title: The effects of calcium supplementation of dairy cattle after calving on milk, milk fat and protein production, and fertility.
abstract: OBJECTIVE
  To determine the effect of calcium supplementation of dairy cattle after calving on serum concentrations of calcium, magnesium, and phosphorous after calving, and on reproductive and productive performance in the following 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 herds. Cows were randomly assigned to a treatment and control group. The treatment group received two doses of 380 ml of calcium chloride in oil (49 g of elemental calcium); the first dose was given as soon as practical after calving and the second 12 hours later. Control cows received 380 ml of a placebo using the same treatment regime. Treatment and control cows had blood samples taken during the first 7 days after calving to determine serum calcium, magnesium and phosphorous levels. Treatment and control cows were monitored throughout the lactation to measure production and reproductive performance.
  
  
  RESULTS
  Treatment had no effect on PSM to first service intervals. Treatment significantly reduced PSM to conception intervals in only one of the four herds with data available for analysis (p = 0.09). There was no difference between treatment groups for adjusted corrected milk yield calculated from the first herd test milk yield (p = 0.93) or 305-day milk solids production (p = 0.19).
  
  
  CONCLUSIONS
  Further studies are required to identify reasons for the between-herd effectiveness of calcium chloride treatment in improving fertility.
authors: Institute of Veterinary Animal and Biomedical Sciences, Massey University, Private Bag 11222, Palmerston North, New Zealand.
authors: M A
authors: MA
authors: Stevenson
authors: N B
authors: NB
authors: Williamson
authors: D W
authors: DW
authors: Hanlon