milk samples that contained bacteria had significantly (p<0.01) higher mean values for SCC but the mean NAGase levels were not significantly different for the bacteriologically negative and positive samples. There was a low correlation coefficient (r(2) = 0.097) between the SCC and NAGase in the quarter milk samples from which bacteria were not isolated (n = 16) and a low negative correlation (r(2) = -0.038) with the samples that contained bacteria (n = 70). The type of bacteria had a significant effect (p<0.01) on the SCC but not on the NAGase activity. Quarter samples from which Staphylococcus aureus (coagulase positive) was isolated showed the highest mean SCC and this organism is therefore suspected to be the underlying cause of the subclinical mastitis. The SCC gave a better indication of the presence of pathogenic microorganisms in milk samples than did NAGase.