104  Induction of cyclicity in seasonally anestrous recipient mares

Anestrous (AN) recipient mares’ natural cyclicity must be manipulated to produce foals from transferred embryos early in the year. One approach uses sulpiride to stimulate prolactin (PRL) that appears to have an important reproductive role effecting seasonality in mares. While previous research utilized sulpiride to induce ovulation (OV) in AN mares, few have transferred embryos after treatment. This study was designed to evaluate the effect of a treatment of estradiol cypionate (ECP) and sulpiride on inducing OV and subsequent pregnancy outcome in AN recipient mares of various reproductive status performed on a commercial embryo transfer farm. Anestrous recipient mares (n = 32) were randomly assigned to 4 treatment groups based on records of ovarian activity. Transitional (T, n = 8), AN (n = 11), and progesterone pre-treated (P, n = 9, received 4 mg altrenogest IM 3 wk prior) groups were treated January 20 with 50 mg of ECP IM and 3 g of sulpiride IM 24 h later. A control group (C, n = 4) of AN mares received the carrier. Jugular blood samples were collected at 0, 3, 6, 12, and 24 h post-treatment followed by daily collection for 10 d and collection every other day for 32 d thereafter and analyzed for luteinizing hormone (LH) and PRL. Ovaries were transrectally scanned every 2 to 3 d for 60 d. Embryos were transferred to 10 mares (5 T, 3 P, 2 AN) after at least the second estrous cycle up to the sixth cycle depending on their synchrony to the donor. Binomial data was analyzed via PROC GLIMMIX of SAS, and number of days to OV and hormonal data were analyzed via PROC MIXED with repeated measures. Nonparametric data were natural log-transformed and analyzed if normality was improved. Differences of least squares means were determined using the PDIFF option in SAS with ∝ ≤ 0.05 used to declare significance. There was an effect of treatment on the number of mares that achieved first OV (P < 0.001) with 23 of 28 (82.1%) treated mares having a first OV within 22 d of treatment; and second OV (P = 0.018) with 15 of the 23 (65.2%) mares that had a first OV achieving a second OV within 43 d. The mean number of days to first OV of T, AN, and P groups together were 32 ± 5 d earlier (P < 0.001) than C. The transitional group ovulated sooner (P = 0.05) than AN and tended (P = 0.07) to ovulate sooner than P. There was an effect of the treatment-by-day interaction on plasma mean PRL (P < 0.001) and LH (P = 0.021) concentrations. Of the 10 embryos that were transferred, 7