174 COMPARISON OF ORAL ALTRENOGEST, CIDR, AND LONG-ACTING PROGESTERONE FOR SYNCHRONIZATION OF ESTRUS IN MARES

Abstract

Synchronization of oestrus in mares remains a challenge to practitioners using Assisted Reproductive Technologies. The research objective was to compare adverse reactions and reproductive parameters in mares treated with different sources of progestins for oestrus synchronization. Mixed breeds of mares with a mean age of 3 years (range 2–20) were used. Groups were: 1) altrenogest 0.044 mg kg^–1 BW PO daily for 10 days (D) (Regumate, Merck, White House Station, NJ, USA) (n = 30), 2) Long-acting progesterone (LAP4) (BET Pharmacy, Lexington, KY, USA) (n = 30) 10 cc IM once in the neck, and 3) Controlled intravaginal drug release (CIDR-B 1.9 g P4; Zoetis, Kirkland, QC, Canada) (n = 15) vaginal insert for 10 days. Mares were randomly assigned to treatment and evaluated using transrectal reproductive ultrasonography on Days 1 (treatment initiation), 5, 10, and daily during oestrus until ovulation (Ov). On Day 10, mares were given 250 µg of cloprostenol (PG) (Estrumate, Merck) IM, and when a follicle (F) >35 mm was detected 2500 IU hCG (Chorulon, Intervet, Millsboro, MD, USA) was administered IM. Adverse reactions were scored as follows: Regumate – any reaction at any time; LAP4 – the injection site was inspected and scored as: 0, no reaction; 1, mild slight raised area; 2, moderate reaction 5 cm; 3, severe reaction 6–10 cm; 4, very severe reaction >10 cm on Day 5 post-injection; CIDR categorical scores were: 0, no discharge; 1, mild vaginal discharge on CIDR at withdrawal; 2, moderate discharge on tail or vulva; 3, severe urine scald or visible discharge; 4, very severe thickened inflamed skin from urine scald or discharge. Chi-squared test at P < 0.05 was used to evaluate the overall frequency of reactions in mares, and the presence of intrauterine fluid. The time from cloprostenol (PG) to F 35, hCG to Ov, PG to Ov, and mm of intrauterine fluid on Days 1–3, was evaluated using the Shapiro–Wilk test and Kruskall–Wallis at P < 0.05. Results of the overall adverse reactions were: Group 1 0/30 (0%), Group 2 9/30 (30%), and Group 3 14/15 (93.3%). The Group 2 treatment resulted in category 0–4 reactions as follows (21/30, 1/30, 5/30, 2/30, 1/30) and for Group 3 category 0–4 (1/15, 13/15, 0/15, 1/15, 0/15), respectively. The overall frequency of adverse reactions was significantly different between groups (P = 0.0000) with Group 2 having the highest rate. Reproductive parameter results were median (quartiles) days from PG to F35 for groups 1–3 respectively: 4 (2.8–6), 5 (0–6), 3 (4–6), hours from hCG to OV: 42(42–42), 42 (42–72), 42 (43–54); and days from PG to OV: 8 (4.5–8), 8 (5–8), 6.6 (4.8–8). Fluid Day 1, Day 2, Day 3 had a median of 0 mm on all days, and on Day 3 mm of fluid was mild 0 (0–0.125) but different between groups (P = 0.0379). The detection of intrauterine fluid on Day 2 (P = 0.005) was different between groups. No follicle wave synchronization was achieved by progestin administration; hence, the main differences noted between groups were the frequency of adverse reactions, rather than the reproductive parameters studied. The cost of the treatment and the frequency of adverse reactions are important considerations when choosing an oestrus synchronization therapy for mares.

Research was supported by the Alberta Agriculture Research Institute.