Breed-specific adjustment factors for reproductive traits in Duroc, Hampshire, Landrace, and Yorkshire swine.

Number born alive (NBA) and litter weaning weight (LWT) can be influenced by many factors, including environment, parity, age at farrowing, lactation length, and genetic merit as well as number of pigs after transfer (NAT) and weaning age (WNAGE) for LWT. The objectives of this study were to estimate adjustment factors for NBA and LWT using all effects in the model and to refine parity effects by including age of the sow in parity 1 (P1) and parity 2 (P2). The models used included fixed effects of contemporary groups and parity/age class, random direct genetic and permanent environment effects, as well as the fixed effects of NAT and WNAGE for LWT. A large effect due to age of the sow at breeding within P1 and P2 was found and new adjustments were found to differ from previous studies. In the Yorkshire population, for example, the average P1 adjustment was 1.0 pig in this study, compared to the current .69; however, this ranges from 1.46 for the youngest P1 females to .57 for the oldest. Similarly, in P2 the average adjustment was found to be .50, with an adjustment of .99 for the youngest P2 and 0 for the oldest. Also, age of dam was found to contribute variation to P1 litter records for LWT. A residual analysis showed nonsignificant differences (P > .60) across the age classes after using the new adjustments; however, significant differences (P < .01) remained after using the current adjustments.