Acrosome Morphology of Boar Spermatozoa Incubated before Cold Shock1

Abstract

Two experiments were conducted to determine the influence of cold shock on acrosome morphology and motility of boar spermatozoa. Acrosome morphology was assessed by phase-contrast microscopy of unfixed, unstained spermatozoa at 1560x. Acrosome morphology was differentially categorized into five classes, i.e., normal apical ridge (NAR), normal apical ridge with particles (NAR'), damaged apical ridge (DAR), missing apical ridge (MAR) and loose acrosomal cap (LAC). Boar spermatozoa with DAR and MAR acrosome alterations were observed to exhibit progressive motility. Experiment 1 was conducted using unextended boar semen. Sperm acrosomes were altered and sperm motility was reduced by cold shock at 0, 5, 10 and 15 C for 10 minutes. Sperm acrosomes developed cold shock resistance during 2.5 and 4.5 hr. incubation at 30 C. Acrosomes of whole ejaculate spermatozoa were more susceptible to cold shock than acrosomes of sperm rich fraction. In experiment 2, acrosomes of spermatozoa extended in Tris-lactose, citrate and saline solutions developed cold shock resistance during 3- and 5-hr, incubation at 30 C. Cold shock resistance was not developed, however, when boar spermatozoa were incubated in glucose-bicarbonate and IVT extenders for 3 and 5 hours.