الكاتب: Multiple References

The Brazilian sheep flock consists of 15 million animals, with approximately 58% raised in the northeastern region (IBGE, 2004). Sheep reared in this area represent an important economic source for breeders, where they are used mainly for meat and skin production. However, production efficiency of most local animals from northeastern Brazil is low, owing to management conditions but especially because of the low genetic quality of the flock. Widespread genetic improvement of sheep is dependent on the ability to use reproductive technologies, such as artificial insemination and embryo transfer. There are major limitations in the application of reproductive technologies in sheep, due to the inability to relax or dilate the cervix. Anatomically, the cervix of sheep is a rigid, long, tightly closed structure crossed by five to seven offset spiral folds that form crypts, believed to hold ejaculated spermatozoa (More, 1984). The second fold cranial to the vagina generally presents the greatest obstacle to instrument insertion through the sheep cervix (Croy et al., 1999). Relaxation of the cervix would provide the dilatation necessary to facilitate noninvasive artificial insemination. Cervical relaxation would also permit nonsurgical embryo recovery or transfer ‘per vaginum’ (Mylne et al., 1992; McKelvey, 1999).