Enhancing pregnancy rates in bovine embryo recipients: How equine (eCG) and human (hCG) chorionic gonadotropins...

We compared the effects of hCG and eCG treatment on CL development and pregnancy per embryo transfer (P/ET) in beef cows. In Exp.1, non-lactating Nelore cows received either no treatment (Control, n = 13) or 500, 1000, or 2000 IU hCG (n = 12-13/group) two days after ovulation. Luteal area (LA), blood perfusion (BP), and P4 levels were measured for 14 days. In Exp.2, primiparous crossbred cows (n = 889) subjected to a P4/E2 protocol on Day 0 (D0) were assigned to Control (300 IU eCG on D9), eCG/2x (150 IU eCG on D7 and D9), hCG (300 IU eCG on D9 +1000 IU hCG on D14), or eCG/2x+hCG groups. Dominant follicle (DF) size, LA, BP, and P4 were measured, and fresh blastocysts were transferred on D18. In Exp.1, accessory CL (aCL) rate differed (P < 0.05) among treatment groups (C, 0 %^C; hCG-500, 8 %^BC; hCG-1000, 61.5 %^A; hCG-2000, 41.6 %^AB). Total LA was greater (P < 0.05) in hCG-1000 and hCG-2000 than in Control. BP did not differ significantly (P > 0.1). P4 concentration was higher (P = 0.04) from day 6-12 in the hCG-1000 and hCG-2000 groups. In Exp.2, eCG/2x increased DF size (P = 0.07), and combined hCG and eCG/2x treatments increased LA (P < 0.01). Combining hCG with eCG/2x; however, reduced BP (P = 0.01). P/ET was higher (P = 0.01) in eCG/2x and hCG groups than in Control at 28- and 60-150-days post-ET. In conclusion, ≥ 1000 IU hCG improves LA, P4, and P/ET but not BP. Administering eCG twice enhances DF and P/ET but combining eCG and hCG is not suggested due to reduced BP without further improving P/ET.