Background: Cows have an increased need for energy after calving due to milk production for nursing calves and the recovery of reproductive performance. Blood metabolites are associated with the reproductive ability of primiparous Hanwoo cows, but the relationship between changes in blood metabolite concentrations and reproductive ability remains unclear. The present study investigated the relationship between changes in blood metabolites from 2 to 5 weeks after calving and the recovery of reproductive ability in primiparous Hanwoo cows. Methods: Blood samples were obtained from 26 primiparous Hanwoo cows of average body condition score 3.0 (range, 1-5) weekly from 2 to 7 weeks postpartum and at the time of estrus, and the concentrations of blood metabolites were measured. Changes in blood metabolite concentrations were found to be associated with the recovery of reproductive function after calving. Results: The concentrations of non-esterified fatty acids (NEFA) and blood urea nitrogen (BUN) 3 to 4 weeks after calving were significantly associated with the first days of ovulation. Ovulation resumed when the average NEFA concentration reached 199.0 μEq/L, and the first normal estrus cycle was established when the average total cholesterol (T-Chol) concentration reached 169.1 mg/dL. Conclusions: Metabolic status 3 to 4 weeks postpartum influenced the resumption of estrus and ovulation in primiparous Hanwoo cows. Furthermore, increased T-Chol concentration was associated with the initiation of a normal estrus cycle.

ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
    Animals, feed management, and experimental design
    Collection of blood and biochemical analysis of bloodmetabolites
    Evaluation of reproductive ability and fertility
    Statistical analysis
RESULTS
DISCUSSION
CONCLUSION
REFERENCES

• Hyoun-Ju Kim(Planning and Coordination Division, National Institute of Animal Science, Rural Development Administration, Wanju 55315, Korea)
• Yonghwan Kim(Hanwoo Research Center, National Institute of Animal Science, Rural Development Administration, Pyeongchang 25340, Korea, Department of Animal Resources Science, Kongju National University, Yesan 32439, Korea)
• Shil Jin(Hanwoo Research Center, National Institute of Animal Science, Rural Development Administration, Pyeongchang 25340, Korea)
• Jeong-Il Won(Hanwoo Research Center, National Institute of Animal Science, Rural Development Administration, Pyeongchang 25340, Korea)
• Sung-Sik Kang(Hanwoo Research Center, National Institute of Animal Science, Rural Development Administration, Pyeongchang 25340, Korea) Corresponding author
• Bongki Kim(Department of Animal Resources Science, Kongju National University, Yesan 32439, Korea)