This assumes that dosage is expressed in mass per unit body weight (e.g., mg of drug/kg of body weight) and you know the weight of the animal (e.g., in kg). Just multiply the two numbers together and you will know the amount of drug (e.g., mg) to administer to the animal.

@ Gordon L Warren

thank you for your answer

But the amount of water that I add to the drug after determining its quantity during oral dosing, how do I determine it

Having to correlate the dose with human body. A preliminary work to estimate human doses to work with human bodies...