Selection for boar fertility and semen quality--the way ahead

Critical needs for the swine industry in terms of boar fertility evaluations are validation of semen quality estimates with in vivo reproductive data; estimation of the relative fertility of boars; and elimination of sub-fertile ejaculates. Single sire matings are the best way to validate semen quality estimates with reproductive performance. Sampling about 20% of the population provides an accurate estimation of the variability among boars and should be sufficient for this purpose. In vitro tests that measure univariate characteristics of ejaculates including motility and morphology appear to be just as accurate as those that measure multivariate traits such as in vitro fertilization in terms of predicting boar fertility. Reasons for this observation may be related to how properties of sperm cells are influenced by the sow reproductive tract. Several seminal plasma proteins show strong correlations with boar fertility and hold potential for being developed into tests that can rank the relative fertility of boars. Almost 90% of the variation in boar fertility was explained when the proportion of motile and acrosome-reacted spermatozoa was combined with relative amounts of 28 kDa, pl 6.0 and 55 kDa, pl 4.5 seminal plasma proteins. Consequently, combining different complementary tests improves estimations of boar fertility. Motility estimates routinely performed in most A.I. centres are a reasonable technique for identification and elimination of sub-fertile ejaculates. However, the accuracy with which they currently are conducted within the swine industry needs improvement.