Does knowledge of blood calcium concentration at 2 DIM impact decisions of calcium supplementation?

Does knowledge of blood calcium at 2 DIM impact decisions of calcium supplementation?

H. A. McCray1*, C. R. Seely2, and J. A. A. McArt2

1 College of Veterinary Medicine, Cornell University, Ithaca, NY 14853
2 Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853

Delaying oral Ca supplementation may benefit cows with low blood Ca at 4 DIM, a time when subclinical hypocalcemia (SCH) is associated with negative health and production outcomes. Our objective was to determine if delayed oral Ca supplementation improves Ca status at 4 DIM and milk production in cows with reduced blood Ca at 2 DIM. Data were collected from a previously conducted randomized controlled trial on multiparous cows (n = 518) from 4 farms in NY. Cows were randomly assigned to 1 of 2 treatment groups at calving: 1) control (CON; no Ca supplementation, n = 259); 2) bolus (BOL; 43g oral Ca administered at 48 and 72 h post-calving, n = 259). We used generalized linear mixed models to identify serum total Ca (tCa) concentrations at 2 DIM that maximized the difference in milk production to diagnose SCH. Cows were classified as normocalcemic (NC; parity 2 tCa > 1.9 mmol/L; parity 3 tCa > 1.87 mmol/L; n = 457) or SCH (parity 2 tCa ≤ 1.9 mmol/L; parity 3 tCa ≤ 1.87 mmol/L; n = 61). Cows were further classified into 1 of 4 SCH-treatment groups (SCHTRT) based on their 2 DIM SCH status and random treatment allocation: 1) NC-CON (n = 165), 2) SCH-CON (n = 29), 3) NC-BOL (n = 165), or 4) SCH-BOL (n = 27). Generalized linear mixed models were used to analyze the difference in tCa at 2 and 4 DIM and milk yield for the first 10 wks of lactation between SCHTRT groups with separate analyses performed for parities 2 and 3. For both parities, cows in SCH-CON and SCH-BOL groups had lower tCa at 2 DIM than cows in NC-CON and NC-BOL groups (P < 0.001). At 4 DIM, tCa concentrations were similar for all SCHTRT groups in parities 2 (P = 0.7) and 3 (P = 0.6). Mean milk yield differed between SCHTRT groups in parity 2 with SCH-CON and SCH-BOL cows producing more milk than NC-CON and NC-BOL cows (P = 0.002). Notably, in parity 3, SCH-BOL cows produced 56.3 (95% CI = 53.1, 59.3) kg, SCH-CON 51.7 (48.6, 54.7) kg, NC-BOL 50.6 (49.0, 52.2) kg, and NC-CON 48.7 (46.9, 50.5) kg (P = 0.001). Our results suggest that while delayed Ca bolus administration does not improve blood Ca status, it does support increased milk production in specific groups of cows.

Keywords: subclinical hypocalcemia, oral bolus