365 THE EFFECT OF ADMINISTERING PROGESTERONE AND ESTRADIOL PRIOR TO eFSH ON THE SUPEROVULATORY RESPONSE OF MARES

Abstract

eFSH has been used to induce multiple ovulation in cycling mares. However, the response to eFSH is variable. Generally, eFSH is initiated 5 to 7 days after ovulation at a time when the follicular population on the ovaries may be variable. The objective of this study was to determine whether administration of progesterone and estradiol for 10 days prior to eFSH (Bioniche Animal Health, Athens, GA) would enhance the response to eFSH administration. Thirty normal cycling mares were assigned to 1 of 2 groups. Group 1: Control eFSH treatment - mares were examined daily with ultrasonography beginning 5 days after ovulation. Once the follicles in these mares reached 20 to 25 mm in size, eFSH treatment (12.5 mg, i.m.) was administered twice a day. Cloprostenol (Schering-Plough, Union, NJ, USA) treatment (250 ¼g) was administered on the second day of eFSH treatment. eFSH treatment continued until the majority of the cohort of follicles reached e35 mm. Treatment was stopped and after approximately 36 h hCG (2500 IU, i.v.; Chorulon; Intervet, Millsboro, MD, USA) was administered. Group 2: Injectable progesterone + estradiol (150 mg of progesterone and 10 mg of estradiol; P+E) treatment was initiated in diestrus (5 to 7 days post-ovulation) for 8 mares and in early estrus for 7 mares in this group. Injectable progesterone was continued for 10 days and Cloprostenol (250 ¼g) was administered on Day 10. Mares were then examined daily with ultrasonography and, once they had acquired 20- to 25-mm follicles, eFSH treatment was initiated. Twice-daily injections of eFSH (12.5 mg, i.m.) were continued until a majority of the cohort of follicles was e35 mm. hCG was administered approximately 36 h later. All mares were inseminated with 1 billion progressively motile spermatozoa from one of two stallions on the day of hCG administration and on the following day with cooled semen (1 billion progressively motile spermatozoa) from the same stallion. Data were analyzed by t-test and Fisher's Exact Test. The number of days of eFSH treatment was similar for the P+E (2) vs. the control (1) group (4.2 ± 2.0 vs. 4.9 ± 1.3 days, respectively). However, the number of ovulations induced in response to eFSH was greater for mares in the eFSH control (1) group (5.6 ± 2.0) than for those in the P+E (2) group (3.0 ± 1.9). Embryo recovery per flush was also greater for eFSH control (1) mares (2.7) vs. P+E (2) mares (1.1). Embryo quality was excellent or good for all embryos in both groups. Seventy-three percent of the mares (11 of 15) in both groups gave at least one embryo at each recovery attempt. However, more mares in the eFSH control (1) group gave two or more embryos (60%) compared to those in the P+E (2) group (20%). In summary, treatment of mares with P+E prior to eFSH treatment resulted in fewer ovulations, fewer embryos recovered, and fewer mares providing e2 embryos. Thus, there was no advantage in pretreating mares with P+E prior to eFSH treatment.