153 THE EFFECT OF CONTINUOUS EXOGENOUS GONADOTROPIN TREATMENT ON OVARIAN ACTIVITY IN TIGERS (PANTHERA TIGRIS SPP.)

Abstract

Tigers are seasonally polyestrus, induced ovulators and can show breeding behavior for 7 days or more. The aim of this study was to determine the optimal time to trigger ovulation to induce a normal luteal phase. Previously, naturally cycling tigresses (n = 5) were observed for estrus and treated with gonadotropin-releasing hormone (GnRH) agonist. It appeared from ovarian laparoscopic examinations, fecal estrogen, and progesterone measurements, that Day 4 of estrus was optimal for timing the ovulation trigger. One of the tigresses had three 10 to 12 mm follicles and three ovulation sites on her ovaries and produced a live cub after intra-uterine laparoscopic artificial insemination using fresh semen. To control the cycle and further pinpoint the timing for ovulation, a study was conducted on three tigresses using purified pFSH, previously shown to be effective in tigers (Crichton et al. 2003 Biol. Reprod. 68, 105–113) delivered in an implantable osmotic pump (Alzet, Palo Alto, CA, USA) and GnRH agonist delivered on Day 4 of estrus. None of the females ovulated as determined by fecal progesterone measurements, which is consistent with previous anecdotal reports that GnRH agonists are effective in natural cycles but not in stimulated cycles in felids. To overcome this problem, a study was conducted on 6 tigresses (n = 11 cycles) using 210 mg pFSH (Folltropin-V, Bioniche, Belleville, ON, Canada) delivered at 1.25 U pFSH/h and the tigresses were treated on Day 4 of estrus (7 days after pFSH implantation) with 50 μg GnRH agonist (Cystorelin, Merial, Victoriaville, QC, Canada) in addition to 10 000 IU of hCG (Profasi, Serono, Rockland, MA, USA), the latter previously shown to be effective in felids (Donoghue et al. 1993 J. Zoo Wild. Med. 24, 185–189). Fecal samples were collected and analyzed for estradiol and progesterone and ovarian responses were examined laparoscopically. Results were compared using Student’s t-tests. Discrepancies in reported sample numbers were due to limited sample availability. Concentrations of fecal estradiol were similar (P > 0.05) between females treated with pFSH and natural cycles (172.5 ± 14.9 ng g^–1, n = 8 v. 204.8 ± 4.1 ng g^–1, n = 4; respectively). Females responded to hormonal stimulation with a significant increase (P < 0.05) in the number of large follicles (>9 mm) to CL stages compared to naturally cycling females (11.8 ± 1.9, n = 11 v. 4.0 ± 0.1, n = 5; respectively). There was no difference (P > 0.05) in the average duration of the luteal phase between stimulated and natural cycles (32.9 ± 0.1d, n = 7 v. 33.3 ± 1.4d, n = 3; respectively). Luteal phase progesterone concentrations were significantly higher (P < 0.05) after GnRH and hCG treatments than in naturally ovulating tigresses (6.3 ± 1.0 μg g^–1, n = 10 v. 2.8 ± 0.6 μg g^–1, n = 4; respectively). In summary, while follicular development was increased, exogenous hormone administration resulted in fecal estradiol concentrations and luteal phase duration similar to that of naturally cycling tigresses. Nevertheless, progesterone concentrations were significantly higher and follicular phase duration tended to be longer in the stimulated cycles.