milking unit is removed when milk flow has ceased. Over a 14 week period, the bulk tank SCC dropped from 660,000 to 400,000/mL. This was an outbreak of ...
Alberta Subclinical mastitis associated with Pseudomonas aeruginosa and Serratia marcescens Outbreaks of mastitis caused by Pseudomonas aeruginosa or Serratia marcescens are usually associated with the use of contaminated wash water, teat dips, or multidose mastitis antibiotic preparations (1,2,3). We isolated P. aeruginosa and S. marcescens from 11 and 10 quarters, respectively, in samples collected from cows with subclinical mastitis. Only one quarter yielded both organisms on culture. Samples of wash water and teat dip (although containing other microorganisms) did not yield either P. aeruginosa or S. marcescens on culture. The only intramammary antibiotics used on this farm were individual sterile syringes of dry cow preparations. A disease investigation was conducted on this 85 cow dairy herd which had a bulk tank somatic cell count (SCC) in excess of 600,000/mL. Cows were milked in a double-six herringbone parlor. A hose was used to wash the udder and teats. Following wiping with a sponge dipped in an iodine solution, the milking unit was applied while the teats were dripping. Automatic take-off units were used but the control was set on manual until milking was completed. Many cows were being milked for 12-14 minutes. Overmilking, as well as milking wet udders, resulted in excessive squawking (liner slips). Seventy quarter samples which had a quarter SCC of greater than 100,000/mL were selected for bacteriological study. P. aeruginosa and S. marcescens were isolated from seven and six quarters, respectively, from nine cows. An additional nine quarters from seven cows had a quarter SCC of greater than one million/mL but yielded no significant growth (NSG). When these NSG quarters were resampled 12 and 48 days later, seven more infected quarters were identified. Resampling also confirmed the persistence of these organisms in previously identified quarters. In total, we identified 21 infected quarters from 14 cows. It is interesting to note that five samples yielded no growth on initial culture, but when the samples were replated after incubation and refrigeration, P. aeruginosa was isolated. Although the quarter SCC fluctuated between different sampling periods, 80 percent of the infected quarters had an SCC in excess of one million/mL.
Can Vet J Volume 30, June 1989
Following our initial visit, the owner stopped using the wash hoses in the parlor. A 'dry wipe' with individual paper towels is used on each udder prior to attaching the milking unit. As well, the control for the automatic take-off unit is left on automatic so that the milking unit is removed when milk flow has ceased. Over a 14 week period, the bulk tank SCC dropped from 660,000 to 400,000/mL. This was an outbreak of subclinical environmental mastitis associated with P. aeruginosa and S. marcescens. It appears to have been caused by overmilking as well as milking wet udders.
References 1. Blood DC, Radostits OM, Henderson JA. Veterinary Medicine, 6th ed. London: Bailliere, Tindall, 1983: 479-480. 2. Erskine RJ, Unflat JG, Eberhart RJ, Hutchinson LJ, Hicks CR, Spencer SB. Pseudomonas mastitis: Difficulties in detection and elimination from contaminated wash-water systems. J Am Vet Med Assoc 1987; 191: 811-815. 3. Howell D. Survey on mastitis caused by environmental bacteria. Vet Rec 1972; 90: 654-657.
Gerald Ollis, Matt Schoonderwoerd, Alberta Agriculture, Animal Health Division, P.O. Box 8070, Edmonton, Alberta T6H 4P2.
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