Is Broodiness Contagious?

What, exactly, causes a chicken to go broody is a subject that baffles even the best poultry scientists. One thing we know is that whether or not a hen decides to brood depends on three interconnecting factors: genetics, hormones, and environment. So let’s look at these three factors, and maybe we’ll find an answer to the question, “Is broodiness contagious?”

Broody Genetics

The genetics of broodiness is of great interest to researchers who seek to eliminate the broodiness trait. Why? Because broody hens temporarily stop laying eggs.

So people who keep chickens primarily for eggs persistently cull broody hens. As a result, breeds best known for superior laying ability are the least apt to brood. In particular, the selective breeding of white Leghorns (along with a few other breeds and strains) has led to an almost complete loss of parental behavior.

Despite the fact that most common chicken breeds express the broodiness trait, it actually has low heritability. But just as it has been bred out of certain breeds and strains, it may be increased in future generations by keeping birds resulting from a natural hatch.

Scientists don’t yet know exactly which genes control broodiness. But clearly broodiness relies on at least two dominant autosomal genes. Most likely one gene causes broodiness, and another inhibits the behavior, with equal influence.

Chicken breeds that are best known as reliable broodies include Australorp, Aseel, Cochin, Dorking, Jersey Giant, Modern and Old English Games, buff Orpington, and Sumatra. Chanteclers and Fayoumis, among others, rarely brood within their first year of lay. But they may brood successfully during subsequent laying cycles.

Broody Hormones

Broodiness is induced by the synergistic action of the hormones estrogen and progesterone. This syngergy triggers the pituitary to release high concentrations of the hormone prolactin.

Also involved in broodiness is an increase in the hormone corticosterone. Meanwhile, the hormones testosterone and triiodothyronine decrease.

In order for prolactin to induce a hen to set, she must be in lay and genetically capable of broody behavior. Breeds that brood possess the genes encoding prolactin and other hormones that control broody behavior, but non-broody breeds do not.

Environmental Signals

Not only must a hen be genetically able, and in laying condition, she also must receive environmental signals that encourage broodiness. Increasing day length during springtime is one such signal.

Another is the availability of a quiet, undisturbed, dimly lit nest site. An accumulation of eggs is yet another trigger. But not all hens need that particular signal to induce setting. I once had a hen that wanted to hatch a single avocado pit she retrieved from our compost pile.

An additional environmental signal that triggers broodiness is the presence of other brooding hens. So, is broodiness contagious? Well, once genetics and hormones line up, and the environmental conditions are right, then yes. I suppose you might conclude that broodiness is indeed contagious.