Objective—To evaluate various sampling strategies for potential use in measuring prevalence of antimicrobial susceptibility in cattle.
Sample Population—500 isolates of non–type-specific Escherichia coli (NTSEC) isolated from the feces of 50 cows from 2 dairy farms (25 cows/farm and 10 isolates/cow).
Procedures—Diameters of inhibition zones for 12 antimicrobials were analyzed to estimate variation among isolates, cows, and farms and then used to determine sampling distributions for a stochastic simulation model to evaluate 4 sampling strategies. These theoretic sampling strategies used a total of 100 isolates in 4 allocations (1 isolate from 100 cows, 2 isolates from 50 cows, 3 isolates from 33 cows, or 4 isolates from 25 cows).
Results—Analysis of variance composition revealed that 74.2% of variation was attributable to isolates, 18.5% to cows, and 7.3% to farms. Analysis of results of simulations suggested that when most of the variance was attributable to differences among isolates within a cow, culturing 1 isolate from each of 100 cows underestimated overall prevalence, compared with results for culturing more isolates per cow from fewer cows. When variance was not primarily attributable to differences among isolates, all 4 sampling strategies yielded similar results.
Conclusions and Clinical Relevance—It is not always possible to predict the hierarchical level at which clustering will have its greatest impact on observed susceptibility distributions. Results suggested that sampling strategies that use testing of 3 or 4 isolates/cow from a representative sample of all animals better characterize herd prevalence of antimicrobial resistance when impacted by clustering.
Objective—To determine the percentage of broodmares
and foals that shed Clostridium perfringens in
their feces and classify the genotypes of those isolates.
Design—Prospective cross-sectional study.
Animals—128 broodmares and their foals on 6
Procedures—Anaerobic and aerobic bacteriologic
cultures were performed on feces collected 3 times
from broodmares and foals. All isolates of C perfringens
Results—Clostridium perfringens was isolated from
the feces of 90% of 3-day-old foals and 64% of foals
at 8 to 12 hours of age. A lower percentage of broodmares
and 1- to 2-month-old foals shed C perfringens
in their feces, compared with neonatal foals. Among
samples with positive results, C perfringens type A
was the most common genotype identified (85%); C
perfringens type A with the β2 toxin gene was identified
in 12% of samples, C perfringens type A with the
enterotoxin gene was identified in 2.1% of samples,
and C perfringens type C was identified in < 1% of
Conclusions and Clinical Relevance—Clostridium
perfringens was identified from the feces of all but 6
foals by 3 days of age and is likely part of the normal
microflora of neonatal foals. Most isolates from
broodmares and foals are C perfringens type A; thus,
the clinical relevance of culture results alone is questionable.
Clostridium perfringens type C, which has
been associated with neonatal enterocolitis, is rarely
found in the feces of horses. (J Am Vet Med Assoc