A Bit Different Anatomy Physiology Roosters

Rooster Fertility Issues

What's Got Your Boys' Mojo?

Just like humans, roosters reach their sexual peak when they are young and then it’s all downhill from there. Men are in their prime between the ages of twenty and thirty; roosters hit their stride between 30-40 weeks and their fertility rates start to decline shortly after their first birthday.

My rooster, Simon, is almost three. He’s never been aggressive with the hens; in fact, I’m often surprised when chicks hatch because I don’t see a lot of mating going on. When other folks complain that their rooster’s favourite hen is missing feathers, my hens look pristine.

For the last several years I’ve sold hatching eggs. In 2018 the hatch rates were quite high, while last year they weren’t as successful. Hatching can be influenced by a number of factors: temperature and humidity fluctuations during incubation, weak stock and both hen and rooster health issues.

This year a couple of people have done test hatches for me. Taking into account incubation issues the fertility rate was @65%. That got me to thinking about the things that might influence rooster fertility, which of course, led to a Google search since it’s not an area I’m familiar with. So if you’re interested in what affects your boys’ mojo this post is for you.

(If you’re not aware of the logistics of how chicken reproduction happens take a look at this post and if you want the inside scoop on rooster genitalia read here.)

They say it takes two to tango and fertility is definitely impacted by both rooster and hen. A mature egg yolk leaves the hen’s ovary and within twenty minutes it’s captured by the infundibulum. The egg yolk is surrounded by the perivitalline membrane (PVM) which holds the germinal disc (GD), where fertilization takes place. The sperm bind to the PVM, make a hole and tunnel into the GD. This is where the sperm fuses with the germinal disc and embryonic development begins.

It takes only one sperm to fertilize an egg, but to ensure a 95% chance that fertilization will happen then about thirty sperm must enter the egg near the germinal disc. There is a small window of opportunity for sperm to to do their job because the yolk leaves the infundibulum (fertilized or not) fifteen minutes later on its descent into the uterus.

So what are the factors that have an impact on rooster fertility?

Exposure To Estrogen Mimickers

Both wild and domestic birds can be exposed to numerous environmental pollutants (agricultural pesticides and insecticides, plastics, etc.) in soil and freshwater.  Many chemicals are considered endocrine (hormone) disruptors because they have the potential to change estrogen-dependent developmental processes and adult physiological functions. Estrogen is often thought of as a female hormone, when in fact it is found in both sexes.

Rooster reproductive systems are regulated, in part, by estrogen with receptors in their efferent ducts and epididymis. Their reproductive systems are a target for estrogen mimickers in both embryos and adults.

In lab tests, male embryos exposed to estrogen during incubation were shown to have anomalies of the comb, significantly decreased semen production and changes in testicular structure and function in adulthood.

Estrogen affected roosters had more cloacal defects such as outgrowths, deformations or a small phallic groove – all conditions that influence fertility.

Bigger Is Not Better

In many bird species, males have eye-catching plumage that serves to advertise what they have on offer and to attract females. Some studies have linked bright colouration with better fertility and sperm performance, but feathers take months to grow and may not always be an accurate indicator of a bird’s current health status.

Testing has been done on roosters, a species where comb characteristics fluctuate on a short-term basis when influenced by environmental and physiological conditions. In the case of chickens, combs might be a better advertisement of a rooster’s health than plumage. The relationship of comb size and color with sperm quality and viability resulted in an interesting finding. It turns out that colour is paramount and bigger is not better. The roosters with the smallest, reddest combs had the highest percentage of viable sperm. Hens that are influenced by a rooster with the biggest comb are actually choosing the rooster with lower fertility. So if you are out rooster shopping remember that the show off may be all talk and no action.

There is also a link between rose comb genetics and poor sperm motility.


I read of one study that found a correlation between roosters who had been vaccinated for Infectious Bronchitis and the development of large numbers of stones in their reproductive system. 75% of the roosters vaccinated with either the live or killed virus developed stones, whereas none of the unvaccinated birds did. Dietary calcium was ruled out as the cause, but there was no definitive understanding about how vaccines might impact the blood-testis-barrier, which is essential for the production of normal, healthy sperm.


Most of us are unaware, or undervalue, the role that stress plays in avian health. There are numerous studies that have found a connection between environmental stress and fertility issues in roosters including:

  • The maximum potential for a rooster’s sperm production occurs when they are in the developmental stage between the ages of 8-10 weeks.
  • Low body weight, heat stress and dehydration in 6-8 week old cockerels can lead to the shut down of testicular function.
  • Temperatures above 32c/90f affect both semen quality and quantity
  • Competition with other roosters (a ratio of less than one rooster per ten hens).
  • Obesity plays a role in both roosters (lower sperm count) and hens (less efficient in transporting sperm to the infundibulum).
  • Lactobacillus is a healthy part of a microbial community that can help to prevent yeast infections and Salmonella. However, there is a link between the presence of lactobacillus in the reproduction tracts of hens or roosters and negative impacts on sperm.

I was curious about what remedies might be offered to boost fertility rates in roosters. I scoured the literature thinking that there would be loads of strategies used by commercial hatcheries to ensure high hatch rates. I found very little, except a mention about the use of herbs (no specifics) and one study that found giving roosters vitamin E (22mg/kg. bodyweight daily) enhanced both sperm count and viability.

If anyone has other information about the impacts on rooster fertility or how to enhance it feel free to contact me.

Credits: Illinois ACES Animal Sciences; Oxford Academic, Biology of Reproduction; NCBI; Poultry World and ResearchGate.

Featured Artwork: Ursulav

2 comments on “Rooster Fertility Issues

  1. Thank you very much. We have had two failed hatches in our incubator this spring and really questioned the cause, considering fertility might be the issue with our little Icelandic guy. He’s full of bravado and very protective, was a hatchery chick himself, but so far no luck. Beautiful plumage and a huge comb; oops. Might be time to think about that!


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