BREED-SPECIFIC ADJUSTMENT FACTORS FOR REPRODUCTIVE TRAITS IN DUROC, HAMPSHIRE, LANDRACE, AND YORKSHIRE SWINE

Number born alive (NEA) and litter weaning weight (LWT) can be influen ced by many factors, including environment, parity, age at farrowing, lactation length, and genetic merit as well as number of pigs after tr ansfer (NAT) and weaning age (WNAGE) for LWT. The objectives of this s tudy were to estimate adjustment factors for NEA and LWT using all eff ects 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 fixe d effects of contemporary groups and parity/age class, random direct g enetic 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 bre eding within P1 and P2 was found and new adjustments were found to dif fer from previous studies. In the Yorkshire population, for example, t he average P1 adjustment was 1.0 pig in this study, compared to the cu rrent .69; however, this ranges from 1.46 for the youngest P1 females to .57 for the oldest. Similarly, in P2 the average adjustment was fou nd 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 l itter records for LWT. A residual analysis showed nonsignificant diffe rences (P > .60) across the age classes after using the new adjustment s; however, significant differences (P < .01) remained after using the current adjustments.