Table 1.
Characteristics of farms with different antibiotics use: i) normal use (NORM), being no more than 2 times/cow/yr of antibiotic use, and ii) excessive use (HIGH), being more than 2 times/cow/yr
| NORM | HIGH | Statistic value | p-value | |
|---|---|---|---|---|
| Farm characteristics | ||||
| Number of farms | 8 | 10 | ||
| Total cows in farms | 110 | 128 | ||
| Average cows per farm | 13.75 | 12.80 | ||
| Subclinical mastitis prevalence in the last 3 months prior to study | 0.43 | 0.35 | 4.53 | 0.04 |
| Cow characteristics (mean±SEM) | ||||
| Average parity | 2.66±0.23 | 3.71±0.34 | −2.55 | 0.01 |
| Average days in milk (days) | 239±21.1 | 173±15.4 | 2.31 | 0.02 |
| Geometric mean of somatic cells | 845 | 580 | 1.65 | 0.10 |
| Geometric mean of somatic cells in the last 3 months prior to study | 387 | 361 | 0.21 | 0.83 |
| Sample characteristics | ||||
| Number of subclinical mastitis cows | 38 | 38 | 0.44 | 0.51 |
| Number of sampling cows | 36 | 37 | ||
| Number of quarter samples | 140 | 147 | ||
| Positive intramammary-infected cows | 23 | 24 | 0.00 | 1.00 |
| Positive intramammary-infected quarters | 50 | 56 | 0.09 | 0.77 |
| Number of swab samples (cows) | 12 | 15 | ||