Complete Guide to Freemartin Cows (What Are Freemartins?)

There aren’t many things about cattle that humans don’t already know. After all, we’ve been farming cows for thousands of years. But, there is one strange occurrence in cattle that has perplexed and terrified farmers for centuries: Freemartins.

Freemartins are a quirk of nature, they are a special type of female cow born with masculine features. Freemartins are formed when a male and female cow are born at the same time. Freemartins are female cows with uncharacteristically masculine traits. They can not give birth, don’t produce milk, are more muscular, and more aggressive than regular heifers.

In this article we’re going to look at freemartin cows in more detail, learn what they can and can’t do, how freemartins come to be, and what farmers do with them.

Guide to Freemartin Cows

What Are Freemartins?

A freemartin is a female cow (heifer) that is born alongside a male twin and has physical and behavioral masculine traits, caused by the male hormones produced for their twin in the womb which physically affect the heifer’s development.

Freemartins are both physically and psychologically masculine, although they are still biologically female. They can’t give birth, they are more aggressive, they are more muscular and can not become pregnant or produce milk, and their reproductive organs are smaller.

How Do Freemartins Develop?

Farmers have known about freemartins for thousands of years, but it wasn’t always understood how they came about.

It wasn’t until the year 1779 that scientist John Hunter discovered that freemartins were always the result of a twin pregnancy where the other twin was male.

Even today, scientists don’t fully understand the process, but it’s understood that male hormones present in the shared placenta affect the development of the female reproductive system, creating a freemartin heifer.

Freemartinism is a result of a male and female twins sharing the same placenta. It’s a natural biological process and is impossible to prevent, short of aborting all twin births.

Read More: How Many Times can a Cow Give Birth?

Characteristsics of Freemartin Cattle

Freemartins have typically masculine characteristics, which is unusual for a heifer. Although they are biologically female, there are physical as well as behavioral differences which set them apart from their heifer sisters.

Let’s take a look at some of the features of freemartins:

1: Freemartins Can’t Give Birth

Freemartins have non-functioning ovaries and so can’t get pregnant or give birth.

This is the most important characteristic of freemartins for farmers, since it affects how they can be used.

Since dairy cows need to be able to get pregnant to produce any milk, freemartin dairy cows who can’t produce milk are often sold for veal, or occasionally raised for meat instead.

Related Article: Does Milking Cows Hurt Them?

2: Freemartins have Smaller Reproductive Organs

Freemartins physical development is influenced by the male hormone AMH (Anti-Müllerian Hormone) which the female calf absorbs from her male twin. AMH inhibits the growth of the female reproductive organs inside the womb, sometimes to the point of non-functionality.

3: Freemartins are More Aggressive

Freemartins take on various characteristics from their male twin, not only physical but behavioral too. One such trait is aggression, which is higher in freemartins than in regular heifers.

Freemartins are sometimes kept apart from other females to reduce incidences of aggression. Dairy freemartins are likely to be kept with beef cattle since they can’t produce milk anyway.

Read More: Are Cows Aggressive?

What Do Farmers Do With Freemartins?

Freemartins are unusual, but they still have some value to farmers. 

Dairy freemartins are generally unwanted, due to their inability to get pregnant and thus their inability to create milk.

Although dairy freemartins are useless as dairy, they are still useful as meat. Dairy freemartins are either slaughtered as calves and sold as veal, or added to a beef herd and raised to adulthood.

Beef freemartins are unable to reproduce, but they can still be raised as beef just like any other heifer.

Many beef farmers choose not to allow their beef heifers to have calves anyway, so freemartinism isn’t a huge deal for beef breeds.

How To Tell if a Cow is a Freemartin?

The cost of raising a cow can exceed $850 per year, so it’s crucial for farmers to know if they have a freemartin on their hands so they don’t waste any money raising them.

There are several methods to test for freemartinism in cows, each with varying degrees of accuracy, complexity, and cost.

The most common freemartin test is to measure the cow’s reproductive organs. According to the University of Kentucky Dept of Agriculture, the vagina, uterus, cervix, and ovaries are underdevloped in freemartins, and this can be easily tested in young calves by using a measuring device.

For a more accurate approach (at a higher cost) there are scientific tests that can be carried out. 

Within the first three days after birth, the male Y chromosome can be detected in the blood of a freemartin with a simple genetic test called a PCR test.


To sum up, freemartins are female cows that are born sterile and with masculine physical characteristics and behaviors. Freemartins are sterile, more aggressive, and have smaller reproductive organs than regular heifers.

Freemartinism is detrimental in dairy farming because since they can’t get pregnant, they can’t produce milk.

Since freemartins can’t make milk, dairy freemartin calves are usually sold as veal, however beef freemartins can be raised to adulthood just like a regular beef heifer.

Although freemartinism can’t be prevented, it’s easy to test for freemartins with inexpensive genetic tests or crude tests that measure the depth of the reproductive organs.

Skip to content