Udder disease etiology, milk somatic cell counts and NAGase activity in Israeli Assaf sheep throughout lactation

Bacterial pathogens causing udder infections in Israeli Assaf dairy sheep w ere identified and changes occurring throughout lactation were monitored to study the correlation between the contaminant and the severity of the infe ction, as measured by somatic cell count (SCC) and NAGase tests. A total of 159 Israeli Assaf dairy sheep on one farm, in their first (69), second (13 ) or third and more (77) lactations were included in this study. Udder halv es were tested for bacterial condition, SCC and NAGase activity 2-3 weeks p ost lambing and every 4 weeks after until drying-off. At first sampling, in 60.7% (193/318 quarters) of the halves no bacterial growth (NBG) was detec ted. Different species of coagulase negative staphylococci (CNS) were the m ain pathogen group in infected udders. Streptococci were isolated from 14 h alves, most of them in the two udder halves. The percent of udder infection in sheep in their third or further lactations was 2.8 greater (P < 0.05) t han in that of sheep in their first lactation. During the lactation, 90.6% of the halves did not change their classification status, suggesting that m ost infections occur before lambing and/or during the following first few d ays. Thr arithmetic mean of SCC and NAGase of total half udder milk and sam plings (during the lactation) were 1144 +/- 48 x 10(3) cells/ml and 49.4 +/ - 2.5, respectively. The average SCC in the milk of halves classified as NB G was 321 +/- 35 x 10(3) cells/ml and was not significantly changed during the lactation period. In halves infected with CNS, average SCC was 1371 +/- 150 x 10(3) cells/ml at the first testing and increased to 2129 +/- 347 x 10(3) cells/ml at drying-off. No significant differences were found in SCC and NAGase activity between the different species of the CNS. The mean SCC over the types of bacteria isolated, lactation number and days in lactation was significantly different (P < 0.0001). In 4% of the halves, from all sa mples, SCC was above 5000 x 10(3) cells/ml although no bacteria were detect ed in their milk. The higher SCC in the CNS infected halves contrasted with the more moderate SCC found in dairy cows similarly infected, suggesting t hat the sheep udder has a lower resistance and an augmented immunological r esponse against this group of bacteria. Thus. this should be considered acc ordingly in schemes for sheep's milk quality payment. (C) 2001 Elsevier Sci ence B.V. All rights reserved.