The association between the somatic cell count and isolated microorganisms during subclinical mastitis in heifers in Jordan

Mastitis is an important cause of early culling of dairy heifers. The aims of this study were to identify microorganisms that cause subclinical mastitis (SCM) in Holstein heifers in northern Jordan, to estimate the relative importance of various microorganisms, and to examine the correlation between the somatic cell count (SCC) and the isolated microorganisms. Composite milk samples were collected aseptically from 133 Holstein heifers between Days 5 and 14 postpartum for bacterial culture and somatic cell counts. The prevalence of subclinical mastitis in this study was 57.1%. Seventy six (76) of the 133 cows tested had SCC of > 250 000 cells/ml. Bacteria were isolated from 36 (27.1%) cows. About sixty six percent (66.7%) of these isolates were cultured from cows with subclinical mastitis. Coagulase-negative Staphylococci (CNS) were the most prevalent bacteria among isolates (50%), followed by Staphylococcus aureus (22.2%), Corynebacterium bovis and coliforms (E. coli and Klebsiella pneumoniae) (5.6% each), and Streptococcus uberis (2.8%). Interestingly, the majority of the negativeculture samples (53.6%) had elevated SCC. All isolates except for the CNS group exhibited strongly elevated SCC (> 1 × 106cells/ml). However, the coagulase-negative Staphylococci did not have a distinct pattern with respect to SCCs. There was a strong correlation (P ≤ 0.05, correlation coefficient 0.213) between the results of bacterial culture (culture-positive vs. culture-negative) and SCC class but not between SCC class and the type of isolated bacteria. It is concluded that subclinical mastitis appears to be a significant health issue for dairy heifers in Jordan.