Determining the correct dosage of medication for animals—whether traditional livestock, exotic hoofstock, zoo animals, or any animal in a capture situation—is critical for animal health and safety.
Dosages are typically based on the animal’s weight, which can be estimated or measured using different methods depending on the species and the industry. For those with farmed use. Most livestock operations have scales utilized when animals are being run through the chute for routine care. Accordingly, weight, age, and any procedures or medications given should be recorded at that time.
Tips on Calculating Dosages
To correctly calculate the drug dosage required to immobilize a particular animal, the worker must know three factors:
- Estimated or actual weight of the animal. If the weight is estimated in pounds (lbs.), it should be converted to kilograms (kg), as dosages are expressed in mg/kg (milligrams of drug per kilogram of body weight). One pound equals 0.454 kg, therefore the conversion is calculated by multiplying the estimated pounds by 0.454. Thus, a 100 lb. animal weighs 45.4 kg. Because 1 lb. is nearly equal to 1/2 kg, a simpler conversion can be made by dividing the estimated weight in pounds by 2. Because of the difficulty in accurately estimating an animal’s weight and the safety margin of CNS drugs, this simpler conversion is acceptable for fieldwork.
- The dosage recommended for the species. This refers to the dosage recommended to produce immobilization in a particular species. Dosage recommendations may be provided by a veterinarian, via the drug package insert, or by consulting dosage tables in reference literature. The suggested dosage tables are given in mg/kg.
- Concentration of the drug used. The concentration (solution strength) of the drug is listed on the label of the vial, on the package, and in the package insert. It is given as mg/ml (milligrams of drug per milliliter of liquid volume). To minimize the drug volume and consequent size of the RDD, the highest available concentration of a given drug should be used.
For all practical purposes, 1 ml (milliliter) is equal to 1 cc (cubic centimeter) of liquid volume. Based on these three factors, the drug dosage is calculated as follows:
Animal weight (kg) x dosage (mg/kg) / concentration of drug (mg/ml) = drug volume in ml or cc
The way an injectable may affect an animal, and the level of immobilization produced are subject to several factors. In addition to the animal’s weight, its age, sex, physical condition, and physiological state at the time of injection, will have varying degrees of sensitivity to the medication. This can produce different and unexpected results from one animal to another, even within the same species.
Tools for Calculating Dosages
There are some free online calculators to assist with figuring out the proper dosage for your animals. There are also several apps that can be downloaded to your mobile device for quick ease of use.
Please see below for some general suggestions and species-specific examples:
Cattle:
- Once the weight is determined, dosages are calculated based on product labels, which provide guidance for weight-specific dosing (e.g., 1 mL per 100 lbs. of body weight).
- Example: If a cow weighs 1200 lbs. and the dosage is 1 mL per 100 lbs., the correct dose would be 12 mL.
Sheep and Goats:
- Dosages for sheep and goats are usually lower than for cattle, and correct weight determination is essential due to their smaller body size. Medications may be dosed at rates like 0.1-0.5 mL per kg (2.2 lbs.).
- Example: A 100 lb. goat with a dosage rate of 1 mL per 10 lbs. would require 10 mL of medication.
Swine:
- Because pigs can vary greatly in size, accurate weight determination is crucial. Dosing is often in mg per kg or mL per 10 kg.
- Example: If a pig weighs 220 lbs. and the dose is 1 mL per 20 lbs., the dose would be 11 mL.
Deer and Elk:
- Since cervids can vary in size, accurate dosing is essential. Overdosing can lead to significant health risks, and underdosing may render treatments ineffective. Dosages are typically calculated in mg per kg or mL per kg.
- Example: A 400 lb. elk with a dose of 0.5 mL per 10 lbs. would require 20 mL.
Poultry:
- Medications are typically administered via feed or water. Dosage is calculated based on the average weight of the birds and the total number of birds being treated.
Example: If 100 broilers weigh an average of 5 lbs. each, and the medication is dosed at 1 mL per 5 lbs., 100 mL would be required for the entire flock.
Veterinarian Guidance
A veterinarian should always be consulted to ensure the correct dosage, especially when weight estimates are used, as under- or over-dosing can have serious consequences. Having a current Veterinarian-Client-Patient Relationship (VCPR) is critical for the health of your herd as well as proper dosing in any situation.
According to the American Veterinary Medical Association, a VCPR is present when all of the following requirements are met:
- The veterinarian has assumed responsibility for making clinical judgments regarding the health of the patient, and the client has agreed to follow the veterinarian’s instructions
- The veterinarian has sufficient knowledge of the animal to initiate at least a general or preliminary diagnosis of the medical condition of it. This means that the veterinarian is personally acquainted with the keeping and care of the animal by virtue of a timely examination by the veterinarian, or medically appropriate and timely visits by the veterinarian to the operation where the animal is managed
- The veterinarian is readily available for follow-up evaluation or has arranged for veterinary emergency coverage and continuing care and treatment
- The veterinarian provides oversight of treatment, compliance, and outcome
- Patient records are maintained
The VCPR is defined in Section III of the AVMA’s Principles of Veterinary Medical Ethics. This document also includes a description of how the VCPR may be terminated.
Each state may choose to further define and make requirements for large operations when establishing a VCPR.
Precise medication dosing is crucial for maintaining animal health and safety across various livestock and wildlife species. Accurate weight estimation, proper dosage calculation, and species-specific considerations are essential for effective treatment. However, these technical aspects should always be complemented by professional veterinary guidance. Establishing and maintaining a strong Veterinarian-Client-Patient Relationship (VCPR) is paramount for ensuring the well-being of your animals and the success of your operation. By combining accurate dosing practices with expert veterinary oversight, livestock owners and wildlife managers can provide optimal care for their animals, promoting health, productivity, and welfare in their herds or populations.