Hens don’t need a rooster to lay eggs, but they do need a rooster in order to lay fertilized eggs. Chickens are different from mammals in a lot of ways when it comes to their anatomy and therefore their reproductive system. Let’s talk about how eggs are fertilized by chickens.
While you don’t need to do much in this process, it’s very interesting!
When roosters mate with hens, they transfer their sperm through cloacal contact and not by penetration. The first fertile egg is laid between 36-48 hours after mating. So an egg laid the day the chickens mate won’t be fertile and an egg laid three days later is fertile.
What is The Cloaca?
A hen has just one opening where both feces and eggs exit the body. This is also where sperm enters. The rooster’s cloaca passes feces and transfers sperm to the hen.
Chickens don’t urinate! They don’t have bladders or urethras, liquids exit with their poop through the cloaca. Since they don’t produce liquid urine their chicken coop is able to stay dry much easier than if they were soiling their bedding all day. Their liquid feces are able to dry quickly.
When the hen and rooster make cloacal contact, sperm enter the oviduct and are stored in glands that can store over half a million sperm. Sperm can stay alive in the storage glands for up to 3 weeks fertilizing eggs. An egg is fertilized about 24 hours before it’s laid.
How eggs are fertilized by chickens is more similar to mammals than you might think. Considering the fertilizing happens inside of their body even though the growing happens outside of their body!
What Mating Looks Like
Before a rooster mates with a hen he will prance around her and cluck. When he mounts the hen, he bends his tail down and the hen will lift her tail up. The cloaca vents will press together and the rooster injects his sperm.
Do Fertilized Eggs Look Different?
Fertilized eggs do not look obviously different upon first examining them. Without cracking the egg, you can shine a light into the egg and see spider veins and a dark area if the embryo has started to develop. An egg that hasn’t been fertilized will look translucent.
When comparing the yolks inside of the eggs (after cracking them open), you can look for the germ spot. The germ spot is a white circle just outside of the center of the yolk. A fertile egg will have a larger white spot with a clear space in the center. An infertile egg will have a smaller white spot. This can be hard to identify if you aren’t comparing a fertile yolk with an infertile yolk.
How Fertilized Eggs Develop Into Chicks
After a fertilized egg is laid, it will only develop into a chick if it’s kept warm. Depending on a lot of factors (we will talk about this soon), a hen doesn’t always have the desire to incubate the eggs. It’s a big job! She will sit on the eggs for the majority of the day to keep them warm.
Incubating the chicken eggs yourself is a 21-day process that involves keeping the eggs at a certain temperature and humidity level, as well as turning the eggs!
After a week of incubating you can shine a light and see the veins and embryos forming as we previously mentioned.
If fertilized eggs aren’t incubated they won't develop into chicks. A hen will look for a comfortable stress-free place to lay her eggs and incubate them. Nesting Pads are a great addition to the chicken coop.
Why Do Some Hens Not Incubate?
Many chicken breeds have been bred for laying eggs for consumption and the genetic trait to incubate eggs isn’t needed (or wanted) when you have chickens so you can eat their eggs.
For this reason, some breeds are less likely to want to incubate their fertilized eggs. Age is also a factor in whether or not a hen will be broody. Chickens usually need to be at least 2 years old before they want to take on the job of incubating their eggs.
There are also certain times when a hen’s hormones kick in to where she wants to raise chicks! It’s normal for even the broodiest hens not to incubate eggs all the time.
How Eggs Are Fertilized By Chickens
Only about 60% of mating (successful copulation) results in fertilization. The number of fertile eggs that will result from a single mating ranges from 1 to 11. So, even though hens lay eggs every few days and the sperm from a rooster stays alive for weeks, only about five eggs will result from one copulation with a rooster.
It may seem like there are lots of eggs with only a few chicks. That’s usually the way you want it though!
We are not veterinarians, and none of our information should be construed as veterinary advice.
Before adding any new product, please consult your exotic veterinarian. If your pet is acting unwell and you have concerns for their well being, please contact your vet immediately.
