Udder infection and milk somatic cell count, NAGase activity and milk composition—fat, protein and lactose—in Israeli-Assaf and Awassi sheep

The present study aimed to identify the pathogens that cause subclinical udder infections in Israeli dairy sheep and evaluate their influence on milk yield and composition. Eight hundred and fifteen Israeli-Assaf and Israeli-Awassi dairy sheep were surveyed. More than half of the sheep were in their third or higher lactation (513/815 sheep) and in 14 out of 20 flocks; the sheep were in their peak (second to third month) of lactation. The percentage of bacteriological infected udders in the flocks ranged from 8.6 to 64.3%. The effect of the bacteriological infection on somatic cells count (SCC) was significant (P>0.001). Various species of coagulase-negative staphylococci (CNS) mainly S. chromogenes and S. epidermidis, formed the main pathogen group in infected udders. Lactation number did not significantly influence either the infection rate of udder halves or the milk SCC, although the percentage of udder halves with no bacteriological findings found was higher at first lactation than at the second and third lactation. Milk yield was significantly higher in uninfected than in infected halves. Milk composition—fat, proteins and lactose—varied among flocks, with mean total protein lower in uninfected halves than in infected ones and lactose higher in uninfected than in infected halves.