Efficacy of dry-off treatment in sheep

The efficacy of dry-off treatment of sheep in curing chronic intramammary infections and preventing new ones during the dry-off period and during the following lactation was studied in the present work. A total of 85 Israeli-Assaf dairy sheep on one farm in their first, second, third or more lactations were divided into pairs according to bacteriological condition, somatic cell count (SCC), NAGase activity and lactation number, and were then randomly allocated to one of two groups: one group to receive drying-off treatment, the second as an untreated control. At drying off, sheep in the treatment group received intramammary treatment with a commercial cattle dry-off treatment, which is a combination of penicillin, nafcillin and dihydrostreptomycin. At the first sampling (I), 15-20 days after lambing, cure rates (CR) of 64.9 and 6.5% for the treated and control groups, respectively were significantly different (P < 0.001). At the second (II) sampling, 35-50 days after lambing, no change was found in the CR of the control sheep while that of the treated group decreased to 46.4%; this difference was also found to be significant (P < 0.005). New infection rates (NIRs) in the treated and control groups were 15.6 and 28.6%, respectively, at sampling I and 27.3 and 42.9%, respectively, at sampling II. Although the NIRs were lower in the treated group, the difference from the control group was not significant. The new infections were mainly due to different coagulase-negative staphylococci. Overall, in both samplings SCCs and NAGase activities were significantly higher (P < 0.05) in the infected than in the non-infected halves. No significant differences in these parameters were found between treated and control halves that exhibited no infection nor between those found to be infected. However, at sampling II, the mean SCC and NAGase activity in the infected halves were higher in the treated than in the control ones. Antibiotic residues were detected in five of the 25 sheep sampled on the first day, in three out of 25 on the second day and in only in two sheep on the third and fourth days after lambing. On the fifth day no antibiotic residues were detected. These data suggested that dry-off treatment could reduce intramammary infection and somatic cell count of dairy sheep, but other methods are required to both prevent new infection and maintain healthy udders in the herd.