Dairy farmers must often deal with high-producing cows that are chronically infected in an udder quarter that does not respond to antibiotic therapy. Such quarters contribute to elevated somatic cell counts (SCC) and bacteria counts in herd milk, and serve as reservoirs for infecting other cows. However, these quarters can be dried off and converted to a nonfunctional state without harming adjacent quarters. Production of high quality milk with low SCC yields a premium from many milk plants and dairy cooperatives. Thus, dairy farmers should make every effort to reduce the SCC of herd milk to the lowest possible level.
In a university study, 15 lactating Jersey cows chronically infected with Nocardia species, Pseudomonas aeruginosa, Escherichia coli, or Serratia species were studied. All infections had been refractory to repeated attempts of antibiotic therapy and had elevated SCC (millions/ml). The purpose of the investigation was to determine if infected quarters could be dried off and rid of their existing infections. Infected quarters were infused after milking with 60 ml of Nolvasan® (2% solution of chlorhexidine diacetate) under the supervision of the herd veterinarian, milked out and dumped at the next milking, and reinfused at 24 hours after the first infusion. All milking of the treated quarters was discontinued after the second infusion. Bacteriological status and SCC were determined before infusion and at regular intervals until each cow entered her nonlactating period. Residue testing was performed on quarters from which secretion could be obtained using the Delvotest®. Quarter SCC were performed using a Fossomatic 90 electronic cell counter, and milk yield was obtained from Dairy Herd Improvement records. Rectal temperatures were taken one time at 24 hours after the first infusion. Six of the 15 cows were later sacrificed and mammary tissue collected for histologic analysis.
Results and Discussion
All quarters infused with Nolvasan® were permanently rendered nonfunctional 14 to 63 days after the first infusion. Somatic cell counts in treated quarters decreased from 8,622 x 103/ml before infusion to a mean of 4,914 x 103/ml over the 2 months after infusion (Figure 1), and decreased to approximately 1,000 x 103/ml by day 63 post infusion (Figure 2). In uninfused, uninfected adjacent quarters, SCC increased from 247 x 103/ml before infusion to an average of 317 x 103/ml over the 2 months after infusion (Figure 3).
Infused quarters were sensitive upon palpation by 24 hours post treatment, and swelling was apparent in 2 quarters of the 15 cows, but symptoms disappeared after the first week. Secretions from infused quarters exhibited large clots and a watery consistency. Fluid volume decreased with time, and no secretions were obtained at 63 day post infusion. Body temperatures taken 24 hours after the first infusion were normal (101.6°F).