Table 5.
Negative binomial regression model in a study of herd-level risk factors for on-farm cow mortality in 4,252 Swedish dairy herds from September 2009 to August 2010.
| Variable | Category | MR1 ratio | 95% CI | P-value2 |
|---|---|---|---|---|
| Calving interval, d | <391.8 | 1 | <0.001 | |
| 391.8 to 407.3 | 1.10 | 1.03, 1.17 | ||
| 407.4 to 429.1 | 1.15 | 1.08, 1.22 | ||
| ≥429.2 | 1.29 | 1.20, 1.37 | ||
| Herd size × season3,4 | 20 to 49.9, autumn-winter | 1 | <0.001 | |
| 20 to 49.9, winter-spring | 1.39 | 1.28, 1.51 | ||
| 20 to 49.9, summer | 1.46 | 1.34, 1.59 | ||
| 50 to 99.9, autumn-winter | 1.33 | 1.22, 1.45 | ||
| 50 to 99.9, winter-spring | 1.42 | 1.30, 1.55 | ||
| 50 to 99.9, summer | 1.51 | 1.38, 1.64 | ||
| 100 to 199.9, autumn-winter | 1.52 | 1.38, 1.68 | ||
| 100 to 199.9, winter-spring | 1.58 | 1.45, 1.78 | ||
| 100 to 199.9, summer | 1.69 | 1.47, 1.93 | ||
| ≥200, autumn-winter | 1.85 | 1.53, 2.23 | ||
| ≥200, winter-spring | 1.69 | 1.47, 1.93 | ||
| ≥200, summer | 1.66 | 1.46, 1.89 | ||
| Housing system5 × milk yield, kg of ECM | Tie-stall, <8,421 | 1 | <0.001 | |
| Tie-stall, 8,421 to 9,279 | 0.98 | 0.89, 1.08 | ||
| Tie-stall, 9,280 to 9,994 | 0.92 | 0.84, 1.01 | ||
| Tie-stall, ≥9,995 | 0.93 | 0.85, 1.01 | ||
| Freestall AMS, <8,421 | 1.03 | 0.91, 1.16 | ||
| Freestall AMS, 8,421 to 9,279 | 1.12 | 1.00, 1.27 | ||
| Freestall AMS, 9,280 to 9,994 | 0.92 | 0.82, 1.03 | ||
| Freestall AMS, ≥9,995 | 0.81 | 0.70, 0.92 | ||
| Freestall CM, <8,421 | 1.15 | 1.02, 1.30 | ||
| Freestall CM, 8,421 to 9,279 | 1.06 | 0.93, 1.19 | ||
| Freestall CM, 9,280 to 9,994 | 0.97 | 0.87, 1.08 | ||
| Freestall CM, ≥9,995 | 0.92 | 0.82, 1.03 | ||
| Management type | Conventional | 1 | <0.001 | |
| Organic | 0.80 | 0.74, 0.88 | ||
| Predominant breed | Swedish Holstein | 1 | <0.001 | |
| Swedish Red | 0.76 | 0.71, 0.82 | ||
| Mixed/other breeds6 | 0.87 | 0.83, 0.92 | ||
| Region7 | Södra Götaland (1) | 1 | <0.001 | |
| Östra Götaland (2) | 1.07 | 0.99, 1.17 | ||
| Västra Götaland (3) | 0.97 | 0.90, 1.06 | ||
| Östra Svealand (4) | 0.96 | 0.86, 1.08 | ||
| Västra Svealand (5) | 1.06 | 0.93, 1.20 | ||
| Norrland (6) | 1.10 | 1.01, 1.21 |
1
Mortality rate.
2
Significance level (Wald test) of main effects or combined effects.
3
Autumn-winter (September 1 to December 31), winter-spring (January to April 30), and summer (May 1 to August 31).
4
The combined effect of the main variables.
5
Tie-stall = tie-stall with pipeline milking; freestall AMS = freestall with automatic milking system; freestall CM = freestall with conventional milking (e.g., milking parlor or carousel).
6
Crossbreeds, Swedish Polled and Swedish Jersey.
7
Numbers in parentheses refer to different regions identified in Figure 1.