213 THE EFFECT OF eCG TREATMENT IN AN ESTRUS SYNCHRONIZATION PROTOCOL ON PREGNANCY RATES AFTER EMBRYO TRANSFER IN HOLSTEIN HEIFERS

Abstract

Recent studies have shown that the presence of accessory or multiple corpora lutea (CL) and increased progesterone (P4) concentrations reduced early embryonic mortality in cattle. The objective of this study was to evaluate the effect of equine chorionic gonadotropin (eCG) treatment on the number of CL, the P4 concentrations, and pregnancy rates after embryo transfer (ET). Holstein heifers (n = 120) from 7 dairy farms received an intravaginal progesterone-releasing device (CIDR; InterAg, Hamilton, New Zealand) and 2 mg IM of estradiol benzoate (EB; Gynandol®; Sankyo, Tokyo, Japan) at random stages of the estrous cycle. After 7 to 9 days, CIDRs were removed and 15 mg of prostaglandin F2α (PG; Pronalgon®; Pfizer Japan, Nagoya, Japan) were administered, followed by 100 µg IM GnRH (Conceral®; Takeda Pharmaceutical Co., Ltd., Osaka, Japan) 2 days later (Day 0). The heifers were placed at random into 3 groups for eCG treatment. The eCG was not administered in a control group (n = 53); heifers in other 2 groups received 1000 IU eCG (Peamex®; Sankyo, Japan) IM at the time (0 h group, n = 37) or 48 h before (48 h group, n = 30) PG injection/CIDR removal. On Day 7, heifers were examined by ultrasonography (Aloka SSD500; Aloka, Tokyo, Japan) for number of CL; heifers with at least one functional CL received an in vivo-derived frozen–thawed embryo by direct transfer. At the same time, a blood sample was collected to determine P4 concentration. Pregnancy rates were determined on Days 30 and 60 by ultrasonography and rectal palpation, respectively. The data were analyzed by ANOVA and means were compared with Fisher's PLSD. Proportional data were analyzed by the chi-square test. P4 concentrations (mean ± SD) on Day 7 were 1.8 ± 1.0, 5.6 ± 3.3, and 2.2 ± 1.1 ng mL−1 for the control, 48 h, and 0 h groups, respectively (48 h vs. control and 0 h; P < 0.001). The number of CL on Day 7 were 1.1 ± 0.4, 2.5 ± 1.4, and 1.8 ± 0.9 for the control, 48 h, and 0 h groups, respectively (control vs. 48 h and 0 h, and 48 h vs. 0 h; P < 0.01). Pregnancy rates did not differ between 0 and 48 h groups but both were higher than in the control group (Table 1). Results suggest that the estrus synchronization protocol with administration of eCG at the time of CIDR removal or 48 h earlier significantly increased the number of CL and the P4 concentration, and improved pregnancy rates in Holstein heifers after ET. Table 1.Pregnancy rates of Holstein heifers synchronized with CIDR and PG and treated with eCG