Estimation of genetic parameters for litter size in Canadian Yorkshire and Landrace swine with each parity of farrowing treated as a different trait.

Abstract

Genetic variances and covariances for the number of pigs born in total (NOBT), the number of pigs born alive (NOBA), and the number of weaned pigs (NOW) were estimated by REML under an animal model. Data on 30,357 and 42,041 litters born between 1977 and 1992 from Yorkshire and Landrace sows, respectively, were obtained from the Quebec Record of Performance sow productivity program. Data of the first four parities of litter size were used for four different analyses under an animal model: univariate analyses with direct genetic effects only, univariate analyses with maternal and direct genetic effects , seri0s of bivariate analyses with each parity treated as a different trait, and a series of bivariate analyses between NOBT, NOBA, and NOW within each parity. Heritabilities of different parities from univariate analyses under a direct genetic effects model ranged from .10 to .15, .09 to .14, and .06 to .08 for NOBT, NOBA, and NOW, respectively. Estimates of direct heritability from bivariate analyses between parties were consistent with estimates from univariate analyses in Landrace but not in Yorkshire. Genetic correlations between first and secondary parity in Yorkshire were .59, .49, and .17 for NOBT, NOBA, and NOW, and in Landrace were .90, .93, and .81, respectively. Influence of maternal effects on moderate correlations between first and secondary parity in Yorkshire was suggested. Genetic correlations averaged over all parities between NOBA and NOBT or NOW were .97 and .65 in Yorkshire and .97 and .82 in Landrace. A multiple-trait animal model with parities treated as different traits was recommended.

Genetic parameters for litter size in Black Slavonian pigs

“…Low genetic correlations between litter size in different parities indicates that phenotype records from different parities should be treated as different traits (Irgang et al, 1994;Roehe & Kennedy, 1995). Direct additive genetic correlations obtained with MT analysis for six traits are lower than in Hanenberg et al (2001), who reported an increase from 0.79 between the first and the second parity to 0.96 between the fifth and the sixth parity.…”

“…Knowledge of genetic parameters for litter size in pigs is necessary to estimate accurate breeding values, to optimize breeding schemes, and to predict response to selection (Roehe & Kennedy, 1995). There are several approaches regarding the method for genetic evaluation of litter size.…”

Estimation of variance components, genetic parameters and genetic trends for litter size of swines

“…These results are similar to those found in the present study. However, Roehe & Kennedy (1995) and Holm et al (2005) reported heritability estimates for number of piglets born of about 0.10 when using a model that only included first parity records of Landrace pigs.…”

“…These variations are due to the number and quality of the records and the models and estimation methods used. Additionally, there are some controversies in the literature as to whether litter size in different parities should be considered as repeated measurements of the same trait (Southwood & Kennedy, 1990;See et al, 1993;Crump et al, 1997;Lourenço et al, 2008) or as different traits (Irgang et al, 1994;Roehe & Kennedy, 1995;Rydhmer et al, 1995;Barbosa et al, 2008).…”

“…In the literature, the genetic correlation for litter size among parities generally exceeds 0.70 between the first and subsequent parities (Knap et al, 1993;Irgang et al, 1994;Roehe & Kennedy, 1995;Tholen et al, 1996;Alfonso et al, 1997;Hanenberg et al, 2001).…”