Genetic parameters and selection strategies for female fertility and litter quality traits in organic weaner production systems with closed breeding systems

The increase of litter sizes in conventional weaner production systems in the past 30 years is associated with decreasing piglet birth weights, and in further consequence, with increasing piglet mortality. The aim of this study was the implementation of practicable litter quality recording schemes in six participating organic herds, in order to record new litter quality traits for the estimation of genetic parameters and breeding values. The litter quality traits were “Average Piglet Birth Weight” (ABW), “Litter Evenness” (LE), and “Piglet Vitality” (PV). Litter quality traits were recorded on a scale from 1 to 4, whereas score 4 indicated the desired performance value. A further female fertility trait was the “number of live born piglets” (LBP). The dataset included 2602 recorded litters from 1102 German Landrace x German Large White crossbred sows (rotational crossing system) from the birth years 2007 to 2015. For the estimation of genetic (co)variance components, univariate and bivariate animal models were applied. Heritability estimates for the litter quality traits were 0.09 for LE, 0.14 for PV and 0.21 for ABW. Genetic correlations among litter quality traits were throughout large and favourable, i.e., 0.90 between LE and ABW, 0.90 between LE and PV, and 0.75 between ABW and PV. Genetically, all new litter quality traits were negatively correlated with LBP (genetic antagonistic relationship). Estimated genetic (co)variance components were input parameters in selection index calculations. The aim was the identification of an optimal selection strategy for organic weaner production systems, i.e., an optimised breeding goal for the selection of replacement sows from the own herd. Using a desired gain approach, we focussed on the maximisation in genetic gain for litter quality traits, while keeping the status quo for LBP. The optimal index scenario included the phenotypic information from all four traits from the selection candidate (sow) from two litters. At the same time, three litters from the dam of the sow, and one litter from 10 half sibs, were available as information sources. For such a design of information sources and genetic relationships, optimal economic weights were 7.50 € for LBP and 20 € for all litter quality traits LE, ABW and PV. The correlation between the index and the aggregated genotype from this scenario was 0.60. Genetic gain per year considering a generation interval of 2.80 years for organic weaner production systems was larger than 0.04 points for all litter quality traits.