Mares were inseminated during 3 oestrous cycles with 1 10 ( 9 ) nonviable spermatozoa and 1 ) no additional treatment ( control ) , or in combination with 2 ) dexamethasone ( 50mg i.v. ) at the time of insemination , or 3 ) with mycobacterial cell wall extract ( 1.5 ml i.v. ) administered 24h prior to insemination .