Do Human Pregnancy Tests Work On Horses? (Important Facts)

By Zunnun Ahmed •  Updated: 09/04/22 •  10 min read

Since human home pregnancy test kits are easy and provide accurate results, many think of applying them to horses. But do human pregnancy tests work on horses? Well, they don’t.

Let’s see where the confusion starts. The home pregnancy kits detect the presence of pregnancy hormones in the urine sample of a pregnant woman called Human Chorionic Gonadotropin (hCG). Interestingly, horses are the rare mammals that secrete the Chorionic Gonadotropin while pregnant, known as Equine Chorionic Gonadotropin (ECG).

Since both have a similar pregnancy hormone, many think they can be tested with the same kit. But it doesn’t work that way because these hormones are actually distinct. If you want the details of how pregnancy tests for both these living beings work and how they differ, continue reading the article here.

Why would someone want to know if a horse is pregnant?

People involved in the equine business or equine reproduction need to know whether their mare is pregnant. Businesses like horse farms depend on horse breeding, which helps them make money by producing more horses and trading them.

Some also like to have horses at home, especially in their farmhouses. And when the 2018 Farm Bill officially designated horses as livestock, many animal lovers started keeping horses in their homes as companion animals. It has led many horse owners to breed horses and get more foals.

So knowing whether a mare is pregnant or not has become very important. Horse breeding requires extra care and proper feeding of the breeding stock. There’s generally a vet who regularly checkups the horses, including mares who might be expecting.

But we’ve seen many enthusiastic owners who want to try different home tests to determine horse pregnancy. So, they’re generally curious about the success of human pregnancy tests on horses.

How do human pregnancy tests work?

The human pregnancy tests, whether done in a doctor’s lab or a home pregnancy kit, use the same mechanism to determine pregnancy. It works by diagnosing the urine for a hormone called Human Chorionic Gonadotrophin (HCG). This hormone is made in a woman’s body only when pregnant.

When a fertilized egg attaches to the uterus lining, only then does the HCG get released. People used to doubt the reliability of the home pregnancy test kits earlier, but with 99% accuracy, they’ve become equally reliable as the urine pregnancy test done at the doctor’s office.

However, the test can be inaccurate if it’s not used correctly or if the kit is expired. So, it requires one to follow the instructions carefully for an accurate result.

Since a home pregnancy test kit is so easy to use, many wonder whether it works on other animals, especially pets or livestock. Here we’re referring to the horse owners thinking of using the human pregnancy test kit for their horses. Will it work? We’ll find out.

Also see: Horses are known for their strong and durable hooves, but are they good for dogs? We’ll explore the benefits and drawbacks of giving your dog a horse hoof.

Do human pregnancy tests work on horses?

According to a recent study, Chorionic Gonadotropin (CG) is a significant sign of establishing pregnancy in humans and a few other primates (the group of extant mammals that include apes, monkeys, and lemur). The study also finds that this Placentally Expressed Hormone is absent in most mammalian orders.

However the study mentions one exception. And that horses have evolved Chorionic Gonadotropin (CG) independently from primates, referred to as Equine Chorionic Gonadotropin (ECG) and previously known as Pregnant Mare’s Serum Gonadotropin (PMSG).

They have also evolved unique and specialized placental structures (endometrial cups). It delivers ECG to the bloodstream of the mare between 40 to 130 of their gestation.

Since both humans and mares have gonadotropic hormones produced in their chorion during pregnancy, these technical discussions lead us to one long question: “Can the mechanism that detects hCG levels for humans also detect ECG for equines?”

What are the challenges of using human pregnancy tests on horses?

Why human pregnancy tests don’t apply to horses, and what are the challenges? The simple answer would be that scientists haven’t developed a common human pregnancy test that works on horses or other animals.

But if you want to know about the challenges in detail, here we’ve got you covered with some crucial information.

pregnancy tests on horses

[1] The difference in composition & pattern of chorionic gonadotropin

The chorion gonadotropin, in all cases, has two subunits, such as alpha and beta. While alpha is common to every glycoprotein hormone, beta differs in species and is more hormone-specific.

Although placental CGs or Pituitary LH (Luteinizing Hormone) in equids such as horses, zebras, or donkeys are produced from the same gene and have similar protein sequences, they differ from that of humans.

