Relationship between serum magnesium concentration during the transition period, peri‑ and postpartum disorders, and reproductive performance in dairy cows

This study evaluated the relationship between serum magnesium concentration, peri‑ and postpartum disorders, and reproductive performance in dairy cows. Blood samples were collected from 198 Holstein cows 4 weeks prepartum, after calving, and 1, 2, 4, 6, and 8 weeks postpartum to measure serum magnesium and/or progesterone concentrations. To determine the relationship between serum magnesium concentration and peri‑ or postpartum disorders, cows were divided into two groups based on their mean serum magnesium concentration 4 weeks prepartum and just after calving: a Low-Mg group (1.45-2.65 mg/dL, n = 110) and a High-Mg group (2.70-5.40 mg/dL, n = 88). Analysis of these groups showed that the incidences of dystocia, retained placenta, endometritis, and lameness were lower (P < 0.05-0.01) in the High-Mg than in the Low-Mg groups. To determine the relationship between serum magnesium concentration during the transition period and reproductive performance, cows were divided into two groups based on their mean serum magnesium concentration from 4 weeks prepartum to 4 weeks postpartum: a Low-Mg group (1.80-2.59 mg/dL, n = 116) and a High-Mg group (2.60-4.17 mg/dL, n = 82). The probability of cyclicity resuming (shown by a progesterone concentration ≥ 1 ng/mL) by 8 weeks postpartum was higher in the High-Mg group (hazard ratio [HR]: 1.70; P < 0.01) than that in the Low-Mg group. Moreover, the probabilities of first insemination by 150 days and pregnancy by 210 days postpartum were higher (HRs: 2.16 and 2.36, respectively; P ≤ 0.0001) in the High-Mg than in the Low-Mg groups, resulting in the mean calving-to-conception interval being 25 days shorter in the High-Mg group. In conclusion, high serum magnesium concentration during the transition period is associated with lower incidences of peri‑ and postpartum disorders and improved reproductive performance in dairy cows.