Table 4.

Associations between first parity litter size and sows’ odds of producing ≥4 litters in her lifetime

Explanatory variable	OR	P value	95 % Conf. interval
Categories
Number of piglets
≤8	0.81	0.000	0.74	0.88
9	0.92	0.118	0.83	1.02
10	0.99	0.834	0.91	1.08
11	1.01	0.760	0.93	1.10
12	1.05	0.266	0.97	1.13
13	Ref.
14	0.97	0.509	0.90	1.05
15	0.89	0.008	0.82	0.97
16	0.96	0.443	0.87	1.06
≥17	0.85	0.001	0.77	0.94
Birth year of the sow
≤2002	Ref.
2003–2006	0.71	0.000	0.67	0.76
2007–2008	0.67	0.000	0.62	0.71
2009	0.68	0.000	0.63	0.73
Age (days) at first farrowing
≤347	Ref.
348–363	1.00	0.920	0.94	1.07
364–384	0.92	0.012	0.87	0.98
≥385	0.85	0.000	0.79	0.90
Season at first farrowing
Winter	Ref.
Spring	0.92	0.006	0.87	0.98
Summer	0.88	0.000	0.83	0.93
Fall	0.98	0.512	0.92	1.04

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 38,346 observations