Ovine endometrial estrogen receptor expression is altered following PG-600 administration.

BACKGROUND: Dysregulation of the estrogen receptor 1 (ESR1) expression during the establishment of pregnancy could contribute to reduce fertility reported in ewes treated with PG-600. OBJECTIVES: The objective of this study was to evaluate the effect of treatment with PG-600 on ESR1 expression in the ovine endometrium during early diestrus. METHODS: Polypay ewes (n = 24) that had exhibited an oestrous cycle of normal duration (16-18 days) were treated with intravaginal progesterone-releasing device (CIDR) for 9 days. Cloprostenol was administrated two days before CIDR withdrawal. On the day of CIDR withdrawal (day 0), ewes received a 5 mL intramuscular injection of PG-600 (400 IU equine chorionic gonadotropin and 200 IU human chorionic gonadotropin) or saline. Blood samples were collected before treatment and on the day of tissue collection to determine serum estradiol-17ß and progesterone concentrations using radioimmunoassay. On days 4 and 7, six ewes from each treatment group were anaesthetised and a laparotomy was performed to obtain intercaruncular endometrial samples. Endometrial samples were collected ipsilateral to the ovary bearing the highest number of corpora lutea. An estradiol exchange assay was used to determine ESR1 concentration. RESULTS: Estradiol concentrations did not differ by time or treatment, but progesterone concentrations were significantly higher in the PG-600-treated group on day 7 despite a similar number of corpora lutea. Endometrial ESR1 concentration was significantly reduced on day 7 in the PG-600 group. CONCLUSIONS: In conclusion, although progesterone was higher than controls on day 7, ESR1 did not differ from controls suggesting that treatment with PG600 is unlikely to impair reproductive potential.

Estrus Synchronization in the Sheep and Goat.

Estrus synchronization and manipulation are a tool that has been used by producers to provide uniform lamb and kid meat production and dairy sheep and goat milk production, to concentrate work and labor cost, and to plan for the lambing and kidding time. Breeders can also use estrus synchronization to stimulate ewes and does to exhibit estrus and ovulate outside of the breeding season, although both the ovulation rate and pregnancy rate may be decreased. To increase the ovulation rate outside of the breeding season, a variety of estrus synchronization methods have been used.

Effect of different dosages of PG-600 on ovulation and pregnancy rates in ewes during the breeding season.

This study compared the reproductive effects of different dosages of PG-600 (Intervet/Merck Animal Health, Madison, NJ) during the breeding season of ewes. PG-600 is a single-dose injectable product labeled for estrous induction in swine, containing equine chorionic gonadotropin (80 IU/mL) and human chorionic gonadotropin (40 IU/mL). PG-600 is routinely used off-label for out-of-season estrous induction in sheep. However, at the most common dose administered to ewes (5 mL), PG-600 is likely to overstimulate the ovaries, resulting in reduced pregnancy rates. Following estrous synchronization with intravaginal progesterone and cloprostenol, Polypay ewes were treated with 5 mL PG-600 (T1; n = 8), 1.5 mL PG-600 (T2; n = 8), or 5 mL saline (C; n = 8) and then mated to rams. Jugular vein samples were collected prior to the PG-600 injection (0 hr) and at 2, 4, 8, 12, and 24 hr after injection. Serum estradiol-17ß was determined by chemiluminescence and among groups using repeated measures analysis of covariance. Ovulation and pregnancy rates were determined by transrectal ultrasonography and compared by one-way ANOVA and chi-square, respectively. Estradiol-17ß concentrations were greater in T1 compared to T2 and C (P < 0.001). Ovulation rate was greater (P < 0.001) but pregnancy rate was lower (P < 0.001) in the T1 compared to C and T2. These data confirm that a 5 mL dose of PG-600 administered to ewes during the breeding season overstimulates the ovaries, which may then reduce fertilization or embryo survival. Future research will focus on the effects of different dosages of PG-600 on pregnancy rate of ewes during the nonbreeding season.