In vitro fertilization: alternative for genetic improvement in cattle
Abstract
The great expectations created by in vivo embryo production procedures have been disappointed over time. This is a consequence of the fact that its yield is not as high as it was originally supposed, because the number of transferable embryos obtained in each wash is low, stabilizing around 4.8 the bovine species; the existence of females that do not respond to treatments to induce multiple ovulation; the need to respect rest periods between two consecutive collections and the obligation that donors be in perfect gynecological conditions, a situation difficult to maintain in multiparous females. These circumstances have created the need to develop an alternative procedure for the production of embryos. This procedure is based on the use of immature oocytes, collected directly from the ovary regardless of the age and physiological situation of the female. This technique offers the possibility of turning the female into a gamete producer, equating her to the male semen producers for artificial insemination, which would have numerous advantages in the selection programs. However, there are several physiological differences between males and females that make it difficult to achieve this goal. Thus, the oocyte population present in the ovary is limited and does not renew itself, but decreases progressively with age as a consequence of atresia. In addition, the oocytes are not released to the outside, being necessary to extract them from the oviduct or the ovarian cortex. On the other hand, the oocyte population is very heterogeneous in terms of quality and degree of maturity.