**4.5.2 GnRH (gonadotrophin-releasing hormone)**

The administration of GnRH around the insemination time aims to accelerate and ensure ovulation in cows, acting directly on the pituitary, stimulating the secretion and release of gonadotrophins, such as LH and FSH, and promoting the preovulatory LH peak, which is essential for follicular dehiscence. In many cases, RBC syndrome is associated with ovulatory defects, as anovulation, delayed ovulation or gonadotrophin release failure.

If luteal deficiency is suspected as reproductive failure in cows, GnRH (100 µg) could be used on day 5 post-AI (Gonzalez-Stagnaro, 1993). GnRH induces LH and FSH discharge pituitary, promotes increased levels of progesterone and exerts a luteoprotector (luteotrophic), increasing fertility in RBCs associated with subfunctional CL or ovulation defects. The mentioned treatment has also been combined with intrauterine antibiotic (infusion of 30-50 ml containing 300000 IU penicillin and 0,5 g streptomycin), increasing fertility in RBCs. This treatment could be more appropriate when abnormal vulvar conformation is present.

A comprehensive study carried out in RBCs indicates that the administration of GnRH at the AI time may be beneficial for improving fertility in these cows (Stevenson et al., 1990). These authors do not recommend the use of double insemination in RBCs, in contrast with Singh et al. (2005) who suggest that pregnancy rates can be improved by increasing the insemination frequency.
