Objectives were to determine effects of an injectable formulation of calcitriol on Ca concentration, risk of subclinical hypocalcemia, and health in dairy cows. Cows were blocked by lactation number (1 vs. ≥2) and calving sequence, and within each block, randomly assigned to receive, within 6 h of calving, subcutaneously vehicle only (Control, n = 450), 200 μg of calcitriol (Cal200, n = 450), or 300 μg (Cal300, n = 450). Blood samples were collected before treatment administration, and on d 1, 2, 3, and 5. Samples were analyzed for blood ionized Ca, and total plasma Ca and Mg. Vaginal discharge (VD) was evaluated at 4, 6, and 8 DIM, and cows with VD reddish/brownish foul smell were diagnosed with metritis. Morbidity was evaluated until 60 DIM, and responses measured included metritis, mastitis, displaced abomasum, digestive and respiratory disorders. At 35 DIM, VD was scored for diagnosis of purulent vaginal discharge (PVD, VD > 2, mucopurulent discharge). Cyclicity was evaluated by presence of a corpus luteum (>20mm) in at least one of 2 ovarian ultrasound scans performed at 35 and 49 DIM. Data were analyzed using PROC MIXED and PROC GLIMMIX of SAS. Cows receiving calcitriol resulted in greater concentration of blood ionized Ca and plasma total Ca during the first 5 and 3 DIM, respectively, whereas concentration of plasma Mg were reduced during the first 3 DIM (Table). Treatment with calcitriol did not affect the incidence of metritis, puerperal metritis, morbidity by 60 DIM, PVD, and cyclicity (Table 1). Calcitriol treatment was effective to improve Ca concentrations during the first 3 DIM, but was unable to improve health performance. Table 1.

Parameter	Treatment			SEM	P-value
	Control	Cal200	Cal300
Ionized Ca, mM	1.12	1.22	1.27	0.02	<0.01
Total Ca, mM	2.31	2.65	2.70	0.03	<0.01
Total Mg, mM	0.65	0.54	0.52	0.02	<0.01
Metritis, %	37.5	38.1	34.1	3.0	0.51
Puerperal metritis, %	9.9	8.3	9.6	1.5	0.78
Morbidity by 60 DIM, %	60.2	62.6	63.4	2.9	0.60
Purulent vaginal discharge, %	26.7	32.8	30.2	2.5	0.23
Cyclicity, %	68.3	74.7	73.5	2.9	0.15