A clinical trial to evaluate the effectiveness of antibiotic treatment of lactating cows with high somatic cell counts in their milk.
OBJECTIVE
To determine the effectiveness of treatment of lactating cows with high somatic cell counts in milk.


METHODS
Randomised clinical trial.


METHODS
Single pooled quarter samples of milk were obtained from cows with somatic cell counts above 500,000 cells/mL on fifty farms. Milk samples were cultured for known mastitis bacterial pathogens. Cows were randomly allocated to treated and untreated groups. Treated cows received both intramammary cloxacillin and parenteral erythromycin. Single pooled quarter milk samples were obtained at 6 weeks after treatment and were cultured for the presence of pathogenic bacteria. The percentage of samples with no growth at the post-treatment culture was used as an estimate of the bacteriological cures for each pathogen type and for each treatment group. Somatic cell counts of cows were compared between treatment groups and within pathogen group. The number of cows that completed a full lactation were compared between each treatment group and within each pathogen group.


RESULTS
Treatment had no effect upon bacteriological cures, irrespective of pathogen present or the presence of bacteria during the previous lactation. There was no effect of treatment upon somatic cell count except for cows infected with Streptococcus dysgalactiae in which treatment caused a significant lowering of cell counts. This effect was not present in the subsequent lactation. Treatment of chronically infected cows did not alter the probability of a cow completing a full lactation but did improve the probability of newly infected cows being retained for the next lactation. Twenty-eight of 214 treated cows developed clinical mastitis in more than one quarter after treatment, thus indicating a poor technique by farmers for the insertion of intramammary antibiotics.


CONCLUSIONS
Treatment during lactation of cows with high somatic cell counts in milk is ineffective in reducing bacterial infections and in reducing somatic cell counts to acceptable numbers.
Shephard
R W
RW
Maffra Veterinary Centre, 10 Johnson Street, Maffra, Victoria 3860.
Malmo
J
J
Pfeiffer
D U
DU
D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000627:therapeutic use*; D002417:Cattle; D003023:Cloxacillin / Q000008:administration & dosage / Q000627:therapeutic use*; D003612:Dairying; D004334:Drug Administration Schedule; D004917:Erythromycin / Q000008:administration & dosage / Q000627:therapeutic use*; D005260:Female; D007267:Injections / Q000662:veterinary; D007774:Lactation; D008414:Mastitis, Bovine / Q000188:drug therapy*; D008892:Milk / Q000166:cytology* / Q000382:microbiology*; D010406:Penicillins / Q000008:administration & dosage / Q000627:therapeutic use*; D016896:Treatment Outcome
D000900:Anti-Bacterial Agents; D010406:Penicillins; D004917:Erythromycin; D003023:Cloxacillin