Female only hatching eggs – Myth or Fact?

Female only hatching eggs – Myth or Fact?

There has been a lot if chatter across social networks and forums recently about hatching only female chicks. One entry, and one I responded too, asked, How can I hatch just female chickens? Whilst to the established breeder this appears a nonsensical question, however it has validity and mileage for discussion. Some of the responses, and I’ll cover these shortly, are based on myths. However do these myths hang true?

Firstly and most importantly we must understand the principal genetics which make up the resultant offspring. The germ(egg) and the sperm carry chromosomes which define the sex of fertilised germ. Unlike humans, where the sperm defines the sex, the opposite is true for poultry. All sperm carry the male (Z) chromosome, the germ contains either a male chromosome (Z) or a female chromosome (W).  The resulting fertilised germ will either be ZZ male or ZW female.

Sex Chromosomes

This is the only method that determines the sex of a chicken, environmental conditions, including diet, cannot change this! So why are there so many myths?

Let’s consider the artificial incubation environment factors which effect the success of a hatch. Temperature will affect the duration of a hatch, slightly high, chicks hatch early, lower and they hatch later. Obviously extremes of each will result in death of the embryo/chick. Humidity also impacts success, as well as good air flow.

Egg validity also key, shell quality, egg shape, egg size and egg structure are also factors, and let’s not forget sperm viability. Any significant deviation of the above will reduce the success of the hatch. Many of these factors will be influenced by the birds health, environment hygiene and diet. If we consider all the above we can understand the results of our hatches.

Cayuga Egg, Male or Female?

Cayuga Egg, Male or Female?

As I stated earlier sex is determined by chromosomes, however a myths exist about varying incubation temperature can change the sex of an embryo, We know is not true. But if we consider environmental factors, is it possible for temperature to influence the success rate of a particular bird sex. I.e if we turn temp up by 1 degree, could this kill off the weaker males and favour the female? Very unlikely but feasible. There is no research to support such a claim. If this were possible there is no doubt the hatcheries would have found the key and we wouldn’t kill 100,000’s of unwanted male chicks everyday.

A breeder claimed they set 12 eggs and incubated at a higher temp and got 8 females and 4 males and used this to support this myth. Research to support this would need to be conducted with 100,000’s egg in various hatches over the world to get some valid data. I draw on my previous statement “there is no research to support such claims.”

Male or Female?

Male or Female?

The second myth, hatching only round bottom eggs will result in females only. One breeder claimed he had worked in a hatchery for many years and found this method 99.9% successful. There is no link, logical or otherwise between the chromosomes in the fertilized germ and the shape of the egg. It’s the environmental factors and hen itself which shape the egg. A stressed bird or birds who are overstocked are more likely to produce misshapen eggs – fact.

Other breeders have claimed they have hens who produce female only off spring. This has far more merit, we know sperm only caries the Z chromosome and does not influence the sex, so it is feasible through genetics that a hen could produced female germs with only W chromosomes. The resulting offspring would all have ZW chromosomes and be female. Occurrence of such hens are few and far between, but not statistically impossible

Some will still doubt this and revert to the myth, what qualifications does a man from Lincolnshire have to write this? So, I don’t have any formal poultry qualification, But I do have an honours degree in Biology. I have studied chickens through breeding and rearing for the past 8+ years, and I can apply my cell biology and genetics knowledge to such a topic.

I thank you for taking the time to read my blog on this widely debated topic, as alway I value your opinion so please feedback to me.

thanks Andrew


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