Bull Semen Evaluation Post-thaw and Relation of Semen Characteristics to Bull’s Fertility

Evaluation of the quality of cryopreserved bull spermatozoa is reviewed. The methods for the assessment of sperm quality have markedly improved over the last decades – starting with the assessment of morphological shapes and subjective motility analysis towards the more sophisticated analysis of the molecular changes in chromatin, membranes and catabolic activities of the sperm cell itself. Function of sperm plasma membrane under the hypoosmotic conditions, distribution and concentration of ions, or function of different organelles seem to correlate with the degree of the viability of spermatozoa after freezing and thawing procedures. Many in vitro techniques that stimulate sperm function through female–derived factors, such as zona and oocyte, in zona pellucida binding assay, in vitro fertilization (IVF) and production of embryos, were employed to predict the outcome of artificial insemination in the field. Still, majority of methods used for semen analysis today are both tedious and expensive, and, in many cases confined to human bias. In order to increase the predictive power of assessment, simultaneous analysis of multiple sperm attributes, or outcomes of several laboratory assessments must be combined to look for the overall effect of several independent sperm parameters.