LH-RELEASE, INDUCTION OF ESTRUS AND FERTILE OVULATIONS IN RESPONSE TOPULSATILE ADMINISTRATION OF GNRH TO ANESTROUS DOGS

In one study in 33 bitches, in which each of seven doses of GnRH were injected into six anoestrous bitches each, doses of greater than or eq ual to 400 ng kg(-1) released LH consistently, and doses of less than or equal to 200 ng kg(-1) did not. In a second study, GnRH was adminis tered in pulses of 15-500 ng kg(-1) every 90 min for 7-9 days to 36 an oestrous bitches, four prepubertal bitches and three luteal phase bitc hes. In 36 anoestrous bitches, GnRH pulses resulted in pro-oestrus, oe strus, ovulation and pregnancy in 26, 20, 16 and 12 bitches, respectiv ely. Mean time for pro-oestrus onset, oestrus, ovulatory LH surge and parturition were 5.1 +/- 0.4, 11.2 +/- 0.7, 14.0 +/- 9.0, and 77.3 +/- 1.0 days, respectively, from start of treatment. In response to GnRH, pro-oestrus and pregnancy occurred in two of four prepubertal bitches , and pro-oestrus but not ovulation occurred in one of three luteal ph ase bitches. Efficacy in anoestrous bitches was dose dependent with hi gh doses of > 280 ng kg(-1) (n = 12) versus intermediate 85-270 ng kg( -1) (n = 12) and low < 85 ng kg(-1) doses (n = 12) resulting in a high er incidence of pro-oestrus (100 versus 80 and 33%), oestrus (92 versu s 50 and 25%), ovulation (84 versus 42 and 8%) and pregnancy (58 versu s 33 and 8%). With few exceptions, failed or weak responses were relat ed to inadequate LH release, as measured in frequently collected sampl es following successive pulses on selected days of treatment; vaginal cornification, oestrous behaviour, and LH response were similar in oes trus without ovulation and fertile oestrus except for the lack of an o vulatory LH surge.