Table 6.
Associations between first and second parity litter size and sows’ odds of producing ≥4 litters in her lifetime
| Explanatory variable | OR | P value | 95 % Conf. interval | |
|---|---|---|---|---|
| Categories | ||||
| Exposure groupa | ||||
| S1S2 | 0.75 | 0.000 | 0.68 | 0.82 |
| S1M2 | 0.98 | 0.683 | 0.89 | 1.08 |
| S1L2 | 0.89 | 0.025 | 0.80 | 0.99 |
| M1S2 | 0.86 | 0.002 | 0.78 | 0.94 |
| M1M2 | Ref. | |||
| M1L2 | 0.89 | 0.012 | 0.81 | 0.98 |
| L1S2 | 0.71 | 0.000 | 0.62 | 0.81 |
| L1M2 | 0.82 | 0.000 | 0.73 | 0.91 |
| L1L2 | 0.84 | 0.001 | 0.77 | 0.93 |
| Birth year of the sow | ||||
| ≤2002 | Ref. | |||
| 2003–2006 | 0.78 | 0.000 | 0.73 | 0.83 |
| 2007–2008 | 0.69 | 0.000 | 0.64 | 0.75 |
| 2009 | 0.68 | 0.000 | 0.62 | 0.74 |
| Age (days) at first farrowing | ||||
| ≤347 | Ref. | |||
| 348–363 | 1.00 | 1.000 | 0.93 | 1.07 |
| 364–384 | 0.95 | 0.141 | 0.88 | 1.02 |
| ≥385 | 0.87 | 0.000 | 0.81 | 0.94 |
Estimates of odds ratio (OR) from multivariable logistic regression of a sow producing ≥4 litters in her lifetime. In addition to the explanatory variables listed in the table, herd was included as a random variable in the model. Data were selected from January 1 1997 to December 31 2009 from 24 Swedish piglet producing herds and included 32,300 observations
aS = small litter size (≤11 piglets), M = medium litter size (12–14 piglets), L = large litter size (≥ 15 piglets), 1 = first parity and 2 = second parity