In vitro evaluation of sperm quality related to in vivo function and fertility.

The potential fertility of a sire can not be evaluated in the field simply by assessment of mating ability and physical examination, although these procedures can expose his limitations as a breeder. Finding a laboratory test that accurately estimates the potential fertility of a semen sample or a sire is also distant, as shown by the modest correlations that present tests have with fertility. Due to the complex nature of male fertility any sought for laboratory method must include testing of most sperm attributes relevant for both fertilisation and embryo development, not only in individual spermatozoa, but within a large, heterogeneous sperm population. Although such a task has proven difficult, it is both challenging and attractive for ruminants, where methods with good estimative power are available to evaluate the many attributes required for fertilisation. Among these methods are the isolation of highly viable spermatozoa by swim-up followed by their ability to respond to capacitation or acrosome reaction challenges and their capacity to penetrate homologous or heterologous zona pellucidae (ZP). Identification of fertility markers in, for instance, seminal plasma would further aid in identifying low-fertility sires. Future efforts should concentrate on finding how many spermatozoa in the semen sample are competent for fertilisation, perhaps by screening sperm linear motion, membrane integrity and membrane stability by multi-parametric methods, linked to the ability of males to provide a stable population of spermatozoa in a repeatable manner.