Use of 1,25(OH)2 vitamin D3 to maintain postpartum blood calcium and improve immune function in dairy cows

Abstract Text:

Objectives were to determine the effects of a slow-release injectable formulation of 1,25-dihydroxyvitamin D₃ (calcitriol) on mineral metabolism and measures of immune function in recently calved Holstein cows. Cows were blocked by parity (2 vs. >2) and calving sequence and, within each block, randomly assigned to receive subcutaneously 300 μg of calcitriol (DHVD, n=25) or vehicle (CON, n=25) within 6 h of calving. Blood and urine were sampled before treatment application, 12 h later, and on d 1, 2, 3, 5, 7, 9, 12, and 15 postpartum. Samples were analyzed for total (tCa) and ionized Ca (iCa), magnesium (Mg), phosphorus (P), calcitriol, nonesterified fatty acids (NEFA), beta hydroxybutyrate (BHBA), glucose, serotonin (5-HT) and crosslaps (CTX-1). Neutrophil function was evaluated in the first week postpartum. Intake of DM and production performance were evaluated for the first 42 d postpartum. Data were analyzed by ANOVA with mixed models using the MIXED procedure of SAS. DHVD increased (P<0.01) concentrations of calcitriol within 4 h of application from 24 to 420 pg/mL, which returned to baseline within 3 d. Blood iCa and tCa took 12 and 24 h, respectively, to increase after treatment with VitD compared with CON. Concentrations of iCa (CON=1.05 vs. DHVD=1.18 mM), tCa (CON=2.11 vs. DHVD=2.35 mM), and P (CON=1.51 vs. DHVD=2.06 mM) remained elevated (P<0.01) in DHVD until 3, 5 and 7 d postpartum, respectively. Concentration of Mg (CON=0.76 vs. DHVD=0.67 mM) was less (P<0.01) in DHVD cows until 5 d postpartum. DHVD cows excreted more urinary Ca (CON=0.6 vs. DHVD=1.7 g/d; P<0.01) and Mg (CON=3.6 vs. DHVD=5.5 g/d; P=0.02) in the first 5 and 1 d postpartum, respectively. Concentrations of glucose, NEFA, BHBA, 5-HT and CTX-1 in plasma did not differ between treatments. DHVD improved neutrophil function compared with CON. Relative to a reference cow, the percentage of neutrophils with oxidative burst activity (CON=80.0 vs. DHVD=101.0%; P=0.03), the mean fluorescence intensity (MFI) for oxidative burst (CON=96.0 vs. DHVD=105.0%; P=0.09), and the MFI for phagocytosis (CON=94.0 vs. DHVD=110.0%; P=0.03) were all greater for DHVD than CON cows. Intake of DM and yields of milk and milk components did not differ between treatments. Administration of 300 μg of calcitriol at calving was safe and effective in increasing plasma concentrations of calcitriol, iCa, tCa, and P for the first few days after treatment, and improved measures of innate immune function in early lactation Holstein cows.

Keywords: calcitriol, hypocalcemia, transition period