| dc.description.abstract | This study, an investigation of coagulase positive (CPS) and coagulase negative (CNS)
staphylococcal mastitis in 44 randomly selected dairy herds in Prince Edward Island (PEl) had three
major objectives. These are:
1. to survey dairy management factors and determine the effect of management factors on the herd
prevalence of staphylococcal mastitis pathogens.
2. to survey antimicrobial sensitivity of Staphvlococcus isolates from the study herds, and assess which
management factors affect sensitivity of staphylococcal mastitis pathogens to these antimicrobials.
3. to determine if significant correlations exist between the prevalence of staphylococcal mastitis
pathogens and their in vitro antimicrobial sensitivity.
Information on dairy management practices and antibiotic use was sought through a mail out
questionnaire. A response rate of 77% was realized. Adoption rates of 79% and 48% for postmilking
teat dipping and dry cow therapy for all cows in a herd were observed. Cloxacillin benthazine
and Oxytetracyline hydrochloride were the most widely used dry cow products, on 48% and 32% of
farms respectively. Seventy eight percent of the farms used products containing beta lactams, 48%
of these contained Penicillin G.
Weighted least squares multiple regression was used to relate the within herd prevalence of
CPS or CNS to management factors and, separately, to dry cow products. For CPS, farms that dipped
teats after milking were significantly associated with low prevalence. The number of times the milking
machine was checked had a weak positive correlation with prevalence. Dry cow products used had
no association with the prevalence of CPS. Freestall and ties tall versus loose housing, high-line
milking system versus bucket milking, and pre-partum teat dipping were associated with low
prevalence of CNS. Farms that used a dry cow product containing procaine penicillin G and
novobiocin sodium were associated with low prevalence of CNS, while farms that used any dry cow
product containing novobiocin were associated with high prevalence.
All CPS isolates and a sub-sample representing 25% of CNS isolates were tested for
sensitivity to 13 antimicrobials using the disc diffusion method. Among CPS, sensitivity was above
91% to all the antimicrobials tested except penicillin G, ampicillin, neomycin, and polymyxin B.
Among the CNS, sensitivity was above 91% except penicillin G, ampicillin, polymyxin B, tetracycline,
and sulphamethoxazole / trimethoprim. There was between farm variation in sensitivity for both CPS
and CNS. When farm factors were taken into account, the proportions of CPS sensitive to
tetracycline, sulphamethoxazole / trimethoprim, and nitrofurantoin were significantly higher than
CNS. The proportions of CNS sensitive to neomycin and polymyxin B were significantly higher than
CPS. Sensitivity to penicillin G, ampicillin, and erythromycin was strongly affected by farm level
factors.
Weighted least squares multiple regression was used to relate the proportions of CPS and
CNS sensitive to penicillin G or tetracycline to management factors and, separately, to dry cow
products. Among CPS, post-milking teat dipping was associated with high sensitivity to penicillin G
and tetracycline. The milking herd proportion culled because of mastitis had a negative correlation
with sensitivity for tetracycline. Neither the herd proportion receiving dry cow therapy nor the dry
cow products used had any association with CPS sensitivity to Penicillin G or tetracycline. Among
the CNS, post-milking teat dipping, dipping milking cluster between cows and the herd proportion
receiving dry cow therapy had positive correlations with sensitivity to penicillin G. The milking herd
proportion treated for clinical mastitis and the herd proportion receiving dry cow therapy had negative
correlations with CNS sensitivity for tetracycline, while the herd proportion culled because of mastitis
had a positive correlation. Dry cow products used predicted CNS sensitivity to penicillin G and
tetracycline.
The association between the proportions of CPS or CNS sensitive to penicillin G and
tetracycline in vitro and the herd prevalence were sought after taking into account farm factors using
the partial correlation coefficient. No significant associations were found. | en |
