How Veterinarians Use Math on a Daily Basis


Have you been sitting in a math class wondering how you are ever going to use this knowledge in real life? Almost all of us have wondered that at some point. If you are considering a career as a veterinarian, then you may be interested in learning just how much math you will really be using on a regular basis.

Veterinarians use math frequently in order to calculate drug dosages, determine caloric/nutrition requirements for animals, figure out fluid rates, and more. Most of this math involves foundational skills and knowledge learned in algebra classes.

But that doesn’t mean that it isn’t worth it to learn calculus. You can still stretch your brain and solidify your current math knowledge by taking advanced math classes. But this article isn’t about calculus, so let’s take a look at some of the common math formulas that veterinarians use on a day to day basis.

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Calculating Medication Doses

As a small animal veterinariann, I use a book called Plumb’s Veterinary Drug Handbook (<-amazon link) to help me determine how much medication a specific animal should have. Most doses in this book are listed as mg/kg. That means that a pet should have a certain amount of milligrams of the medication per a kilogram of body weight.

Since I work in the United States, we weigh most of our patients in pounds. So the first thing I need to do is convert pounds to kilograms.

1 kilogram = 2.2 pounds

So to figure out how many kilograms a 22 pound dog is, I divide 22 by 2.2.

22 / 2.2 = 10

So this dog weighs 10 kgs. To help you understand how this works, check out the video below.

Okay, now that I have the dog’s weight in kilograms, I can use a mg/kg dosing recommendation to come up with the number of milligrams of medication a pet should have. For example, maybe I want to prescribe an antibiotic like cefpodoxime. That medication is recommended to be prescribed at a dose of 5mg/kg every 24 hours.

So now I take 10kg * 5mg/kg =50 mg.

The smallest size tablet I have of cefpodoxime is 100mg. So I also need to divide 50 mg by 100mg to get 0.5 (or 1/2) to figure out how many tablets to give this dog per dose. After all of that math, I will prescribe this 22 pound dog 1/2 of a cefpodoxime tablet once daily for 14 days.

Interested in learning more, check out this YouTube video all about veterinary pharmacology calculations.

Calculating Nutrition Requirements

Another common calculation for veterinarians is figure out a pet’s calorie requirements. Obesity is a big problem for pet dogs and cats, so it is important to help pet caretakers calculate how much to feed a dog or cat.

The most commonly used formula to calculate a “resting energy requirement” or RER is below:

RER = 30 * (animals weight in kg) + 70

Resting energy requirements help calculate a baseline number of calories a cat or dog needs to consume during a day. Once you have the RER, you can make your estimate a little more accurate by multiplying the RER by the number that corresponds with the estimated daily energy needs for certain categories of animals.

For example:

Neutered adult=1.6 x RER
Intact adult=1.8 x RER
Inactive/obese prone=1.2-1.4 x RER
Weight loss=1.0 x RER for ideal weight
Puppy 0-4 months=3.0 x RER
Puppy 4 months to adult= 2.0 x RER

So for my 40 pound dog Glia, 40 lbs * 1kg/2.2 lbs = 18. 2 kgs.

18.2*30 = 546

546 +70 =616

This means that Glia’s RER is 616. She is a spayed (neutered) female dog. So I will multiple 616 *1.6 = 985.6 kcals.

In order to maintain her weight, she will need around 985 calories per day.

You can find out more about calculating calorie requirements for dogs and cats at Pet Nutrition Alliance or Ohio State University: Veterinary Medical Center.

And if you want some more examples of how this correlates to real-life feeding recommendations, head over to my TurboPUP meal bar review on PawsitivelyIntrepid.com. About 1/2 way through the article, I discuss calculating how much to feed my dogs while hiking and backpacking and discuss the math behind the numbers.

Calculating Constant Rate Infusions and Fluid Rates

Some of the more challenging math a veterinarian is expected to have mastered is calculating constant rate infusions. A constant rate infusion (CRI) is a medication that is continuously administered to a patient over a period of time.

Depending on the veterinary facility, the medication could be administered without dilution, calculated to be mixed with concurrent IV fluids already being delivered at a set rate, or prepared with a separate bag of IV fluids that can be titrated at a different rate from the main fluid bag.

When calculating the addition of a medication to a bag of fluids, it is important to know the CRI dose (mg/kg/day), the concentration of the medication, and the hourly fluid rate.

There is no simple formula for this type of calculation, so if you are interested in some specific examples click on one of the links or watch the YouTube video below.

  • The Veterinary Nurse or Vet Tech Prep will both walk you through how to set up a constant rate infusion for metaclopramide added to fluids running at a pre-set rate.
  • Vet Times has created a pdf with several examples of CRI calculations.
  • And this YouTube video by David Liss discusses how to calculate a CRI.

Another way that math is used with fluid calculations, is when creating fluid dilutions, such as when needing to run a diluted dextrose fluid for a dog that is hypoglycemic.

For fluid dilutions, there is another set formula that can help you out.

C1*V1 = C2*V2

David Liss has another great video for how to use this calculation to figure out how to mix fluids to create a 5% dextrose solution.

Yes, Veterinarians Use a Lot of Math

Whether or not you need to know the above calculations yet, I hope the examples above make it obvious that veterinarians need to have a good grasp of math. Good math skills and attention to detail allow veterinarians to accurately dose medications and make good nutritional recommendations. These math skills can be the difference between saving a life and ending a life.

So as you sit in your current math class, pay attention. The knowledge you learn here is just as important as what you learn in your biology class.

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