Note: This program originally aired August 17, 2013.
Last week’s show, was admittedly, very fun, and I hope you enjoyed it (to listen click here). This week however I want to take a few moments and relay some interesting information I discovered, pertaining to chickens and broodiness, and the poultry community in general.
It turns out that if you do any research on the causes of broodiness (the tendency of a hen to want to sit on a nest and incubate eggs, instead of just visiting the nest to lay a daily egg), two distinct conversations emerge. The first includes the backyard chicken community, those raising a small flock of birds for eggs and pleasure. Their information is purely anecdotal and covers a wide range of observations and advice. The other conversation is from the scientific community, particularly the scientific community working for the poultry industry. The thrust of their research is in preventing broodiness, as it interrupts the hens’ laying, and laying eggs is what it is all about (for that sector of the industry). Every day a hen lives but doesn’t lay an egg is a waste of resources in the eyes of industry. These two perspectives make for interesting reading, as you can imagine.
I am curious about what triggers a hen to go broody, and in asking this question we have to keep in mind a few things. First, chickens are birds, and second they are domesticated and selectively bred. In saying that they are birds, we acknowledge that they retain some physiologic and behavioral traits of wild birds. Their domestication has reduced or altered some of those traits. In the wild birds mate and then lay fertilized eggs, usually a set number, a clutch, and then incubate them. This is generally tied to environmental conditions, particularly day length. Chickens are birds, so yes, they lay eggs. They were domesticated approximately 4000 years ago from a south Asian bird called Red Jungle Fowl. These wild ancestors look a lot like chickens, but have a much more typical reproductive pattern, laying fertilized eggs in clutches a few times a year. In the domestication process however, the relatively rare (in the wild) trait of laying unfertilized eggs has been emphasized over and over again, to the point where domestic chickens can lay an egg nearly every day for a year or more, with the rate of egg laying tapering with age. Hens can lay eggs for their entire lives and never even see a rooster.
If you ask an online backyard chicken keeping forum what causes a chicken to go broody, or better yet, how to make your chicken go broody, you will get a plethora of responses which range from dumb luck, to leaving eggs under the hen, to putting dummy eggs or even golf balls under the hen, to day length and season, to breed. The most common theme seems to be the accumulation of eggs in the nest, which appears to trigger something in the wild bird part of the chickens’ wee little brain, something that says “yes, you have your clutch, now sit on it”. If we think about the implications for chicken neurology, that means that the part of the chicken brain that decides to be broody is separate from the part of the chicken brain that is used for mating; interesting, and based on our evidence, totally anecdotal. If you look in the scientific literature for the cause of poultry broodiness a totally different plot develops. It turns out there isn’t much in the literature about the causes of poultry broodiness, only how to prevent it. And that is because most of the research on chickens is done for the benefit of the poultry industry, either by industry scientists or agricultural extension agencies. These studies describe in detail what happens when a chicken goes broody (brain chemistry changes in ways similar to mammals, the pituitary gland triggers the production of the hormone prolactin, which among other things, inhibits gonadotropin stimulated ovulation, i.e. egg laying), but don’t really examine why chickens exhibit this behavior. It is sort of like the question is mute, chickens are birds, that’s why they go broody, what we need to know is how to stop it. And that is what the studies are all about—tests of what they can inject in or feed to chickens to prevent the surge of prolactin that causes the cessation of egg laying, which is the bottom line for the egg industry.
So I never got my question answered. Science has never looked at the question of why a chicken goes broody or how to make a chicken go broody, because industry has no need for that, they have machines that incubate eggs instead. On this I will throw my lot in with the backyard chicken crew, observing, questioning, testing and doing informal science with the best of them. And not knowing the answer doesn’t really bother me. I actually prefer that some things lay beyond our control, and that mysteries in nature abound. If there were no mysteries, our curiosity would have no food, no medium on which to grow and flourish, and that would be as soul killing as any cement floored mechanized egg producing factory farm. So the next time you crack an egg, pause, and ponder, what you know about that egg, and more importantly, what you don’t know.
References:
Advice from Mother Earth News: http://www.motherearthnews.com/homesteading-and-livestock/encourage-hens-to-hatch-eggs.aspx#axzz2actDPDU
Originally published in Backyard Poultry http://www.themodernhomestead.us/article/broody-hens-1.html
From the USDA (mainly focused on how to prevent broodiness in commercial flocks): http://www.ars.usda.gov/is/ar/archive/nov95/broodiness1195.htm?pf=1
Way , way , way more than you ever wanted to know about prolactin: http://www.sp.uconn.edu/~ttc02001/MCB3210-5210/RA%20%28V%29/PRLR%20Signal%20Transduction%20Pathways.pdf
The original chickens, Red Jungle Fowl: http://www.gbwf.org/pheasants/junglefowl_red.html
A bit about chicken domestication:
http://www.sciencedaily.com/releases/2008/02/080229102059.htm
