The objective of the present study was to estimate heritabilities and genetic correlations for semen and litter size traits using full animal model analyses. Litter size data were available from 28,485 Czech Large White and 10,410 Czech Landrace sows farrowing between 1995 and 2008. The number of litter records was 91,922 and 30,937, respectively. Records on semen traits (37,137 ejaculates from 778 Large White boars and 51,341 ejaculates from 841 Landrace boars) were available from 22 AI centers in the Czech Republic from 2000 to 2009. All calculations were carried out separately for each breed. Number of functional sperm was defined as total number of sperm times the fraction of motile sperm times (1 – the fraction of abnormal sperm). Among the semen traits, semen volume showed the greatest heritability (0.20 in Large White and 0.25 in Landrace), followed by sperm concentration with a heritability of 0.18 in both breeds. The heritabilities of the remaining 4 traits (motility, percentage of abnormal sperm, total number of sperm, and number of functional sperm) were around 0.10. Large negative genetic correlations were observed between semen volume and sperm concentration and between motility and percentage of abnormal sperm, especially in Large White. Positive and negative correlations among remaining semen traits were mostly of small magnitude. There was a tendency for increasing litter size to be associated with slight decreases in the total number of sperm and in the number of functional sperm, especially in the Large White breed (genetic correlations of −0.08 to −0.14 and −0.16 to −0.31, respectively, with SE between 0.100 and 0.114). Some of the correlations between semen and litter size traits (especially with the percentage of abnormal sperm) were breed-specific (positive up to 0.63 for Large White and negative until −0.41 in Landrace). Furthermore, parity-specific correlations were observed in the Large White breed.

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