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How to calculate the correct amount of medication to add to water when using a flow dispenser

We should know the solubility of the main ingredients used that depend on intrinsic factors of the product and the water quality (harness, pH, temperature, contamination, etc...)

Thursday 10 November 2011 (7 years 4 months 10 days ago)

How does a liquid doser work?

Liquid dosers use water pressure as a propelling force. The water activates the piston that sucks the concentrated product out of a container, it dispenses it to the percentage or proportion desired, it homogenizes it with the water in the liquid doser mixing chamber and the solution is sent to exit the apparatus independent of variations in pressure and flow.

Liquid doser

What do you need to know?

Before medicating the water we should know whether the product we are using is soluble (see the previous article: The effect of pH on medications and possible corrections). The stock solution container with homogenizer (mixer) will prevent the production of precipitation, assuring the correct dose.

We should know the solubility of the main ingredients used that depend on intrinsic factors of the product and the water quality (harness, pH, temperature, contamination, etc...)

In order to correctly medicate the water we need to know:

  • The dose of product per kg of live weight (coming up with the quantity per day).
  • The daily water consumption of the animals to be medicated.
  • Final concentration of the product in the drinking water.
  • Dispensing percentage of the stock solution (percentages lower than 2-4% can produce errors).
  • Quantity of stock solution needed.
  • Amount of product to add to the stock solution tank.

Commercial powdered product


By way of example we are going to see how to calculate the different concentrations and quantities.

Let’s imagine that we want to treat 400 20 kg piglets with a 20 mg dose of active product/kg of live weight.

The first step would be to calculate the quantity of active product needed per day, and for that we should:

  • Know the concentration of the commercial product, for example: 10% (10 g of active product per 100 g of commercial product).
  • Calculate the total weight of the animals to be treated: 400 20 kg piglets = 8.000 kg.
  • Determine main ingredient needs: 8.000 kg x 20 mg = 160.000 mg (160 g)
  • Determine the amount of commercial product to use: if for every 100 g of product we have 10 g of active ingredient (10%), then for 160 g we need 160 g x 100 / 10 = 1.600 g of commercial product.

The second step will be to calculate how much water the animals will drink per day, therefore we need to know, or estimate, the animals’ daily consumption:

  • If each piglet drinks 2 liters/day, 400 piglets drink 800 liters/day.

The third step will be to determine the correct gauge or position of the dispenser regulator: 2:100 (2%), 5:100 (5%). This percentage does not refer to the final dose of product in the drinking water (a common error), but rather to the incorporation of the stock solution in the drinking water.

  • If with the position of the regulator chosen, the number of “clicks” that we hear in 15 seconds is over 25 (the “click” is the sound the piston makes when it hits the top and bottom of each revolution, so 25 clicks corresponds to 12,5 cycles) this means that we should increase the dispensing percentage.

The fourth step will be to calculate the quantity of stock solution needed for one day:

  • The amount of stock solution needed will be equal to daily water consumption multiplied by the dispensing percentage:

- If it is 2% it will be: 800 liters/day x 0,02 = 16 liters
- If it is 5% it will be: 800 liters/day x 0,05 = 40 liters

The fifth step will be to prepare the stock solution needed for one day:

  • We will mix 1.600 g of commercial product in 16 or 40 liters of water for every 24 hours.


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