This study investigates the effect of cortisol levels on immune system homeostasis during the peripartum period. A total of 344 multiparous cows of four different breeds were assessed in Colombia. Venous blood samples were collected after morning milking by coccygeal venipuncture into vacutainer tubes, which was carried out 30 days before calving until 75 days postpartum. A solid-phase radioimmunoassay (RIA) was used to determine levels of T3, T4, cortisol, progesterone, and insulin. Results revealed that hormone levels were within the normal range. A significant variation (p<0,01) in cortisol levels was observed between Bos indicus and Bos taurus cattle breeds. However, they did not vary during different collection periods, so our hypothesis that cortisol significantly affects behavioral homeostasis was not confirmed. We conclude that the physiology of cows in the postpartum period suffers profound endogenous regulation under different management systems; this occurs even under stress conditions in order to achieve homeostasis, regardless of cortisol levels.