Estimates of genetic parameters for reproduction traits at different parities in Dutch Landrace pigs

Data from Dutch Landrace sows were used to estimate genetic parameters for reproduction traits in the first six parities. Analyses were performed with DFREML using a model with equal design and herd-year-season of first parit y as a fixed effect. Estimates of genetic parameters were calculated for di fferent traits and parities using data from 58 194 sows. Heritabilities wer e found to be low for farrowing after first insemination (FFI), mothering a bility (MA) and number of still born piglets (NSB); moderate for number of piglets born in total (NBT) or alive (NBA) and interval from weaning to fir st insemination (IWI); and high for gestation length (GL) and age at first insemination (AFI). Heritability increased slightly with parity number for NET and NEA. increased markedly for NSB and MA, and decreased for IWI. Gene tic correlations between the same traits measured in different parities wer e close to unity for parities higher than 2, for all traits. Genetic correl ations below 0.70 were found between parity 1 and higher parities, for NET, NEA, NSB, MA and FFI. Undesirable correlations were found between NET and NSB (0.53) and NET and MA (-0.49). Indirect selection on MA would be possib le using GL (r(g) = 0.40). IWI was positively correlated with AFI (0.31). I t is concluded that selection on litter size. piglet mortality and also num ber of litters per year would be worthwhile. (C) 2001 Elsevier Science B.V. All rights reserved.