Efficacy of the selective treatment of clinical mastitis based on on-farm culture results

The objective of this clinical trial was to evaluate the efficacy of using on-farm culture to guide strategic treatment decisions in cows with clinical mastitis. A total of 422 cows affected with mild or moderate clinical mastitis in 449 quarters were randomly assigned to either a) a positive-control or b) an on-farm culture-based treatment group. Quarter cases assigned to the positive-control group received immediate on-label intramammary treatment with cephapirin sodium. Quarters assigned to the culture-based treatment group were treated with cephapirin sodium if incubation of milk using an on-far culture system for 18-24 hours showed Grampositive growth or a mixed infection. The proportion of quarters that received intramammary antibiotic therapy because of study assignment or secondary (or extended) therapy was 100% and 51% for positive-control and culture-based groups, respectively. There was a tendency for a reduction in days in which milk was discarded from cows assigned to culture-based group vs. positive-control group (5.9 vs. 5.2 days). There was no difference between cases assigned to the positive-control vs. culture-based group for days to a clinical cure (2.7 vs. 3.2 days), bacteriological cure risk (71 vs. 60%) and risk for a new intramammary infection within 21 days of enrollment (50 vs. 50%). There was no difference in the risk and days for recurrence of a clinical mastitis event in the same quarter (35% and 78 days vs. 43% and 82 days), linear somatic cell count (4.2 vs. 4.4), daily milk production (30.0 vs. 30.7 kg), and risk and days for culling or death events (28% and 160 days vs. 32% and 137 days) for the rest of the lactation. In summary, the use of on-farm culture to guide the strategic treatment of clinical mastitis reduced intramammary antibiotic use by half and tended to reduce withholding time by one day, without affecting short or long-term health or production outcomes.