Relationships among in vivo fertility, computer-analysed motility and in vitro Ca²⁺ flux in bovine spermatozoa

Abstract

Correlations among computer-assisted spermatozoa motility analyses, Ca 2+ fluxes and in vivo fertility of bovine spermatozoa based on a total of 4482 inseminations were investigated in each of four ejaculates from six bulls. The Ca 2+ parameters assessed the rate of change in intra- and extracellular Ca + in fresh and cryopreserved spermatozoa from the same ejaculates and were described in another study. Of the seven motility parameters of cryopreserved semen investigated, all differed significantly among bulls but none were related to the in vivo fertility of cryopreserved semen. The amplitude of lateral head displacement, a motility parameter associated with hyperactivation, was positively correlated with the intracellular Ca 2+ levels and the rate of Ca 2+ accumulation of cyropreserved spermatozoa. The highest fertility was observed when initial extracellular Ca 2+ for cryopreserved spermatozoa was high and when Ca 2+ efflux rates of cryopreserved cells approached the higher efflux rates of fresh spermatozoa. Fertility was reduced when cryopreserved spermatozoa had initial internal Ca 2+ levels greater than those of fresh spermatozoa or when cryopreserved spermatozoa internalized Ca 2+ rapidly. Calcium flux, but not motility, may predict fertilizing capacity of cryopreserved bovine spermatozoa. Key words: Calcium, computer-analysed motility, fertility, spermatozoa, bull