Desenvolvimento folicular no pós-parto de vacas da raça Gir tratadas com acetato de buserelina (GnRH) ou gonadotrofina coriônica humana (hCG) Follicular development in Gir breed cows (Bos indicus) treated with buserelin acetate or human chorionic gonadotrophin during the postpartum period

Foram utilizadas 22 vacas da raça Gir (Bos indicus) em anestro pós-parto, amamentando e mantidas sob regime de pastejo. O padrão de crescimento folicular foi estudado em 15 animais, enquanto os outros sete foram utilizados somente no acompanhamento da resposta aos tratamentos hormonais. Ultra-sonografia em tempo real foi realizada diariamente, do quarto ao qüinquagésimo dia de lactação, por meio de aparelho equipado com probe de 5MHz. Nenhum animal apresentou estro, ovulação ou luteinização folicular durante o período de avaliação. Verificaram-se quatro a oito ondas foliculares surgindo em intervalos de seis a sete dias, cujo diâmetro máximo dos folículos dominantes e subordinados foi de 8,9±0,6 e 6,3±0,7mm, respectivamente. Aos 56 dias pós-parto, as 22 vacas foram divididas em dois grupos: 11 tratadas com 4,2 mig de acetato de buserelina e 11 com 3.000UI de hCG. A ovulação, regressão e luteinização folicular foram verificadas em animais dos dois tratamentos e uma nova onda folicular surgiu dentro de dois a três dias após a terapia hormonal. Corpos lúteos de menor tamanho e concentrações de progesterona abaixo de 1ng/mL indicaram baixa atividade luteal.<br>This experiment was carried out with 22 anestrus Gir cows (Bos indicus), with the postpartum follicular growth studied in 15 of these suckling and kept on pasture, while the seven others were used only for hormonal treatments. Daily real time ultrasonography was done from 4th to the 50th day, using B-mode ultrasound scanner equipped with a linear array 5.0MHz probe. No animal showed estrus, ovulation or follicular luteinization during de experimental period. Four to eight follicular waves emerged each six or seven days and maximum diameter of dominant and subordinate follicles were 8.9±0.6mm and 6.3±0.7mm, respectively. On day 56 of postpartum all cows were separated in two groups: 11 cows were treated either with 4.2 mug of buserelin acetate and 11 with 3,000UI of hCG. Ovulation, follicular regression and luteinization were observed in the two treatments animals, and one new follicular wave emerged within two to three days after the hormonal treatments. Small size corpus luteum and progesterone concentrations under 1ng/mL showed lower luteal activity

Follicle environment and quality of in vitro matured oocytes

In mammalian reproduction, the oocyte depends on the ovarian follicle for most of its growth. They form a bipolar partnership and the status of one will impact the functioning of the other. When oocytes are removed from their follicle by ovulation, they have normally completed all the steps required to begin their journey into the oviduct and drive the early embryonic development. When oocytes are removed from their follicle before natural ovulation, the process by which they acquire all the important components for their journey might not be completed and their ability to mature, fertilize or develop into embryos or to term might be compromised. Animal models have been useful to define the important steps required for the oocyte’s growth phase, and in the mouse, when the oocyte has reached its full size, the program is ready. This is not the case in larger mammals where the completion of growth does not ensure that the oocyte is fully capable of undergoing all the steps to the embryo and to term. The final steps of oocyte preparation also involve a progressive condensation of the chromatin that may facilitate normal maturation but may also indirectly reduce the lifespan of the oocyte. In such a scenario, the oocyte would have an expiration date when fully competent. In humans, a number of indications may justify the aspiration of oocytes from unstimulated patients and the development of an in vitro maturation (IVM) process that would allow fertilization and subsequent development. This objective could be realized by a better understanding of the essential follicular contribution required before removing the oocyte. Therefore, this review will focus on the large animal models where IVM has been used and studied for more than 25 years. The status of the follicle at the time of oocyte recovery and the status of the oocyte’s chromatin will be described in detail as they have a significant impact on the outcome