**4.5.3 Exogenous gonadotrophin**

These hormones have been used in RBCs to induce ovulation and exert the luteotrophic effect on the CL.

In 1965, Roussel et al. administered intramuscularly pregnant mare serum (PMS) on day 15 or 16 of the estrous cycle, obtaining a conception rate of 73,9% in RBCs compared with 44,4% of control cows.

However, HCG is the most used exogenous gonadotrophin for treating RBC syndrome.

Treatment with hCG on day 5 after insemination can achieve higher levels of progesterone for at least 2 weeks, due to the development of accessory CL (Walton et al., 1990)
