So you may have always wondered… where do baby horses come from? In more than 20 years being surrounded by horses and riders, I have occasionally been surprised to hear this question from beginners in the field.
Well, here’s the answer…
Horses are born live like most mammals, and are not hatched from eggs. Following mating between a male and female, the mare (female horse) is on average pregnant for 11 months. The foal is then born live, and is able to stand and walk almost immediately following the birth.
So the answer is an emphatic no – horses do not lay eggs! But why not? Why have they evolved the way they have? And what other key tips and facts do you need to know about horses and birth? I’m going to answer all of these questions in this article, and give you the full facts about horses, eggs, and everything in between.
Do All Mammals Give Birth to Live Young
To assume that all mammals give birth to live young would be surprisingly incorrect. It is true that most mammals give birth to live young which normally sets them apart from others mammals. However there are five species in the world known as monotremes that are mammals that lay eggs instead of giving birth to live young.
The only currently existing monotremes are located in New Guinea and Australia. They are different from other mammals not only because they lay eggs, but also because they have no teats. The animals of this select group are as follows:
- Western Long-Beaked Echidna
- Eastern Long-Beaked Echidna
- Sir David’s Long-Beaked Echidna
- Short Beaked Echidna
- Duck-Billed Platypus
Anyway – enough about that… back to horses.
Advantages to Laying Eggs
Although horses don’t lay eggs – there would be some advantages if they did. To begin with, laying eggs lets mom be free to roam about and hunt and feed herself without having to endure longer periods of gestation. Since mom isn’t carrying a baby (or babies) inside her, it would be much easier for her to also be quick on her feet and escape if a predator tried to get her.
Eggs don’t need a ton of maintenance after they are laid. Really they need to be out of sight as much as possible and to be kept warm. Mom can do this by picking a secluded area away from open view, or simply covering the eggs with vegetation.
Covering the eggs with soil or plants is also a great way to keep the eggs warm if mom doesn’t want to occupy too much of her time sitting on top of the eggs to keep them warm .
Laying more eggs gives a lot of options for there to be living offspring. This could potentially overcome eggs that are victimized by predators, or eggs that are damaged or genetically abnormal and don’t produce healthy offspring. [Source]
Advantages to Giving Live Birth
Giving birth to live young allows the mother to keep her baby or babies safely inside to develop. What she may personally sacrifice as far as her own mobility and safety is concerned, is a trade off for more concrete security for the developing fetus. Babies inside can really grow freely without much fear of being injured (except if mom is).
These babies can also be moved from place to place, especially if a territory becomes unsafe or suddenly lacks resources. This is especially advantageous in that mom receives the best nutrients to transmit to her foal, versus eggs which more or less stuck in one place even if the environment changes.
Because mom is able to keep baby inside and away from predators, the offspring is able to mature and grow and is much more developed to better survive outside the womb. These offspring tend not to only be more developed, but possess more intricate and organized body and organ systems.
This could be advantageous as baby would be better suited to immediately start traveling with the herd. Since horses cover a lot of miles per day, baby literally needs to hit the ground running. Having more time in the womb to develop makes baby and easy addition to the herd.
Since baby can run and be quick on its feet, it’s not as vulnerable to predation and this can give the baby better chance of surviving to maturity. [Source]
Why Don’t Horses Lay Eggs
Well this was a hard question to research. Frankly I could not really find the perfect research on this, but what I could find I think is just the right amount of science plus Captain Obvious.
- Horses are Nomads
Wild horses tend to graze and travel all day long for be able to have sufficient food and water. On average wild horses could travel 10-20 miles a day. If horse laid eggs, mom would have to expend a lot of energy traveling with the herd and then coming back to her nest.
What if the area she had originally picked out to lay her eggs was now dangerous and lacking resources? Again, no way for her to pick up her eggs and bring them with her. The herd would want to move on and probably find a different territory with better food and water availability. Mom would have to choose between being vulnerable and potentially starving to death, or leaving her eggs to fend for themselves.
- Horses are Heavy
The average horse can weigh anywhere from 900 to 2000lbs depending on the breed of horse and of course their own individual genetics. To put that in perspective, a Black Rhinoceros – yes I said it a Rhino – weights around 2000 lbs.
Ok now imagine an egg. I would imagine if horses DID lay eggs, they would not be like your average egg you see in a bird’s nest. They would more than likely have to be somewhat proportional to the size of that horse.
So you will have to use your imagination with me on this one. Since we don’t have real factual data on these factious horse eggs… I had to be creative.
- Theoretical Egg Size and Amount of Force to Break The Egg
We will use an extreme example and pick a swan egg. A swan egg requires about 26 lbs of pressure to break. Your average swan egg is roughly 340g in weight and your average mute swan weighs about 24-26 pounds. When birds lay on their eggs, they are supporting most of their weight add the space between their thighs and their body is a soft cushioned area where the eggs can be kept warm [Source].
Now if you use the same ratio of mom to egg for a horse you can take the average 1100 pound horse having a 34.35 pound egg! Using the same math, if we calculate using the same ratio again for how much force it would take to break a “horse egg” the final number is 1191 pounds.
Unlike birds, I can’t picture horses support their weight crouching down to the ground to rest on a 35 pound egg in between their thighs… I know this is all hypothetical, but when you compare the two – it’s pretty clear horses would not be great egg layers.
Horses Giving Birth to Live Young
The gestational period for mares (female horses) can vary between 320-370 days [Source]. Can you imagine nearly an entire calendar year being pregnant and developing their offspring?!
This requires a lot of energy and commitment on mom’s part and thus when she does give birth, baby sticks around with mom for quite some time. Unlike some species like rabbits, who are almost completely independent from mom after just a couple short weeks, foals in the wild have been known to nurse for up to a year!
Mammals and Eggs
So the well known fact kids are taught “all mammals give birth to live young” is absolutely not always 100% true. It is a decent generalization, but it is truly not absolute.
As far as horses are concerned, there may be several more scientific ways to examine why they don’t lay eggs. Instead, you can think about horses you may have observed in your own barn or in the wild. Through these observations, you can easily deduct reasons by what you see versus attempting to chase down answers through mounds of research.
A lot of the reasons why humans are humans, dogs are dogs, and horses are horses, are due to several hundreds of years of adaptation, survival of the fittest, and natural genetic modification/mutation that has been preserved over time.
So it’s possible to say there may come a day where enough evolutionary change occurs where horses do lay eggs….but it is still extremely unlikely!
Do Any Mammals Lay Eggs? Wonderopolis. (n.d.). https://wonderopolis.org/wonder/do-any-mammals-lay-eggs.
Reflections in Nature: Eggs vs. live young. sungazette.com. (n.d.). https://www.sungazette.com/uncategorized/2018/05/reflections-in-nature-eggs-vs-live-young/.
Staff, K. E. R. (2020, March 11). Gestation in Mares: What Is Premature? What Is Overdue? Kentucky Equine Research. https://ker.com/equinews/gestation-in-mares-what-is-premature-what-is-overdue/.
Vanover, L. (2021, January 9). 12 Extraordinary Bird Egg Facts. Birds and Blooms. https://www.birdsandblooms.com/birding/eight-extraordinary-facts-about-bird-eggs/.