Dear Bee –
I’ve heard of a lot of folks dealing with egg-bound hens.
Thoughts about what causes this?
In my opinion? Too much fat around the vent area. Too old hens that are ovulating and producing eggs abnormally. Take a look at this diagram and see what a buildup of fat tissue around the vent area would look like and just what it would block and pinch in the way of reproduction. Same thing happens with sheep as they tend to store fat internally instead of underneath the skin. If they gain too much fat around the uterus, they have problems with lambing. It narrows and blocks the area around the cervix and vagina.
When I would butcher a cull Buff Orpingon hen, I'd find a huge amount of fat around the vent area.... more so than any other bird I'd ever butchered ~ even more than meaty breeds. These birds were never good layers and would have problems such as thin shells, no shells, soft shells, and irregular laying patterns (abnormal ovulation). As many folks know, this happens in women who are overweight as well.... abnormal ovulation, excessive bleeding, ovarian cysts.
(Right from the outset you can see the problems this hen would have had laying an egg... she had thick fat layers completely around her vent area, bottom and top.)
I've never had what I considered an egg bound hen ~ probably because I cull them for certain traits. But with the rise in city and backyard flocks you see folks buying BOs and other pet quality chickens that are docile, get very little exercise and eat quite a bit... and then this is compounded by people feeding "treats" such as cooked rice, cooked anything, wild bird seed, BOSS (black oil sunflower seeds), etc. as a daily ration.
They are also keeping these birds past the age of regular laying and into the age where they are starting to have irregular ovulation. This leads to trouble in normal egg production...all the parts are wearing out, misfiring, etc. They don't cull as soon as these problems arise and pretty soon they have a hen that is egg bound due to ovarian cysts, internal laying, peritonitis from broken shells, etc.
When excess fat develops around the cloaca, you will see it completely around the cloaca, not just underneath it. This fat is pressing against where the eggs need to come into the cloaca.
So that "begs the question"... How do you keep hens from getting fat? I was of the mind that a good, healthy bird would eat only what they needed. We talk about putting out enough that they finish it and learning from that what amount to put out. If they will overeat, how can we regulate that?
Or... is it just certain breeds that have that issue?
Certain breeds are more prone to it. You can also make sure they get adequate exercise with free ranging in electric netting paddocks. You can make them work for their feed by foraging and then only feed them in the evening, feed them portions instead of free choice and feed them a normal percentage of protein and fats in their diets. Treat laden diets and chickens that only get to get out of the run in the evening to walk around the yard are going to be just like kids that eat a lot of snacks and only do exercise in gym class.
A good healthy bird is, also, often an opportunistic eater, so if their only opportunity for activity in a coop and run is to walk around the run, dust a little in the corner, lay an egg or eat, which do you think they will do the most of? They will eat, as it fulfills their need to forage, hunt and peck.
You can regulate that by watching your birds and seeing which hen is the first at feeder each day and if she is still there when that last of the feeder is being cleaned up - this is a bird that is not very feed thrifty. Most birds will eat their fill and go back out to forage or groom.... a few hoggy breeds or birds in the flock are still browsing the feeder. Watch those birds.
You can find out a lot about your birds if you watch them with intent... not just with pleasure at their antics but with an eye towards their feed habits, their activity levels, their interaction within the flock, their social abilities in regards to flocking, foraging, evading predators, etc.
All of these things are taken into account when I determine who to cull from my flock... not just laying, health and disposition. I want to shape my flock for harmony, hardiness, economy and laying efficacy. In other words, a flock that requires very little input from me to survive, thrive and fulfill their purpose.