How Much Penicillin Can You Give a Horse?

Jessica McDaniel
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What is the Purpose of Penicillin?

Penicillin is typically given to horses for active infections caused by bacteria. This is to treat the bacterial infection and make the horse more comfortable. The doses administered are determined based on the size, weight and the health level of the horse.

When people think of penicillin they are usually referring to penicillin G or penicillin V. These are the typical antibiotics administered to horses that are effective for all types of bacterial infections. Penicillin is sometimes also referred to as penicillin G procaine.

Who is Penicillin for?

If the horse is considered an outpatient (meaning it’s not an emergency), is being treated for an infection, and has normal kidney and immune system function, then penicillin is the treatment of choice aside from other pain relievers typically administered.

In the case of severe infection, penicillin is used as a preventative and it’s often administrated through the feed.

Phew! That’s a lot of information! What else can I tell you?

Here are some things you can read further about Penicillin and horse health:

Can I Freeze Medicines for Horses? – This article gives you all the essential information on freezing medicines in a safe way for your horse.

How Do You Give A Horse Penicillin?

Often, you'll need to give a horse penicillin to treat and prevent an infection. The process is almost identical to how you give a dog a pill, but there are a few extra steps.

The safest and most effective way to give a horse a medication is to mix the liquid medication with molasses to mask the taste and then hide the mixture inside the horse’s food.

Now, feed the horse its normal amount of food as if nothing has changed. A horse will not know it has swallowed the medication. This method takes a little longer, but it keeps the horse from feeling sick or feeling that it has taken the medication.

An alternative to mix up the medication and feed it to the horse, is to use a safer and easier pill gun. Open the horse's mouth and place the pill down the back of its throat. You also ideally want to restrict movement by tying the horse to a fence post. This makes it harder for the horse to spit out or accidentally bite the pill.

While oral medications are the easiest to administer, there are other methods that veterinarians sometimes use. Your veterinarian may also suggest dosage and frequency for injections, but this is not commonly used.

How Much Penicillin Should You Give a Horse?

Penicillin is a common antibiotic used to cure your horse of an infection. When treating a horse, the first thing you should do is to check the horse's weight.

If the your horse is less than 700 pounds, you should use 40-100 milligrams of penicillin per pound.

Over 700 pounds, use 300-500 milligram per pound.

If a horse is carrying 80 pounds or more of fluid in his gut (colic), use 500 milligrams of penicillin per pound.

A sick horse with an infection can't get better on an empty stomach, so make sure that he always has a full stomach of hay or another non-concentrated feed.

Unfortunately, it's not possible for you to accurately guess a horse's weight without a scale and measuring tape. That's why it's important to get to a vet or to pass by a farm supply store and have your horse weighed.

Penicillin For Horse

As per the CDC, “Penicillin is the antibiotic of choice for treating horses with suspected or proven Salmonella infections. Penicillin has an IC 50 of 0.080-0.167 micrograms/ml.”

The above mean that the bacterium is inhibited by penicillin at a concentration of not more than 0.14-0.17 micrograms/ ml. This concentration is achieved at amoxicillin dosage of 10-20mg per kilogram of body weight.


A quick search on Google determined that a 500g (17.5oz) bag of beef penicillin powder is roughly 2.5mg. A quick search on the web site of a company that deals in penicillin powders tells us that a 500g container contains 30,000 doses; that is to say a horse is given 300mg of penicillin per dose.

The next question is how much penicillin can a horse safely be given. The answer to that depends on the horse's size and general health.

When you give more than is suitable in one go, the bacteria will just become resistant to the drug and continue to multiply. Instead, you should give small doses at a time.

In the case of a horse with a high temperature, the bacteria causing the infection will continue to multiply and cause more severe symptoms. Therefore, the higher the temperature, the higher the dose that should be administered for a short time to help get the bacteria under control before the temperature drops to a normal level.

In the case of ulcers, the veterinarian may also use penicillin to prevent the ulcers from occurring. Ulcers can result from excessive stress.