Sperm-associated seminal plasma proteins - a novel approach for the evaluation of sperm fertilizing ability of stallions?

Mammalian cysteine-rich secretory proteins (CRISP) are characterized by 16 cysteine residues forming 8 disulfide bonds. In the horse male genital trac t CRISP proteins have been identified in the testis (CRISP-2), in the epidi dymis (CRISP-1) and in the ampulla (CRISP-3). Using a monospecific avian an tibody that recognizes all equine members of the equine CRISP family, CRISP proteins have been immunolocalized at the postacrosomal region of the sper m head and the tail midpiece being associated to the sperm surface during e pididymal transit. CRISP's appear to be tightly bound to the sperm surface surviving the passage through the female genital tract, in vitro capacitati on and acrosome reaction and extensive washing at high salt concentrations. The number of CRISP molecules tightly bound to the sperm surface could be determined by means of a competitive inhibition ELISA assay and have been s hown to correlate (p less than or equal to 0.069, Pearson correlation)/ to correlate significantly (p < 0.01, Spearman rank correlation analysis) with the fertility of stallions. Protein concentration of more than 18000 molec ules/ sperm cell correlates with good pregnancy and foaling rates. Together with conventional sperm parameters, e.g. progressive motility and sperm co ncentration, the biochemical marker (CRISP molecules/ sperm cell) allows a better prediction (R-2 = 0.54, p< 0.02) of the stallion fertility rate in v ivo and is alternative to other functional tests such as the expensive and time-consuming hemizona assay.