Evaluation of human chorionic gonadotropin as a replacement for gonadotropin-releasing hormone in ovulation-synchronization protocols before fixed timed artificial insemination in beef cattle1

Abstract

Two experiments were conducted during 2 yr to evaluate differences in ovulation potential and fertility in response to GnRH or hCG. In Exp. 1, 46 beef cows were given 100 microg of GnRH or 500, 1,000, 2,000, or 3,000 IU of hCG. Ovulation incidence was not different between GnRH and any of the hCG doses, indicating that ovulatory capacity of at least 500 IU of hCG was equivalent to GnRH. In Exp. 2, beef cows (n = 676) at 6 locations were assigned randomly to a 2 x 3 factorial arrangement of treatments. Main effects were: 1) pre-timed AI (TAI) treatment (GnRH or hCG) and 2) post-TAI treatment (saline, GnRH, or hCG) to initiate resynchronization of ovulation in previously inseminated cattle. Blood samples were collected (d -21 and -10) to determine progesterone concentrations and assess cyclicity. Cattle were treated with a progesterone insert on d -10 and with 100 microg of GnRH or 1,000 IU of hCG. A PGF(2alpha) injection was given at insert removal on d -3. Cows were inseminated 62 h (d 0) after insert removal. On d 26 after first TAI, cows of unknown pregnancy status were treated with saline, GnRH, or hCG to initiate a CO-Synch protocol. Pregnancy was diagnosed 33 d after first TAI to determine pregnancies per AI (P/AI). Nonpregnant cows at 6 locations in yr 1 and 1 location in yr 2 were given PGF(2alpha) and inseminated 56 h later, concurrent with a GnRH injection. Five weeks later, pregnancy diagnosis was conducted to determine pregnancy loss after first TAI and pregnancy outcome of the second TAI. Injection of pre-TAI hCG reduced (P < 0.001) P/AI compared with GnRH, with a greater reduction in cycling cows. Post-TAI treatments had no negative effect on P/AI resulting from the first TAI. Serum progesterone was greater (P = 0.06) 7 d after pre-TAI hCG than after GnRH and greater (P < 0.05) after post-TAI hCG on d 26 compared with saline 7 d after treatment in association with greater frequency of multiple corpora lutea. Compared with saline, injections of post-TAI GnRH and hCG did not increase second insemination P/AI, and inconsistent results were detected among locations. Use of hCG in lieu of GnRH is contraindicated in a CO-Synch + progesterone insert protocol. Compared with a breeding season having only 1 TAI and longer exposure to cleanup bulls, total breeding season pregnancy rate was reduced by one-third, subsequent calving distribution was altered, and 50% more AI-sired calves were obtained by applying 2 TAI during the breeding season.

Roles of hCG in Advancing Follicular Growth to Ovulation after Concurrent Injections of and GnRH in Postpubertal Holstein Heifers Bearing a CL

“…Our results agree with data reported by researchers [17] who induced ovulation in women, beef cows [30], and dairy heifers [32] treated with hCG injections. In addition, our data is also in line with research findings which suggest that hCG selectively stimulates folliculogenesis and induces ovulation in women [33].…”

“…These investigators concluded that progesterone reduced the ability of endogenous or exogenous estradiol to induce a preovulatory LH surge and ovulation. Furthermore, other investigators reported that cows with progesterone concentrations greater than 1 ng/ml before treatment with either hCG or GnRH tend to ovulate less often than those having progesterone levels below 1 ng/ml [30]. Nevertheless, the group receiving the PGF + GnRH + hCG treatment in the present study ovulated earlier than the other two experimental groups even though progesterone levels were higher (3.78 ± 1.34) than 1 ng/ml.…”

Administration of human chorionic gonadotropin to suckled beef cows before ovulation synchronization and fixed-time insemination: Replacement of gonadotropin-releasing hormone with human chorionic gonadotropin1

“…The capacity of hCG to induce ovulation of small follicles has been reported (Burns et al, 2008;Stevenson et al, 2008b). Ovulation of small follicles may result in poorer fertility possibly because of a resulting smaller CL with a decreased capacity to produce P4 (Vasconcelos et al, 2001).…”

“…When hCG was administered to beef cows, CL development resulted from follicles <10 mm in diameter (Sheffel et al, 1982) and 6 of 18 Iactating dairy cows treated with hCG having follicles <10 mm in diameter ovulated compared with 0 of 13 treated with GnRH (Buttrey et al, 2010). In addition, beef cows receiving 1,000 IU of hCG tended to have greater concentrations of progesterone (P4) 7 d after treatment than those receiving GnRH (Burns et al, 2008). Thus, hCG may have greater capacity to luteinize preovulatory follicles compared with GnRH (Schmitt et al, 1996b).…”

Association of pregnancy per artificial insemination with gonadotropin-releasing hormone and human chorionic gonadotropin administered during the luteal phase after artificial insemination in dairy cows: A meta-analysis

“…No difference in the nature of the treatment (hCG or GnRH) was observed. The GnRH and hCG treatments have similar effects on the ovary (Fricke et al, 1993), induction of ovulation (Burns et al, 2008), and formation of accessory CL (Schmitt et al, 1996b).…”