Regardless of whether we keep chickens to make a bit of extra money or primarily as pets, most of us are pleased when our hens are laying regularly. Although consistently large eggs might be the goal for some small flock keepers there is often a disconnect as to the price our birds pay to meet our expectations.
Domesticated chickens were derived from Red Jungle Fowl, a wild bird from Southeast Asia and China. Over a period of eight thousand years they spread across the globe and have been selectively bred for size, plumage, egg shell colour, and a variety of features like crests, muffs, silkied or frizzled feathers, dark skin or five toes. Most importantly, many breeds have evolved to lay larger and many more eggs than wild birds. Their ancestors, like most bird species, laid one or two clutches totaling up to 20 eggs a year. Modern commercially farmed hens such as Leghorns or hybrids can now lay up to 320 eggs a year. For them, egg production is a full-time job and a tough one at that.
There are a number of factors that impact egg production – daylight, molting, broodiness, weather or stress – but the primary ones are genetics and diet. There can be individual differences between birds, but generally breed determines both egg size and the number of eggs a hen lays. The size of egg a hen lays is also influenced by her anatomy: the size of the shell gland and ratio of the length of the magnum (where albumen is deposited) to the whole length of the oviduct; and her overall body size. The protein level in chick Starter feed in their first 10 weeks is the main factor influencing skeletal size of any particular breed of hen. Hens with bigger and longer bones tend to become larger birds with the capacity to lay bigger eggs.
It seem that extra large eggs aren’t enough, you can now buy double yolked eggs in the supermarket:
My flock consists of a number of hens descended from heritage breeds, none of them prolific layers. In fact some of them, like my six frizzled hens, would not make the cut by some producer’s standards. The gene that creates their curled feathers is also linked to lower egg production. My goal has never been to push my girls and I don’t see them as egg machines.
A quick Google search reveals far more posts about how to increase production or egg size than a concern as to how egg laying actually affects the health of our birds. Lots of us are aware that commercially raised hens start to lay at a young egg, lay large eggs often (i.e. almost daily) and are considered ‘spent’ by 16- 18 months when they are shipped off to make pet food. I’ve only ever had one production layer: I rescued her from the side of the road and integrated her into my flock. Compared to most of my hens that laid medium to large eggs two or three times a week, with breaks spread throughout the year, Ruby laid large or extra large eggs almost every day. I understand from a purely economic basis why folks buy high production birds, but there are consequences to pushing hens beyond their natural capacity.
Impacts On High Producing And/Or Large Egg Laying Hens
- Egg Binding: Large eggs can be difficult to pass which can be painful, cause tears in the reproductive tract or lead to egg binding. I’ve only once had to deal with egg binding: Mango had taken a break to incubate eggs and raise her chicks. After a hiatus of almost three months she started laying again and one egg actually got stuck in her vent. After consulting my vet I ended up breaking the shell and extricating the contents without issue. The problem was the egg stretched her vent so it lost muscle control and became permanently distended, which meant Mango dribbled poop all the time. After several months, I ended up euthanizing her when she seemed to be going downhill. A vent that doesn’t close properly is at risk for bacteria to enter the oviduct leading to infection, and poop caked to feathers can be an attractant for fly strike.
- Prolapsed Vent: When a hen attempts to lay a too-large egg or is new to laying the internal parts of the reproductive tract can be pushed out of the body. While it can be fixed, in many cases, a severe prolapse can lead to death. Unfortunately I have had to euthanize two young hens who suffered major prolapses associated with laying their first few eggs.
- Salpingitis: The pelvic muscles associated with frequent laying or passing large eggs can get ‘loose’ allowing fecal material to enter the reproductive tract causing a bacterial infection salpingitis (lash egg).
- Ovarian Cancer and other reproductive tract tumours are common in domestic hens, especially in high egg producing breeds. Up to 35% of hens develop ovarian cancer by the time they are 2½ years old (Poultry DVM). I lost two hens last year that were confirmed by necropsy to have had ovarian cancer.
- Osteoporosis: Egg shells are made of calcium which hens draw from reserves in their leg bones. Constant laying, coupled with inadequate sources of dietary calcium, can lead to the loss of bone calcium, weakened legs, stress fractures and osteoporosis.
- Keel Bone Fractures: The growth of a laying hen’s skeletal frame ceases around sexual maturity (approximately 18 weeks of age), but the bone formation process of the keel (breast bone) continues for another five months. When young hens begin producing eggs, the tip of the keel is made of cartilage and not bone. In high-producing layers their keel bone receives inadequate calcium for proper bone growth during the early laying period. A study from the University of Copenhagen revealed that the majority of commercial Danish layers suffer from keel bone fractures, which are the result of disproportionately large eggs that put internal stress on a hen’s skeletal system.
“Selectively breeding hens for high productivity, whether larger eggs or larger numbers of eggs, can cause a range of problems such as osteoporosis, bone breakage and prolapse. We need to breed and feed hens so that they can produce eggs without risk to their health or welfare.” – Phil Brooke, Compassion In World Farming.
Managing Risk Factors Associated With Egg Production
Regardless of the reasons why we keep chickens it’s important to understand the negative health impacts that egg laying can have on our birds and shift our attitudes from seeing our non-laying hens or lower production birds as ‘slackers’, ‘free loaders’ and ‘not earning their keep’ to accepting our role in selectively breeding for traits that may cause hens to experience illness and premature death.
- The use of artificial lighting influences egg size by accelerating or delaying the age at which hens start to lay eggs. The younger a hen is when she starts to lay, the smaller her eggs will be for the first year. The start of egg production can be delayed by providing less than 10 hours of light/day until 19 weeks of age.
- Hens need a natural seasonal break and opportunities to slow down in laying. I’ve never used lighting to force my birds to lay more or to lay year round.
- Protein levels in manufactured feed can influence egg size at different stages of production. In the first two months of laying, feeding 18% – 20% protein Layer feed increases egg size. After 36 weeks of age, feeding 15% – 17% protein helps to slow increases in egg size.
- Problems with large sized eggs may also be caused by nutritional imbalances relating to methionine or linoleic acid, or magnesium. Make sure that your flock is on a balanced feed (i.e. correct ratios of calcium, phosphorus and magnesium).
- Obesity can contribute to egg related issues (i.e. double-yolks and large size), egg binding and prolapsed vent. Ensure that your flock isn’t fed too many unhealthy snacks (i.e. those high in sugar, salt and fat) and that treats comprise a small proportion of their overall diet.
- Obtain birds that are not produced for their large sized eggs or high production laying.
- Selectively breed for smaller sized eggs and educate your egg customers on the health impacts extra large eggs have on hens.
The longer I have chickens the more I understand that many of their health issues are due to selective breeding and pushing birds to their limits. By choosing to support practices that enhance animal welfare we will increase the quality, and longevity, of our hens’ lives.
Credits: Frontiers In Veterinary Science; Manitoba Dept. Of Agriculture; My Pet Chicken; RSPCA; Science News.