THE GENETIC FOUNDATION OF FITNESS AND REPRODUCTION TRAITS IN AUSTRALIAN PIG-POPULATIONS .1. GENETIC-PARAMETERS FOR WEANING TO CONCEPTION INTERVAL, FARROWING INTERVAL, AND STAYABILITY

Data from 2 large Australian piggeries were used to estimate genetic p arameters and to examine fixed effects for weaning to conception inter val (WCI) and farrowing interval (FI) measured in the first 3 reproduc tive cycles, and sow stayability from the first to later i parities (S TAY(1i)). WCI and FI recorded following the first farrowing had low he ritabilities (h(2) = 0.08-0.10), but estimates did not significantly d iffer from zero when these traits were recorded in later parities. Her itability estimates for STAY increased with parity of recording, rangi ng from 0.05 for STAY(12) to 0.06 (STAY(13)) and 0.09 (STAY(14)). Gene tic correlations between WCI12 or FI12 and stayability traits ranged f rom -0.22 to -0.54. Selecting for short WCI following the first farrow ing should have favourable consequences for longevity of sows. Importa nt fixed effects for WCI and FI were lactation length and the number o f piglets nursed. Both short (<20 days) and long (>29 days) lactation periods led to an increase in WCI12 relative to the optimum lactation length of 21-23 days. WCI also increased with the number of piglets nu rsed by 1 day/additional piglet for litters ranging in size from <7 to >10 piglets. STAY was little affected by correcting for the average n umber of piglets born in previous litters.