Genetics of the interval from weaning to estrus in first-litter sows: correlated responses

The objective of this study was to evaluate relationships between rebreeding performance and growth performance (n = 3,777 gilts) and rebreeding performance and reproductive performance (n = 2,242 sows). Our data were from a selection experiment for shorter intervals from weaning to estrus after the first parity (IWE), involving Dutch Landrace pigs, in which a selection line and a control line without selection were maintained for eight generations. Relationships were evaluated before and after transforming IWE to normal interval (NI; IWE < or = 7 d), prolonged interval (PI; IWE > 7 d), and incidence of a prolonged interval (INC). Heritabilities of NI, PI, and INC were .18, .17, and .27. Within-line phenotypic and genetic trends in growth and reproductive performance were not different from zero and did not diverge as a correlated response to the selection applied. Phenotypic correlations between IWE, NI, or PI and growth or reproductive performance were low and ranged from -.14 to .11. Genetic correlations were higher, and, for the majority of traits, the genetic correlations with NI and PI had a different sign. Phenotypic and genetic contrasts between sows with NI and sows with PI different from zero indicated that INC may increase as a correlated response to selection for reproductive performance. Analyses using untransformed IWE or data from populations selected for rebreeding performance may underestimate the correlated response in IWE due to selection on economically important traits.