Periparturient sequence of physiology surrounding dyscalcemia in multiparous Holstein dairy cows: A prospective cohort study

Although most cows effectively normalize their calcium status following the physiological decline in serum total calcium (tCa) that occurs after parturition, a substantial proportion of dairy cows develop dyscalcemia. Dyscalcemia is defined as tCa ≤2.2 mmol/L at 4 DIM and is associated with poor productivity, reduced reproductive success, and increased risk of disease. The physiological relationships underlying these associations are poorly understood; therefore, our objective in this prospective cohort study was to establish the sequence of physiology related to dyscalcemia. We enrolled 45 multiparous Holsteins and followed them from 14 d prepartum through 14 DIM. Daily DMI and rumination times were recorded for the duration of the study period. We collected blood samples at -14, -7, -3, and -1 d relative to parturition, every 8 h from parturition through 96 h postpartum, and again at 120 h, 168 h, 240 h, and 336 h postpartum. Serum samples were analyzed for tCa, haptoglobin, and BHB concentrations. Milk yields were evaluated from every milking through 336 h postpartum, and daily milk yields averaged by week were collected through 10 wk of lactation. Cows were classified as dyscalcemic (DYS; tCa ≤2.2 mmol/L; n = 12) or eucalcemic (EU; tCa >2.2 mmol/L; n = 33) based on tCa at 96 h postpartum. Linear mixed effects models were fit for each physiological measure modeled as a function of dyscalcemia status and its interaction with time, accounting for relevant confounding effects and including the random effect of cow. Although we did not detect differences between DYS and EU cows prepartum for any of our measures, we observed marked differences in temporal patterns of postpartum physiological indicators associated with dyscalcemia. Dyscalcemic cows experienced lower intake starting between 24 h and 48 h postpartum (DYS: mean = 16.3 kg/d, 95% CI = 14.5-18.1 kg/d; EU: mean = 20.6 kg/d, 95% CI = 19.5-21.7 kg/d) and lower rumination times beginning at 40 h (DYS: 25 min/h, 95% CI = 19-31 min/h; EU: 38 min/h, 95% CI = 35-42 min/h), followed by higher haptoglobin concentrations at 64 h (DYS: 0.69 g/L, 95% CI = 0.49-0.98 g/L; EU: 0.39 g/L, 95% CI = 0.32-0.48 g/L), and finally lower tCa concentration at 96 h (DYS: 2.11 mmol/L, 95% CI = 2.02-2.21 mmol/L; EU: 2.36 mmol/L, 95% CI = 2.31-2.43 mmol/L). Milk production was lower for dyscalcemic cows throughout 14 DIM by 1.4 kg (95% CI = 0.6-2.1 kg) on average per milking, and milk production was also lower for dyscalcemic cows through 10 wk in lactation by 4.8 kg/d (95% CI = 2.3-7.4 kg/d) on average. Although our study may have limited generalizability due to its single farm and seasonality setting, we have demonstrated that under controlled conditions, early postpartum maladaptation associated with dyscalcemia is first apparent through depressed feed intake and rumination shortly after calving. This sequence of physiology may be relevant to inform the development of interventions.