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close this bookRestraining Animals and Simple Treatments (IIRR, 1996, 53 p.)
View the document(introduction...)
View the documentForeword
View the documentRestraining animals
View the documentPhysical examination
View the documentParaveterinary kit
View the documentDosages
View the documentCommon units of measurement
View the documentReading drug labels
View the documentEstimating live weight
View the documentAdministering medicine
View the documentEmergency procedures
View the documentWhen to call a veterinarian
View the documentGlossary


How much medicine should you use?

The amount of medicine to use depends an several factors:

- The type and stage of the disease. Generally, more severe cases need more medicine.

- The species and weight of the animal. Larger, heavier animals usually need more medicine than small or young ones.

- The type and composition of the medicine. Medicines come in different formulations. Plus, the formulation might vary between brands of the same type of medicine and from country to county.

What is important is not the weight of the tablet or the amount of liquid, but the amount of the active ingredient. Same tablets contain 5 mg of the active ingredient, diners contain 10 mg or more. You might have to mix some medicines yourself from powder or concentrated solution.

Active ingredients

The active ingredient in a medicine is the substance that does the work of curing or preventing the disease.

In addition to the active ingredient, medicines might also contain water, a binder to make the medicine stick together in a tablet, and other ingredients.

Some medicines have more than one active ingredient (such as penicillin streptomycin, which contains two antibiotics: penicillin and streptomycin). Check to make sure that both can be used for a particular problem.

Measuring active ingredients

The amount of active ingredient in a medicine is normally measured in milligrams.

For liquid medicines, the concentration of active ingredient is normally given in milligrams of the ingredient per milliliter of the medicine (mg/ml).

For tablets and capsules, the concentration is normally given in milligrams per tablet or capsule.

Antibiotics and vitamins are sometimes measured in special units, called International Units or IU instead of milligrams.

Read the label

Because of these variations, it is not possible to give a firm general rule on how much medicine to use. However, here are some guidelines.

Read the label on the medicine carefully. (If you bought the medicine without a label, ask the store owner for instructions.) Follow the directions on how much medicine to use, how to apply it and how often to repeat the treatment. The section Reading drug labels on page 19 gives an example of a typical label.

The medicine label might tell you to apply a certain amount of medicine per kilogram of the animal's body weight. Use the tables on pages 20 to 23 to estimate the bodyweight.

If you are not sure how much medicine to use, or how to apply it, ask someone with more experience. Veterinarians, experienced livestock raisers and the owner of the store where you bought the medicine are good sources of information.

Applying the wrong amount

It can be dangerous to apply either too little or too much of a medicine.

- Applying too much medicine can harm or even kill the animal.

- Applying too little medicine can have at least two consequences:

- It might fail to cure the problem.

- The disease organisms might become resistant to the medicine. This makes the disease more difficult to treat.

This is especially a problem if you stop treatment early, before the recommended time is over (for instance, if the animal seems to be recovering but still carries the disease bacteria). Some bacteria might survive and be more resistant to the medicine next time.

Remember: use only the recommended dosages, and follow the instructions fully.

Follow the law

Laws in many countries prohibit non-veterinarians from treating animals with certain types of medicine, for example antibiotics. These laws aim to avoid harming animal and human health and to prevent misuse through ignorance.

Calculating dosages
Some medicine labels tell you very clearly how much medicine to
apply for a certain type of animal.
Example (from the medicine label)
Dosage Piglets 1.0-2.0 ml (1st-4th day of life)
Calves 4.0-8.0 ml (1st week of life)
Such cases are easy: just follow the instructions on the label.

Calculating dosage based on body weight Other labels require you to do some simple arithmetic. You might have to calculate the amount of medicine required from the body weight. Example (from the medicine label)

Dosage 1 ml/10 kg body weight If your animal weighs 90 kg, you should apply 9 ml of the medicine. (See the tables on pages 20 to 23 to estimate the body weight.)

Calculating dosage based on active ingredient

Sometimes, the label tells you only the concentration of active ingredient and the amount of active ingredient to apply per kilogram of bodyweight. You must calculate the amount of medicine to use. This takes a little more arithmetic (a pocket calculator can come in handy). Here's how to do it:

First, measure or estimate the body weight of the animal.


A sick cow has a girth of 120 cm.
The table on page 20 shows that this animal weighs about 150 kg.
Calculate the amount of active ingredient you need to use.

The medicine label says the dosage is 20 mg/kg body weight/day.

- Animal weighs 150 kg

- Dosage = 20 mg/kg body weight

- 20 mg/kg x 150 kg = 300 mg of the active ingredient. Check how much active ingredient the medicine captains.


The medicine label says that each 5 ml (I teaspoon) contains 125
mg of dihydrostreptomycin sulfate.

- Therefore, 1 ml of the medicine contains 25 mg of dibydrostreptomycin (the active ingredient). Calculate how much medicine contains this amount of active ingredient.


- 1 ml contains 25 mg of dihydrostreptomycin.

- You need 300 mg of the active ingredient. - Therefore you need 300/25 = 12 ml of the medicine.