Effect of eCG on the follicular dynamics and vascularization of crossbred cows with different circulating progesterone concentrations during synchronization of ovulation in an FTAI protocol

Abstract

This study aimed to evaluate the effect of treatment with equine chorionic gonadotrophin (eCG) on the follicular dynamics and function of crossbred cows with different circulating progesterone (P4) concentrations during synchronization of ovulation in a fixed-time artificial insemination (FTAI) protocol. To this end, 30 crossbred cows were submitted to a pre-synchronization protocol to ensure that all of them presented corpus luteum (CL) at the beginning of the protocol, and were evaluated by transrectal ultrasonography (TRUS) to verify the presence of CL. After that, the animals underwent an ovulation synchronization protocol and evaluation of follicular dynamics and vascularization by B-mode and power-Doppler ultrasound (US). High plasma P4 concentrations at the time of ovulation synchronization negatively influenced follicle diameter on day 10 (D10), preovulatory follicle diameter, and preovulatory follicle wall vascularization area (p<0.05). Cows with high P4 concentration at the time of ovulation synchronization that were treated with eCG showed follicle diameter on D10 and preovulatory follicle diameter and wall vascularization area (p>0.05) similar to those of animals with low P4 concentration at the time of ovulation synchronization. Therefore, high P4 concentrations at the time of ovulation synchronization negatively influence follicular diameter and vascularization, and eCG can be used as a strategy to favor better follicular and luteal response in crossbred cows with high P4 concentrations submitted to an FTAI protocol.

Recombinant bovine somatotropin in the synchronization of ovulation in crossbred dairy cows (Bos taurus indicus × Bos taurus taurus)

“…Studies indicate that the administration of eCG in the protocol increases follicular growth rate since it improves the ovarian follicular development due to follicle-stimulating hormone and luteinizing hormone-like activity [21]. In this context, the present study suggests that all treatments were affected by eCG since the follicular growth rate observed is similar to those reported by other authors, who observed rates ranging from 1.3 to 1.8 mm/day in B. t. taurus using ovulation synchronization protocols [22,23]. Growth rates ranging from 0.7 to 1.8 mm/day in crossbred cows have also been found by other authors [24].…”

Influence of nutritional and ovarian parameters on pregnancy rates of Nelore cows artificially inseminated at fixed time

“…In this context, the FTAI protocols are very useful, and are frequently performed in acyclic cows during the postpartum period, a condition in which the cow has a low LH support and reduced follicular development (Meneghetti et al, 2009;Roche, Crowe, & Boland, 1992). Thus, the administration of Equine Chorionic Gonadotropin (eCG) is an alternative that can be used in hormonal protocols, as it has an activity similar to FSH and LH in ruminants, promoting follicular growth and oocyte maturation (Ferraz et al, 2019;Thedy et al, 2018). In the present study, the 350 IU eCG administration at the moment of the P4 device removal, may have positively influenced the cows' pregnancy rates.…”

Effect of follicular growth promoters on timed artificial insemination in dairy cows.

“…Con la retirada del dispositivo de progesterona intravaginal en los protocolos IATF, es posible inducir un aumento en las frecuencias de los pulsos de la hormona luteinizante (LH) suficiente para el crecimiento final de los folículos dominantes, para estimular el comportamiento del estro y la ovulación (14), un factor que puede explicar por qué los resultados de las tasas de embarazo no difieren entre los tratamientos en el presente estudio.…”