Table 6.
Over-dispersed Poisson regression Models 2–4 of risk factors associated with the incidence rate of clinical mastitis. Model 2—ewes housed in barns before lambing, Model 3—ewes housed at lambing, Model 4—ewes housed after lambing.
| Variable | IRCM | RR | Lower CI | Upper CI | |
|---|---|---|---|---|---|
| Model 2 before lambing (n = 230) | |||||
| Intercept-4.82 (0.18) | |||||
| Percentage of flock with poor udder conformation | 1.12 | 1.06 | 1.17 | ||
| Base material of the floor | Hardcore | 1.03 | Reference | ||
| Concrete | 1.69 | 1.56 | 1.09 | 2.22 | |
| Earth | 1.41 | 1.55 | 1.07 | 2.24 | |
| Other | 1.20 | 1.82 | 1.15 | 2.90 | |
| Model 3 during lambing (n = 247) | |||||
| Intercept-5.11 (0.41) | |||||
| Percentage of flock with poor udder conformation | 1.08 | 1.01 | 1.15 | ||
| Base material of the floor | Hardcore | 1.05 | Reference | ||
| Concrete | 1.52 | 1.87 | 1.11 | 3.13 | |
| Earth | 1.30 | 1.62 | 0.88 | 2.97 | |
| Other | 1.15 | 1.53 | 0.79 | 2.95 | |
| Bedding storage | Outdoors uncovered | 1.23 | Reference | ||
| Outdoors covered | 1.62 | 2.54 | 1.09 | 5.96 | |
| In a building | 1.34 | 1.34 | 0.72 | 2.48 | |
| Mixed | 1.73 | 1.03 | 0.21 | 4.97 | |
| Model 4 after lambing (n = 187) | |||||
| Intercept-5.07 (0.33) | |||||
| Percentage of flock with poor udder conformation | 1.13 | 1.06 | 1.19 | ||
| Base material of the floor | Hardcore | 0.88 | Reference | ||
| Concrete | 1.48 | 1.88 | 0.95 | 3.69 | |
| Earth | 1.47 | 2.59 | 1.25 | 5.38 | |
| Other | 1.45 | 2.00 | 0.95 | 4.19 | |
| Frequency of adding fresh bedding | Weekly | 3.00 | Reference | ||
| Twice a week | 1.34 | 0.52 | 0.39 | 0.93 | |
| Every two days or less | 1.40 | 0.52 | 0.23 | 1.16 | |
RR = Risk ratio. Lower and upper CI = 95 percent confidence intervals for the risk ratio. IRCM = incidence rate of clinical mastitis: no. ewes/100 ewes/year with clinical mastitis.