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

Abstract

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-17β 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-17β 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.

Ovine endometrial estrogen receptor expression is altered following PG‐600 administration

“…In conclusion, this is the first report to examine the effect of PG-600 on ovine uterine ESR1 concentrations. Because PG-600 use in ewe has been associated with reduced fertility (Cross et al, 2019;Habeeb et al, 2019;Lunstra & Christenson, 1981), the results presented in this report demonstrate that uterine changes in ESR1 during the first week postoestrus after treatment are comparable to those found in normal cycling ewes. In conclusion, it appears unlikely that any of the observed changes in uterine ESR1 and estradiol and progesterone production after PG-600 treatment of ewes would impair their reproductive potential.…”

“…PG‐600 (Intervet/Merck Animal Health, Madison, NJ, USA) contains 80 IU/mL of equine chorionic gonadotropin (eCG) and 40 IU/mL of human chorionic gonadotropin (hCG). Our laboratory reported that PG‐600 administered to cycling ewes resulted in elevated serum estradiol‐17β concentrations within the first day after administration of PG‐600 and reduced pregnancy rates (Habeeb et al., 2019 ).…”

Effect of progesterone infused controlled internal drug releasing (CIDR) device and timing of gonadotropin stimulation using P.G. 600 on reproductive success in ewes bred out of season

“…An effort to characterize the impact of a common dose of P.G. 600 (5 mL, also the labeled dose for gilts and sows) revealed a decrease in pregnancy rates in ewes receiving 5 mL (400 IU PMSG and 200 IU hCG) compared with those receiving 1.5 mL (120 IU PMSG and 60 IU hCG; Habeeb et al, 2019 ). The dose of P.G.…”

Estrous synchronization in cattle, sheep and goat

“…For many years, sheep and goat farmers have used PG-600 to induce estrous during out-of-season estrous. The dosage that is most frequently mentioned in the literature, 5 mL per ewe, has been observed to overstimulate the ovarian tissue (Habeeb et al 2019), resulting in unusually big mature, large follicles and higher estradiol-17b concentrations at the time of ovulation (Safranski et al 1992).…”