Abstract
Background: Hypocalcemia is one of the most common transition period disorders that affects dairy cows and has been divided into clinical and subclinical types.
Aim: This study aimed to investigate the relationship between postpartum serum calcium (Ca) concentrations with metabolic disorders and body condition score (BCS) in Holstein dairy cows.
Methods: Two hundred and seventy-one Holstein cows were blocked from two commercial dairy herds based on parity (primiparous and multiparous) and serum Ca concentrations on calving day, 1 and 2 days postpartum were allocated to 1 of 3 groups: 1) Serum Ca concentration >8.5 mg/dL at the calving day, 1 and 2 days postpartum (normocalcemic); 2) serum Ca concentration ≤8.5 mg/dL on the calving day and 1 or 2 day postpartum (TSCH; transient subclinical hypocalcemia); and 3) serum Ca concentration ≤8.5 mg/dL on the calving day, 1 and 2 days postpartum (PSCH; persistent subclinical hypocalcemia).
Results: The results showed that the primiparous and multiparous cows had the highest TSCH and PSCH percentages, respectively. Ca status after calving did not affect the BCS changes, incidence of milk fever, hypomagnesemia and hyperketonemia, and clinical and subclinical endometritis. The incidence of retained placenta, metritis, and subclinical mastitis were affected by Ca status after calving, so PSCH cows experienced 6.28, 6.43, and 5.9 times more retained placenta, metritis and subclinical mastitis than normocalcemic cows, respectively. The culling rate within the first 60 days in milk (DIM) for PSCH cows was 4.61 times more than for normocalcemic cows.
Conclusion: Overall, the results of the study showed that cows with PSCH had a higher incidence of retained placenta; uterine infections, subclinical mastitis and culling rate, but cows with TSCH were similar to healthy cows in terms of metabolic disorders and culling rate.

Key words: Transient subclinical hypocalcemia, Persistent subclinical hypocalcemia, Mastitis, Retained placenta, Metritis