Estimation of genetic parameters for semen quality traits and growth rate in a paternal rabbit line

Variance components of sperm quality traits were estimated in a paternal line of rabbits selected on the basis of daily weight gain (DG, g/day) between 28 and 63 days of age. Features of the marginal posterior distributions for the genetic variance ratios, variance due to non-additive plus environmental permanent male effects, and variance due to litter of birth effects with respect to phenotypic variance are reported. The correlation between sperm quality traits and the selection criteria were also estimated. Nine sets of two-trait analyses were performed involving 12 908 DG records, 2231 ejaculates corresponding to 412 males, and 14 700 animals in the pedigree file. Heritability values (h(2)) of sperm quality traits commonly evaluated in a classic spermiogram were 0.18, 0.19, and 0.12 for normal acrosome status (NAR) (%, percentage of sperm with intact acrosome), sperm abnormalities (ANR) (%, percentage of sperm abnormalities), and sperm motility (MOT) (%, percentage of total motile sperm cells), respectively. The h(2) of some motion computer-assisted sperm analysis (CASA) Parameters 0.09, 0.11, 0.10, 0.11, 0.11 and 0.11 for average path velocity (VAP) (μm/sec; average path velocity), straight-line velocity (VSL) (μm/sec; straight-line velocity), curvilinear velocity (VCL) (μm/sec; curvilinear velocity), linearity index (LIN) (%, linearity index), amplitude of lateral head displacement (ALH) (μm; amplitude of the lateral head displacement) and straightness (STR) (%, straightness) were also estimated. Permanent environmental effects were lower than the corresponding values of h(2) and varied between 0.04 and 0.14. Genetic correlations between DG and sperm traits showed a high interval of highest density of 95% (HPD)(95%) (interval of highest density of 95%). However, there is some consistent evidence of the negativity of the genetic correlations of DG with NAR and MOT (-0.40 and -0.53, respectively). Permanent correlations were low, including the zero in the HPD(95%). Litter birth correlations between DG with LIN and STR showed that a favorable effect for growth could be detrimental for them (-0.47 and -0.53). Therefore, as the magnitude of the genetic correlations does not seem very high, it may be possible to define a selection index, including some sperm quality traits that allow improvement of DG without diminishing the semen quality.