Measurement of plasma oestradiol after an injection of a gonadotrophin as a test for neutered bitches

Twenty-eight bitches with unknown reproductive histories were injected intr avenously with either human chorionic gonadotrophin (hcc) or equine chorion ic gonadotrophin (eCG) (pregnant mare's serum gonadotrophin) and their oest radiol responses were measured at the time of the injection and 90 minutes later. They were at various stages of the oestrous cycle as determined by h istology and a progesterone assay for luteal function. Twenty-six of them w ere considered to be entire because they showed either an increase in plasm a oestradiol over preinjection values or steady high values. The ovaries we re removed from 25 of these animals and the other probably had a remnant of ovary because it came into oestrus some weeks later. In two remaining bitc hes no oestradiol could be detected either before or after the injection of gonadotrophin and they were predicted to have been neutered, which was con firmed at laparotomy. in the entire bitches, the highest plasma oestradiol concentration was measured during metoestrus and the lowest during anoestru s.