Heritability estimates from the Model 2 that balances fit with computational ease and data structure were .29 for days and .35 for backfat. Genetic parameters for days to 114 kg in Duroc swine. Genetic parameters for adjusted backfat depth in Duroc swine. This increase in heritability estimate would be expected to create a wider distribution among EPDs, resulting in more desirable numbers for trait leaders. However, to accurately estimate litter effects sows should have more than 1 litter.
Consideration needs to be given to data structure and multiple litters per nucleus female.
Model 3 was fit only to describe the observed increase in heritability from adding maternal genetic effects and the result do not significantly differ from model 2. The results indicate that the large negative genetic correlation between direct and maternal effects causes the increase in both direct and maternal heritabilites. To accurately estimate maternal genetic effects and correlation between direct and maternal effects sires should have multiple daughters with measured progeny and daughters should have multiple litters with measured offspring. This also raises concerns over contemporary group structure and numbers of records per female and sire. It should also be considered that Model 2 is more conservative by not taking into account maternal and permanent environmental effects that are prone to errors due to data structure.