30
Variance component estimates for alternative litter size and piglet mortality traits
The objective of this study was to estimate variance components for litter size and mortality traits at different time points. Traits analyzed included; number born alive (NBA), litter size at day 2 (LS2), litter size at day 5 (LS5), litter size at day 30 (LS30), piglet mortality at day 5 (MortD5) and piglet mortality at day 30 (MortD30). Day 30 was chosen for two reasons. (1) The average wean age over the four years was 23.5 days and (2) it is important to include mortalities from early docking in the nursery phase. Data were obtained on 8653 Large White litters from Smithfield Premium Genetics collected from June 2009 through May 2013. Data management and phenotypic analyses were completed with the R statistical environment. Litter size traits were the number of pigs alive on the respective number of days post-farrowing. All mortality traits were calculated as percentage of dead pigs from TNB on each of the respective days post-farrowing, including stillborn piglets. Genetic analyses were completed using the BLUPF90 family of programs. A basic animal model was fit with fixed effects of parity, year-season, farm, and random effect of permanent environment. Two-trait models were fit between all combinations of traits. Heritability estimates of traits were averaged over the models in which they were involved. All traits were treated as traits of the birth sow, ignoring cross-fostering effects. Heritability estimates for NBA, LS2, LS5, LS30, MortD5, and MortD30 were 0.094, 0.082, 0.097, 0.088, 0.089, and 0.104, respectively. Phenotypic variance estimates for NBA, LS2, LS5, LS30, MortD5 and MortD30 were 12.11, 10.93, 9.74, 8.87, 0.033 and 0.024, respectively. Phenotypic and genetic correlations between LS2 with NBA, LS5, LS30, MortD5 and MortD30 were 0.92, 0.95, 0.83, -0.23 and -0.09 and 0.95, 0.98, 0.89, -0.47 and -0.34, respectively. Phenotypic and genetic correlations between LS5 with NBA, LS30, MortD5, and MortD30 were 0.86, 0.90, -0.38 and -0.23 and 0.87, 0.96, -0.55 and -0.46, respectively. LS2 or LS5 could be used as alternatives to NBA as the main component trait of maternal line breeds to increase NBA and decrease pre-weaning mortalities.
Keywords:
genetic correlation, litter size, piglet mortality