The effects of calcium supplementation of dairy cattle after calving on milk, milk fat and protein production, and fertility

Aim. To determine the effect of calcium supplementation of dairy cattle aft er calving on serum concentrations of calcium, magnesium, and phosphorous a fter calving, and on reproductive and productive performance in the followi ng lactation. Methods. This was a double-blind randomised clinical trial using 356 dairy cows of parity 3 or greater from six seasonally calving commercial dairy he rds. Cows were randomly assigned to a treatment and control group. The trea tment group received two doses of 380 ml of calcium chloride in oil (49 g o f elemental calcium); the first dose was given as soon as practical after c alving and the second 12 hours later. Control cows received 380 mi of a pla cebo using the same treatment regime. Treatment and control cows had blood samples taken during the first 7 days after calving to determine serum calc ium, magnesium and phosphorous levels. Treatment and control cows were moni tored throughout the lactation to measure production and reproductive perfo rmance. Results. Treatment had no effect on PSM to first service intervals. Treatme nt significantly reduced PSM to conception intervals in only one of the fou r herds with data available for analysis (p = 0.09). There was no differenc e between treatment groups for adjusted corrected milk yield calculated fro m the first herd test milk yield (p = 0.93) or 305-day milk solids producti on (p = 0.19). Conclusion. Further studies are required to identify reasons for the betwee n-herd effectiveness of calcium chloride treatment in improving fertility.