Evaluation of litters per sow per year as a means to reduce non-productive sow days in commercial swine breeding herds and its association with other economically important traits

The purpose of this project was to determine the value of implementing litters per sow per year (LSY) into a selection program. Two studies were conducted to achieve this objective. The goal of one study was to determining the genetic and phenotypic relationships between LSY and other economically important reproductive and post-weaning traits from a commercial swine breeding company. Determining the genetic and phenotypic correlations among traits can help breeders evaluate the expected impacts their selection decisions have on other economically important production traits. These other economically important traits may or may not be included in the selection criteria. This is particularly important when considering reproductive and post-weaning traits because of the undesirable genetic relationships that typically exist between reproductive and post-weaning traits. The traits collected included number born alive (NBA), wean to estrus (W2E), adjusted back fat (BF), percent lean (PCL), and days to 100 kg (D100). Litters per sow per year (LSY) was calculated based on recorded information. Genetic parameter estimates were calculated using ASREML. The heritability estimates for NBA, LSY, W2E, BF, D100, and PCL were 0.15, 0.03, 0.03, 0.52, 0.33, and 0.36, respectively. The genetic correlation between LSY and W2E was large and favorable. The genetic correlations between LSY and the three post-weaning traits (BF, D100, and PCL) have large standard errors and are unclear in direction. Some economically important traits can be favorably changed indirectly with selection on LSY; however, a selection index will be needed to ensure that post-weaning growth traits are not adversely affected by selection for LSY in a maternal line breeding program. The goal of the second study was to determine the relationship between individual sire breeding values (BV) for LSY and progeny means for farrowing rate, removal parity, and lifetime born alive. Landrace, Large White, and F1 (YyL or LyY) crossbred females were included in the analyses. Estimated breeding values (EBV) for LSY were calculated using ASREML. The heritability estimate for LSY was 0.11. Sire progeny (daughter) farrowing rate means were calculated as total number of services of the sire\u27s daughters divided by the total litters farrowed from the sire\u27s daughters. Similar values were calculated for daughter average removal parity, and daughter average lifetime born alive. The Spearman rank correlation between the LSY EBV and the progeny farrowing rate of the sires was calculated using SAS software. When all sires with 10 or more daughters were included in the analysis, the Spearman rank correlations between the sire\u27s LSY EBV and daughter means for farrowing rate, removal parity, and lifetime born alive were 0.49, 0.23, and 0.25 (P\u3c0.01). The LSY EBV was favorably correlated with the daughter means for all three traits. This provides evidence that selecting sires with high LSY EBV to improve the LSY could also improve the herd farrowing rate, removal parity, and lifetime born alive. Sires ranked in the top 25% for LSY EBV had a 15.3% higher average farrowing rate compared to sires in the bottom 25%. Daughters from the top sire had a one parity greater average removal parity than daughters from the other sire group. This extra litter corresponded to an average of 8.9 more pigs produced in a sow\u27s lifetime. Based on the results of this project, LSY is heritable. There is a genetic component of LSY and there is sufficient biological variation of the trait for traditional selection methods to be efficient and effective. There are little to no antagonistic relationships between LSY and the other economically important traits considered in this study. A selection index must be employed to ensure that there is no adverse effect on other economically important traits when selecting for LSY. There is evidence to suggest that a desirable relationship exists between LSY and farrowing rate, removal parity, and lifetime born alive. Improving farrowing rate through improving LSY can reduce the number of costly non-productive sow days in the herd. Improving removal parity and lifetime born alive through increasing LSY could improve sow longevity