18OVARIAN SUPPRESSION WITH THE PROGESTIN LEVONORGESTREL IMPROVES OVULATION INDUCTION FOR ARTIFICIAL INSEMINATION IN THE DOMESTIC CAT

Abstract

Ovarian response to gonadotropin stimulation for artificial insemination (AI) is variable in the domestic cat. After ovulation induction with gonadotropins, a secondary wave of corpora lutea (CL) is often produced that alters endocrine profiles. This study assessed the impact of ovarian suppression with the progestin, levonorgestrel, before ovarian stimulation with equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG) on ovarian response in the cat. Queens were assigned randomly to: 1) levonorgestrel (LNG), 6 Norplant® rods implanted for 37d+eCG/hCG (n=6cats); and 2) Control, eCG/hCG alone (n=6). Ovarian response was graded (scale 1–4; 1=excellent, 4=ovulation failure) 36–40h post hCG (Day 5) using laparoscopy. Ovariohysterectomy (OVH) was performed on Day 23 and CL number and CL progesterone (P) content determined. Fecal samples were collected daily and metabolites of estradiol (E) and P quantified from >60d before inhibition through OVH. Estrus and luteal activity were defined as fecal E and P concentrations greater than two or three times baseline, respectively. Time data were analyzed using repeated measures analysis and remaining data were analyzed using ANOVA. LNG abolished ovarian activity in all cats. No E peaks were observed during LNG inhibition compared with pre-inhibition (mean±SEM; 1.8±0.3 peaks/37 days). In contrast, number of E peaks pre- v. during inhibition was similar (P>0.05) in control (pre, 2.2±0.3; during, 2.0±0.0) cats. All LNG cats had baseline E and P concentrations at eCG administration. Conversely, three of six control cats had elevated E and two cats had elevated P concentrations when eCG was given. Ovarian grade was higher (P<0.05) in LNG (1.3±0.2) v. control (2.9±0.4) cats. All LNG cats had ≤Grade 2 responses, whereas two control cats failed to ovulate (Grade 4) or had mature CL (Grade 3) at laparoscopy. For both LNG and control cats, mean peak E (overall mean, 117.4±14.4ngg−1 feces) was higher (P<0.05) and duration of estrus (6.8±0.9d) was longer (P<0.05) after eCG/hCG v. pre-inhibition values (81.4±5.3ngg−1 feces and 3.9±0.3d, respectively). However, P concentrations/luteal phase were higher (P<0.05)after eCG/hCG v. pre-treatment CL in control but not LNG cats. In cats with an ovarian grade of ≤2, control cats had more (P<0.05) CL at Day 23 (14.0±2.9CL/cat) compared to Day 5 (4.5±0.5).LNG cats showed no (P>0.05) accessory CL development on Day 23 (9.2±1.9CL/cat)compared to Day 5 (6.5±1.8). CL P content was not different (P>0.05) across treatments (overall mean, 90.8±18.7ngCL). Results show that inhibition of ovarian activity with levonorgestrel before eCG/hCG improves ovarian response and alleviates accessory CL development in the domestic cat.