Genetic parameters for piglet mortality, within litter variation of birth weight, litter size and litter birth weight.

Genetic parameters were estimated for litter traits from 2297 litters of 1767 sows from three maternal lines of a commercial breeding herd. Heritability estimates were 0.05 and 0.06 for total number of piglets born (NBT) and number of piglets that died per litter (NDIED). Heritabilities were higher for total litter weight (TLWB: 0.16), average piglet weight per litter (APWB: 0.31) and the harmonic mean (HMPWB: 0.28). Selection to reduce within litter variation is achievable given the heritability of 0.11 for coefficient of within litter variation (CVPWB). Litter size (NBT) was positively correlated with TLWB (rg: 0.54) and NDIED (rg: 0.76), but had no significant genetic relationships with the other traits. Litter mortality was negatively correlated (rg: -0.46) with APWB and HMPWB. HMPWB is genetically the same trait as APWB and does not provide additional information. The alternative description of within-litter variation (CVPWB) had no significant genetic correlation with other litter traits and provides little opportunity for genetic improvement of litter mortality. Instead, APWB should be considered in selection programs in addition to litter size to improve piglet weights and piglet survival.