Fig. 3

Number of bacterial colony-forming units (CFUs) per gram of feces. Total number (log₁₀ CFUs/g) of A) Gram-negative and B) Gram-positive bacteria recovered from each sample in the ceftiofur-treated (orange) and control (gray) cows. Numbers of ceftiofur-resistant C) Gram-negative and D) Gram-positive bacteria are also shown along with the number of ampicillin-resistant E) Gram-negative and F) Gram-positive bacteria. Numbers are plotted before (Day − 1) and after treatment for Gram negative bacteria through 9 weeks and after 1 week for Gram-positive bacteria. Line plots show means and standard error bars with sample counts represented as dots. Boxplots indicate the median, lower, and upper quartiles, and the whiskers represent extreme values in the distribution. P-values were calculated using a paired Wilcoxon signed rank test to compare treatment groups within a sampling point and the same group across two samplings. The per animal variability over time was calculated with the Friedman rank-sum test (FT), which accounts for repeated measures and is shown per treatment group for the Gram-negative bacteria. Significant p-values between sampling points are represented for all cows (black) as well as control (grey) and antibiotic-treated (orange) cows