INFLUENCE OF BOVINE AMPULLARY AND ISTHMIC OVIDUCTAL FLUID ON SPERM-EGG BINDING AND FERTILIZATION IN-VITRO

The objective of this study was to determine the effects of oviductal fluid on sperm binding and fertilization in vitro when either bovine o ocytes or both spermatozoa and oocytes are incubated in fluid from dif ferent regions of the oviduct and at different stages of the oestrous cycle. Oocytes, or oocytes and spermatozoa, were incubated in nonlutea l and luteal oviductal fluid obtained from the whole, isthmic or ampul lary oviduct of dairy cows. Gametes were washed and coincubated in fer tilization medium for 18 h, and then observed for sperm binding and pe netration. More spermatozoa bound to oocytes that were preincubated in nonluteal oviductal fluid than to those that were incubated in luteal oviductal fluid; however, there were no differences in fertilization rates between the two treatments. More spermatozoa bound to oocytes in cubated in isthmic than in ampullary oviductal fluid. However, if both gametes were incubated in oviductal fluid before their coincubation, binding was higher when both gametes were incubated in ampullary ovidu ctal fluid. By reducing the time of coincubation of spermatozoa with t he oocytes, differences in fertilization rates were seen among the var ious oviductal fluid treatments. At 14 and 16 h of coincubation, more oocytes were fertilized if spermatozoa were preincubated in isthmic ov iductal fluid and oocytes were preincubated in ampullary oviductal flu id than if both gametes were incubated in whole or ampullary oviductal fluid. Because both sperm binding to the zona pellucida and fertiliza tion rates were greater in treatments in which gametes were exposed to regional oviductal fluid than when they were incubated in whole ovidu ctal fluid, it is concluded that oviductal fluid from different region s of the bovine oviduct may play different roles in facilitating ferti lization.