The most significant difference is the carbohydrate side chain in their respective beta subunits, which is different for all species.

See also: If you’re thinking of buying a horse, you’re probably wondering why they’re so expensive. Here are 11 reasons why horses are expensive, plus tips on how to save when buying one.

[2] Collecting horse pregnancy hormone (ECG) is more complicated

Testing horse pregnancy by measuring Chorion Gonadotropin differs greatly from modern human pregnancy tests. In humans, it’s done (hCG is tested) mainly using urine samples, while ECG is usually collected from the blood sample of the mare.

The horse sample collection is also complicated and isn’t as convenient as humans’. The ECG starts to get produced in the pregnant mare’s uterus between a limited period of 40 to 130 days of gestation.

The endometrial cups produce this hormone and deliver it to the mare’s bloodstream. An experienced vet collects the serum from the blood sample and sends it to the reference laboratory for testing. So it’s a tedious process, unlike human pregnancy testing, and can’t be made easier when ECG hormone is tested.

There’s also criticism from the Swiss-based Animal Welfare Foundation for inhumanely obtaining ECG from horse blood across some Latin American horse farms. But that’s not for pregnancy testing in most cases.

[3] Horse pregnancy hormone is unreliable for testing

The horse’s pregnancy hormone ECG test isn’t as accurate as the human pregnancy hormone hCG test. The false-positive reactions are common for a mare’s pregnancy hormone (ECG) test with a commercially available mare-side kit. Let alone the human pregnancy test kits.

The accuracy of the mare pregnancy hormone test also becomes questionable if pregnancy is lost and endometrial cups are still functional. Besides, false negatives are common for ECG hormone tests when mares curry mule fetuses or ECG concentrations tend to decline.

So the pregnancy hormone, Chorionic Gonadotropin, is different in nature for both humans and horses. So testing them with a common procedure isn’t possible.

See also: If you’re struggling to connect with your horse, this article is for you. Learn why horses may not like you and what you can do to fix the issue.

[4] Horse pregnancy primarily depends on a different substance

The pregnancy test for horses depends primarily on a different substance than Chorionic Gonadotropin. It’s pretty evident from the research outcome of Dr. Henderson and his team from the Reproduction Group at the Hopkirk Research Institute at Massey University.

They initially developed a lab blood testing procedure for mare pregnancy testing. According to their research, what differs from human pregnancy testing is that mares have Estrogen Estrone Sulphate in the blood and urine, which is their primary pregnancy determiner. Baseline Progesterone Levels are also useful in detecting a mare pregnancy primarily.

The research also finds that the pregnancy determiner Estrone Sulphate is found in the mare’s urine and blood. Since urine is non-abrasive and breeders can easily collect the sample, including home pregnancy kits for horses is a blessing for the breeders.

These tests provide a more reliable horse pregnancy test than the Chorionic Gonadotropin test, the hormone that’s common in humans and horses. So trying human pregnancy tests on horses is somewhat pointless.

What’s the usual way to determine pregnancy in horses?

Horses typically mate between spring and summer. So if you’ve got a breeding mare or it has come in contact with the stallion during the mating period, you’ll want to find out whether she’s pregnant.

You’ve seen that human pregnancy tests don’t work on horses. So here we’ve got the usual ways to determine a horse pregnancy.

Checking with non-chemical methods

These are more traditional methods that don’t use chemical lab tests to determine the mare’s pregnancy. The common methods include:

Checking with chemical methods

Now let’s see what chemical methods are used to test a mare’s pregnancy.


Every breeding farm has a schedule for determining the pregnancy of its mares. They rely more on professional methods that are well-established to determine the pregnancy status of their horses. So it’s less likely for them to use or think about human pregnancy tests for their horses. However, some small farms or people who keep horses as livestock might sometimes consider a Do-It-Yourself method to determine their animal’s pregnancy.

They wonder “Do human pregnancy tests work on horses?” They don’t. It’s because the pregnancy hormone has a different composition for both these beings, so the testing requires different techniques. Also, there could be inaccurate and unreliable results if the same method is applied. So it’s pretty evident that the human pregnancy tests don’t work on horses or any other animals.

Zunnun Ahmed

We are a group of horse enthusiasts. We want to provide information and tips to help others learn more about horses, how to care for them, and how to enjoy them.

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