Human chorionic gonadotropin (hCG)-induced ovulation occurs later but with equal occurrence in lactating dairy cows: comparing hCG and gonadotropin-releasing hormone protocols

Abstract

This study assessed the effects of two hormones, human chorionic gonadotropin (hCG) and gonadotropin-releasing hormone (GnRH), on ovulatory responses during different diestrous stages in lactating dairy cows. Estrous cycles of 21 cows were synchronized and were enrolled in stage 1 of the experiment. The cows were treated with a prostaglandin (PG) F2α analog either 9 to 10 days [mid-diestrus (MD) group] or 5.5 to 6.5 days [early-diestrus (ED) group] after synchronized ovulation (day 0 = first PGF2α administration). On day 2, the cows were administrated 250 μg GnRH or 3000 IU hCG. Ovulation was determined every 2 h from 24 to 36 h after GnRH or hCG administration, and then every 4 h up to 72 h until ovulation. Cows in stage 2 were administered these treatments in the reverse order. The results indicated that average ovulation times in cows treated with GnRH in the MD group (GnRH-MD group) and cows treated with GnRH in the ED group (GnRH-ED group) were 30.0 ± 1.0 h and 28.8 ± 0.4 h, respectively. However, ovulation times for cows treated with hCG in the MD group (hCG-MD group) and cows treated with hCG in the ED group (hCG-ED group) were 35.8 ± 4.6 h and 32.8 ± 2.2 h, respectively, and ovulation occurred significantly later in the hCG-treated groups than in the GnRH-treated groups. In summary, we found that hCG-induced ovulation occurred later than GnRH-induced ovulation regardless of different diestrous peroids; however, the two treatments did not differ in terms of percentage of ovulation.

Replacing the first gonadotropin-releasing hormone treatment in an Ovsynch protocol with human chorionic gonadotropin decreased pregnancies per artificial insemination in lactating dairy cows

“…By contrast, cows treated in early diestrus (i.e., 5.5-6.5 d after ovulation) ovulated earlier in both treatments (28.8 ± 0.4 h and 32.8 ± 2.2 h for GnRH and hCG, respectively). Independent of the stage of the estrous cycle, cows treated with GnRH ovulated earlier than cows treated with hCG (Liu et al, 2019).…”

“…Based on a distribution of time from treatment to ovulation (Figure 2), no cows in either treatment ovulated within 24 h after treatment, and there was overlap in time to ovulation between treatments. Liu et al (2019) reported time from treatment to ovulation after treatment of dairy cows with GnRH (250 µg of gonadorelin) and 3,000 IU of hCG to be 29.3 ± 0.5 h and 34.3 ± 2.5 h, respectively (P < 0.01). In that study, ovulation was determined every 2 h from 24 to 36 h after treatment, and treatments were administered intramuscularly during mid or early diestrus.…”

“…The preovulatory LH surge occurs approximately 1 to 2 h after treatment with GnRH (Souza et al, 2009;Giordano et al, 2012b;Stevenson and Pulley, 2016;Liu et al, 2019), after which LH concentrations return to basal levels within 5 to 6 h after treatment (Giordano et al, 2012b;Stevenson and Pulley, 2016;Lui et al, 2019). In those studies, GnRH (gonadorelin) doses ranged from 50 to 200 µg, and the peak LH concentration was dependent on the GnRH dose as well as P4 concentrations at the time of treatment.…”

Graduate Student Literature Review: Effects of human chorionic gonadotropin on follicular and luteal dynamics and fertility in cattle

“…Time from treatment to ovulation may vary among GnRH (gonadorelin) and hCG, depending on the estrous cycle phase when the treatment is administered (Liu et al, 2019;Cabrera et al, 2021b). However, regardless of the estrous cycle phase, cows treated with hCG ovulate later than cows treated with GnRH (gonadorelin; Liu et al, 2019).…”

“…Time from treatment to ovulation may vary among GnRH (gonadorelin) and hCG, depending on the estrous cycle phase when the treatment is administered (Liu et al, 2019;Cabrera et al, 2021b). However, regardless of the estrous cycle phase, cows treated with hCG ovulate later than cows treated with GnRH (gonadorelin; Liu et al, 2019). In both studies, the difference in time for ovulation between hCG and GnRH is between 2 and 5 h. It was speculated that the ovulation might occur later after hCG treatment than GnRH because of the delayed time to hCG or LH peak concentration, which is reached 4 h after treatment with hCG (Nascimento et al, 2013) versus 1 to 2 h after treatment with 4 different GnRH analogs (Souza et al, 2009;Giordano et al, 2012).…”