Variability, repeatability and phenotypic relationships of several characteristics of production and semen quality in...

A total of 2140 ejaculates from 156 adult males pertaining to four groups of bucks were analysed and the following traits were recorded: pH, ejaculate volume (V), mass motility (Mm), individual motility (Mi), concentration (Cn), total number of spermatozoa per ejaculate (TSE), percentage of sperm viability (Vi), percentage of sperm with acrosome integrity (NAR), percentage of sperm normalcy (Nr), percentage of sperm morphological abnormalities of head (H), neck-midpiece (Nm) and tail (T) and presence of proximal and distal cytoplasmic droplet (Dp, Dd). Principal component (PC) analysis and phenotypic correlations were performed in order to examine the relationships between qualitative and quantitative traits of rabbit semen. The repeatability of the traits measured was also estimated. Phenotypic correlations between sperm traits were estimated as the residual correlation from an analysis of variance, including the effects of: genetic type of the male, order of the ejaculate, day of collection and the permanent non-additive random effect of the male to which the observation corresponds. The repeatability of these traits was analysed separately, in a set of univariate analyses, using VCE software. The previously defined mixed model was used for this analysis. The principal component analysis was performed using the Princomp procedure of the SAS v.8 package. The first four PC explained 62% of total variation: 23%, 18%, 12% and 8%, respectively. Percentage of sperm viability, NAR, Nr, T and Nm were the predominant variables in the first PC. Mass motility, Mi, pH, Cn and TSE were located in the second. Percentage of sperm with the presence of proximal and distal cytoplasmic droplet, NAR, Vi and Nr were the predominant traits in the third and V defined the fourth. Repeatability of semen quality traits was moderate for most of the traits. The highest values (about 0.45) corresponded to V, Cn, Nr and Dp and the lowest (about 0.10) to H and Nm. Repeatability of the first ejaculate was greater than that of the second for pH, Mm, Mi, H, Dp and Dd.