ABSTRACT
The objective of the present study was to compare the efficacy of conventional and extended intrammamary [IMM] therapy of persistent subclinical mastitis in lactating dairy cattle using nafcillin-penicillin-dihydrostreptomycin combination [NPD]. Sixty-five dairy cows with 126 infected quarters were enrolled in the study. Infected cows were allocated randomly to 1 of 3 different treatment regimens: [1] conventional group: NPD administered IMM 3 times at 24-h intervals [20 infected cows, 43 intramammary infections [IMI]], [2] extended group: NPD administered IMM 6 times at 24-h intervals [23 cows, 43 IMI], and [3] untreated control group [22 cows, 40 IMI]. The overall bacteriological cure [BC] rates for subclinical IMI were 86.04%, 100%, and 20% for the conventional, extended and the control groups, respectively; indicating a higher BC rate [P<0.0001] for the treated groups than the control group. Significant difference [P=0.029] concerning the BC rate was also observed between the extended and the conventional groups. Significant difference [P=0.0021] in somatic cell count [SCC] was detected between the extended and the conventional groups. Significant difference [P=0.0021] in somatic cell count [SCC] was detected between the extended and the control group. Fat percentage increased in the conventional [P=0.029] and in the extended [P<0.0001] groups, and protein percentage increased only in the extended group [P=0.0016]. There was no significant difference in posttreatment milk production between the groups [P>0.05]. Results of this study indicate that NPD therapy was effective in eliminating subclinical IMI in lactating dairy cows, and that extended therapy enhanced BC rate and reduced SCC