The effect of scope of analyzed data on the value of the heritability coefficient of litter size traits in pigs

Low heritability of pig litter size traits at birth (number of live born piglets - LBP and total born piglets - TBP) and weaning (number of reared piglets - RP) is one of the major problems in their genetic improvement. The effect of selection is directly proportional to trait heritability and inversely proportional to the duration of generation interval. Objective of this study was to establish presence of difference in regard to heritability coefficient values of observed traits, as well as their accuracy depending on the size of data used in the analysis. Heritability coefficients in this study were calculated based on fertility results obtained for Swedish Landrace sows on three pig farms (farms 1, 2 and 3) in the Republic of Serbia. Observed traits - LBP, TBP and RP on farms 1, 2 and 3 were analyzed in the first (2422, 1677 and 2015 litters), in the first two (4190, 2897 and 3377 litters), in the first three (5576, 3809 and 4425 litters) and all available parities (9538, 6340 and 7750 litters) by applying the adequate mixed model of the Least square method. Heritability of LBP calculated based on fertility realized in the first partus ranged from 5.6 to 16.4 %, TBP ranged from 7.0 to 16.8 % and RP ranged from 3.4 to 7.7 %. Introduction into the analysis of the results pertaining to the second, third and subsequent parities lead mainly to detection of lower values of heritability coefficients for observed traits.