Age and Hormonal Dependence of Acquisition of Oocyte Competence for Embryogenesis in Prepubertal Calves1

Abstract

This research was designed to improve our understanding of oocyte maturation and acquisition of developmental competence of oocytes using prepubertal heifers as a model. Oocytes were collected by ultrasound-guided transvaginal oocyte retrieval from 20 age-matched calves at 5, 7, 9, and 11 mo of age that had or had not received gonadotropin stimulation. Numbers of oocytes recovered from unstimulated heifers decreased with age, being 15 +/- 2, 12 +/- 1, 7 +/- 1, and 7 +/- 1 (for 5-, 7-, 9-, and 11-mo-old calves, respectively). Corresponding numbers for the gonadotropin-stimulated heifers were 18 +/- 2, 16 +/- 2, 13 +/- 1, and 15 +/- 2. Cumulus-oocyte complexes were graded from A to D on the basis of their morphology, and the better-grade A and B oocytes were used for in vitro maturation and fertilization. A higher proportion of grade A and B oocytes was found for the stimulated vs. unstimulated prepubertal calves at 5 mo of age (92% vs. 49%, p < 0.05) and 7 mo of age (96% vs. 63%, p < 0.05), but the improvement of this parameter by stimulation was not significant for peri- and postpubertal calves at 9 (53% vs. 38%, p > 0.05) and 11 (53% vs. 38%, p > 0.05) mo of age. Embryo development to morula and blastocyst stages was poorer (0-11%, p < 0.05) for oocytes collected from unstimulated calves at 5-9 mo of age than for those from the age-matched but gonadotropin-stimulated groups (10%, 39%, and 31%, at 5, 7, and 9 mo of age, respectively). In calves 11 mo of age, embryo development to morula and blastocyst stages was similar with and without gonadotropin stimulation (48% vs. 40%, p > 0.05) and was comparable to that of adult cow oocytes (45%, p > 0.05). The data suggest that the acquisition of oocyte competence for normal embryo development in prepubertal calves is influenced by animal age and hormonal treatment.

Estimulação hormonal, punção folicular transvaginal e avaliação ovocitária em bezerras pré-púberes da raça Nelore (Bos taurus indicus)

“…Entretanto, os ovócitos coletados de bezerras são menos competentes para se desenvolver em embriões que os de vacas (Seidel et al, 1971;Palma et al, 1993;Lévesque & Sirard, 1994;Revel et al, 1995;Damiani et al, 1995Damiani et al, , 1996Khatir et al, 1996;Kuwer et al, 1999); esta competência parece aumentar com a idade da bezerra (Presicce et al, 1997), embora Armstrong et al (1992, Irvine et al (1993) e Earl et al (1998 tenham obtido resultados semelhantes para animais pré-púberes e adultos.…”

“…Para aumentar o número de ovócitos viáveis por coleta, o desenvolvimento folicular tem sido estimulado usando-se hormônios gonadotróficos, aplicados em diferentes esquemas, dosagens e produtos, com resultados variáveis e pouco conclusivos (Kajihara et al, 1991;Stubbings et al, 1992Stubbings et al, , 1993Armstrong et al, 1992Armstrong et al, , 1994Revel et al, 1995;Looney et al, 1995;Damiani et al, 1996;Tervit et al, 1997;Presicce et al, 1997;Fry et al, 1998;Malard, 2000;Taneja et al, 2000). Já outros estudos têm optado por coletas mais freqüentes sem a estimulação hormonal (Rick et al, 1996;Presicce et al, 1997;Brogliatti et al, 1999;Majerus et al, 1999).…”

Follicular size affects the meiotic competence of in vitro matured prepubertal and adult oocytes in sheep

“…Moreover, the meiotic competence in bovine species is closely related to the follicular dimension; oocytes derived from small follicles showed a lower capacity to resume meiosis and to develop up to early embryonic stages [4]. Previous works [8,19,23] [9,26,27]. This can be related to defective conditions of oocyte maturation and can also be due to the reduced size of oocytes and follicular population [17] and a small size of volume fractions of mitochondria and cortical granules [25].…”

In vitro developmental competence of prepubertal goat oocytes cultured with recombinant activin-A

“…In general, prepubertal oocytes show reduced developmental competence, when compared with results obtained with adult oocytes (Armstrong, 2001). Indeed, the defective capacity of these oocytes to develop up to blastocyst at a rate equivalent to that of adult oocytes has been reported by several other studies in cattle (Presicce et al, 1997), in sheep (Ledda et al, 1997), in pig (Marchal et al, 2001) and more recently in goats stimulated hormonally (Leoni et al, 2009).…”