Effects of GnRH and hCG administration during early luteal phase on estrous cycle length, expression of estrus and fertility in lactating dairy cows

Accessory corpus luteum induced by human chorionic gonadotropin on day 7 or days 7 and 13 of the estrous cycle affected follicular and luteal dynamics and luteolysis in lactating Holstein cows

“…These results also agree with a recent study from our laboratory that determined that a single hCG treatment from d 5 to 7 of the estrous cycle decreased the proportion of lactating multiparous Holstein cows returning in estrus until d 32 of the cycle (Cunha et al, 2021). In addition, cows returning to estrus after treatment had a prolonged estrous cycle (Cunha et al, 2021). Thus, the effects of hCG on the estrous cycle dynamics must be considered in farms that use detection of estrus as a rebreeding strategy and use hCG post-AI or before ET to improve fertility (Nascimento et al, 2013;Niles et al, 2019).…”

“…Moreover, the majority of them were in hCG treatments (17/20), suggesting that induction of accessory CL with hCG during diestrus may disrupt luteolysis and ovulation. These results also agree with a recent study from our laboratory that determined that a single hCG treatment from d 5 to 7 of the estrous cycle decreased the proportion of lactating multiparous Holstein cows returning in estrus until d 32 of the cycle (Cunha et al, 2021). In addition, cows returning to estrus after treatment had a prolonged estrous cycle (Cunha et al, 2021).…”

“…On the contrary, a recent study from our laboratory indicated that a single administration of 3,300 IU of hCG from d 5 to 7 of the estrous cycle increased the estrous cycle length in noninseminated lactating Holstein and Jersey cows (Cunha et al, 2021). Moreover, hCG decreased the proportion of multiparous cows returning to estrus (Cunha et al, 2021), indicating that accessory CL induced by hCG may affect luteal and luteolytic dynamics. The study did not collect ovarian and hormone data throughout the estrous cycle; therefore, it is still unclear how hCG prolonged the length of the estrous cycle.…”

“…(1-5) (10-30) Interval between first onset of functional luteolysis and ovulation, d ± SEM (range) 6.9 ± 0.3 a 21.6 ± 2.8 b 20.2 ± 1.8 b <0.001 (4-13) (9-33) (14-26) Interval between P4 <1.00 ng/mL and ovulation, d ± SEM 4.4 ± 0.2 a 18.8 ± 2.9 b 3.9 ± 0.5 a <0.001 Interval between P4 ≤0.50 ng/mL and ovulation, d ± SEM 4.0 ± 0.2 a 18.4 ± 2.9 b 3.4 ± 0. cows determined that a single administration of 3,300 IU of hCG from d 5 to 7 of the estrous cycle reduced the proportion of multiparous cows returning to estrous and prolonged the estrous cycle (Cunha et al, 2021). In farms that use detection of estrus to rebreed cows and heifers post-AI, the use of hCG post-AI could affect their reproductive performance.…”

Effect of nerve growth factor-β administered at insemination for lactating Holstein dairy cows bred after timed-artificial insemination protocol

“…Strategies aimed at improving endogenous progesterone production or administration of luteotropic agents have been proposed to be beneficial. A commonly described mechanism for increasing peripheral progesterone concentrations is administering human chorionic gonadotropin (hCG; Wiltbank et al, 2011;Rizos et al, 2012;Cunha et al, 2021Cunha et al, , 2022. This LH-like hormone induces ovulation of the first-wave dominant follicle to form accessory CL, producing additional progesterone.…”