Abstract
Background:
Repeat breeder cows (RBCs) are characterized by failure to conceive at least 3 times without anatomical or infectious abnormalities. This condition presents a major challenge to farm fertility and profitability.

Aim:
This study aimed to evaluate hematological and serum biochemical profiles at the time of artificial insemination (AI) to identify potential indicators of subfertility and the association with pregnancy rate.

Methods:
A total of 14 RBCs received estrous synchronization protocol comprising 2 doses of 500 µg Cloprostenol at 11-day intervals, followed by AI within 72h after the second injection. Pregnancy was diagnosed 60 days after insemination, and the outcome was analyzed descriptively. Factors affecting pregnancy were analyzed using Fisher’s exact test, while hematological and serum biochemical parameters were compared between pregnant and nonpregnant cows in the next estrous cycle using the t-test.

Results:
These results showed that 7 out of 14 cows (50%) were pregnant. Among the variables assessed, the timing of AI significantly affected pregnancy rates. Analysis of the hematological profile revealed significant differences in the percentage of granulocytes and midcells between pregnant and nonpregnant cows. Furthermore, biochemical profiles showed that the levels of blood urea nitrogen (BUN) andthe BUN/creatinine ratio were considerably higher in nonpregnant cows (P < 0.05).

Conclusion:
This study suggests that physiological conditions during AI affect pregnancy outcomes in RBCs. In addition to management practices, these results provided valuable information regarding the diagnosis of fertility problems in RBCs receiving AI.

Key words: Artificial insemination, Biochemical profile, Estrous synchronization, Hematological profile, Repeat breeding