Effects of cortisol levels on reproductive success in cattle of different temperaments during fixed-time artificial insemination (FTAI)

Abstract

The present study was designed to assess the effect of stress on the reproductive performance of cattle. For this purpose, a total of 137 cows were divided into two groups: 65 belonging to the Azores Lydia breed and 72 crossing Aberdeen-Angus with Limousine, free of IBR, Chlamydia and BVD diseases and with a body condition score ranging from 2.75 to 4.0. Eight days before starting the experimental procedures, animals passed through the containment sleeve every other day for routine and human presence. For the synchronization protocol, a progesterone-impregnated controlled internal drug release (CIDR®) insert was placed intravaginally, and an injection of GnRH was given. After 7 days, PGF2α was administered, and the CIDR® was removed. Sixty hours after removal, cows were inseminated once after another injection of GnRH to induce ovulation, and pregnancy diagnosis was performed by ultrasonography 30 days after artificial insemination. Peripheral blood was collected in 5 ml tubes with a Z Serum Sep Clot Activator, and cortisol was measured using the IMMULITE 2000 Immunoassay System ®. Our results indicated significant differences (p≤0.05) in the cortisol levels among both groups (beef crossbred cows vs Azores Lydia) of 4.3±0.3 ng/dl and 5.8±0.4 ng/dl, respectively. The pregnancy results were also significantly different: 63.7% vs 45.6%, respectively, for beef crossbred and "Azores Lydia" cows. The present study clearly demonstrated a negative correlation between cortisol levels and pregnancy rates after fixed-time artificial insemination. The low levels of cortisol observed in the animals and particularly in the Azores Lydia breed, when compared to other studies carried out on these animals, must be due to the passage of the animals in the sleeve, allowing them to habituate to a routine, as well as to human presence.