Evaluating calcium concentrations in serum of pasture-grazed dairy cows treated with an oral Solanum glaucophyllum calcium bolus within 12 h postpartum

Oral calcium boluses can increase serum calcium after calving, but effects may be short-lived, so repeat dosing is often needed during the highest-risk period for hypocalcaemia. Adding vitamin D glycosides may help sustain the post-treatment rise in calcium. The primary objective was to compare serum calcium, magnesium, and phosphorus concentrations in dairy cows treated with either 1) a new bolus containing calcium salts and vitamin D3 glycosides from Solanum glaucophyllum , 2) a commercial calcium bolus without vitamin D3 glycosides, or 3) no treatment. Methods During the spring 2024 calving season in New Zealand, we conducted a prospective, randomized, controlled trial in 129 dairy cows from two commercial farms. Within 12 h of calving, cows received either a new formulation (two boluses given simultaneously) containing calcium salts plus vitamin D glycosides ( Solanum glaucophyllum ) (new bolus; n=44), a commercially available calcium-only bolus (two boluses given 12 h apart; n=42), or no treatment (control; n=43). Blood samples were collected at enrolment (0 h) and repeatedly to 72 h post-enrolment to measure serum total calcium, magnesium, and phosphorus concentrations. Associations between treatment and serum mineral concentrations were assessed using mixed linear regression models adjusted for farm, cow age, and sampling time, with an autoregressive structure to account for repeated measures. Results Compared with controls, the new bolus increased serum total calcium by up to 0.33 mmol/L from 2 to 72 h post-treatment. Compared with the calcium-only bolus, the new bolus maintained higher serum total calcium across the post-treatment period by up to 0.37 mmol/L, although data at 6, 12, and 14 h were compatible with little to no difference between treatments. The new bolus also increased serum phosphorus from 24 to 72 h compared with both other groups, with the 24 h comparison against controls compatible with no difference. Both bolus treatments reduced serum magnesium compared with controls by up to 0.23 mmol/L (new bolus) and 0.13 mmol/L (calcium-only), with greater and more prolonged reductions for the new bolus. Conclusion A calcium bolus containing vitamin D glycosides sustained higher serum total calcium for up to 72 h after treatment in pasture-based dairy cows, supporting its potential to reduce hypocalcaemia risk.