Big Quail Eggs: What's Normal, What's Not, and When to Worry

A customer emailed me a photo last week: a Coturnix egg sitting next to its flock-mates' eggs, looking like it belonged to a different bird. Her question was simple: is this normal, and should I be worried about my hen? Short answer: usually it's normal, sometimes it's a warning sign. Here's how I think about it after years of collecting eggs every morning.

What "normal" egg size looks like by breed

Start by putting a number on it. Eyeballing doesn't tell you much. A digital egg scale that reads in grams will.

• Standard Coturnix (Japanese quail): Michigan State University Extension puts a Coturnix egg at roughly 10 grams (0.4 oz), about 8 percent of the hen's body weight. The same bulletin notes that each hen tends to lay eggs with her own characteristic color pattern, shape and size, so some variation across a flock is expected.
• Jumbo and heavy Coturnix lines: Bigger birds lay bigger eggs. In an 11-generation selection study, a line bred for high body weight laid eggs averaging 14.14 g, compared with 11.43 g in the unselected control line and 9.23 g in a line bred for low body weight.
• Bobwhite: Bobwhites are bigger birds than Coturnix, but MSU notes that Coturnix actually produce the larger eggs. Bobwhites also start laying much later: around 16 weeks versus as early as 6 weeks for Coturnix.
• Button quail (Chinese painted quail): These tiny birds weigh only 28 to 40 g as adults, and their eggs are around 5 g and about 24.5 by 19 mm. Animal Diversity Web notes those eggs are "rather large considering the size of the female."

So if you have jumbos, a 14 g egg is not a freak. If you have a standard Coturnix hen that suddenly lays one well above her usual weight, that's worth paying attention to.

Why some hens lay huge or double-yolk eggs

New layers

The biggest cause of oddball eggs is a hen that has just started laying. A hen's reproductive system takes a while to settle into a rhythm. A review of double-yolked eggs explains that up to 25% of follicles develop in pairs early in the laying period, before the hen's hormones fully stabilize. Two yolks can then release together and end up in one shell. Most of that research is in chickens, but the same paper notes that double yolks show up in domestic poultry and game birds alike. Hendrix Genetics, a laying-hen breeder, puts it plainly: in young birds coming into production, ovulation can be irregular until the follicle order is established, and the occasional hen of any age will lose that control now and then.

Age

Egg size isn't fixed for life, but it doesn't climb forever either. Poultry researchers treat it as a general rule that egg weight usually increases as females age. Yet that same Japanese quail study found egg weights were similar at 15, 23 and 31 weeks, and the authors say feed and environment probably muddy the age effect. In plain terms: most of the change happens as a pullet settles in. If an adult hen in steady lay suddenly throws a giant, age alone probably isn't the reason.

Genetics and jumbo lines

Egg size is heritable. Selecting for heavy body weight drives egg weight up, but the extra size has a cost. In the long-term study above, selection for high body weight reduced egg production by 13.5%. The double-yolk review also notes that the tendency to lay double yolks is relatively heritable compared with other egg defects. Some hens and some lines just do it more.

Nutrition and body condition

Feed matters. The double-yolk research links age, bird type, rearing system and nutrition to how often these eggs appear. In my experience, a well-fed, heavy hen on a rich ration is more likely to throw an occasional giant. That's not a reason to cut her feed. It's a reason to make sure the ration is a proper layer feed, not a pile of treats.

When a big egg becomes a health problem

A big egg on its own is a curiosity. The trouble starts when the hen can't pass it easily. The Merck Veterinary Manual lists "production of overly large or improperly positioned eggs" as one cause of egg binding, where the egg gets stuck inside the bird. Other causes it lists:

• Calcium deficiency. Calcium is needed to build the shell, and hens that lay many eggs back to back can run short. Merck's professional edition notes that calcium deficiency, which results in misshapen or soft-shelled eggs, is often a factor.
• Obesity and inactivity. Merck notes egg binding is most common in overweight, inactive birds.
• Vitamin A deficiency, oviduct disease, genetics and an unsuitable environment.
• First-time layers. Merck lists being a first-time layer as a risk factor. That's the same group that lays the most double yolks.

Prolapse is the other worry. That's when tissue from the vent pushes outside the body. Merck describes cloacal prolapse as a reproductive problem in birds that does better when it's caught and treated early. A hen straining to pass an oversized egg is exactly the bird I keep an eye on.

Merck's guidance is written mostly for pet birds like cockatiels, not quail, but the anatomy and the basic problem are the same. These are general points, not a diagnosis.

Signs to watch for

From Merck's list of egg-binding symptoms, plus what I watch for in my own pens:

• Sitting hunched on the floor, weak or low energy, eyes closed
• Straining, or a tail that bobs with each breath (labored breathing)
• Bloody droppings
• A swollen belly
• A hen who suddenly stops laying
• Any pink or red tissue showing at the vent
• A run of soft-shelled, thin-shelled or misshapen eggs

 

If she's bright, eating, and just laid a whopper? Weigh it, write it down, and keep an eye on her. One giant egg from a young hen is usually just a young hen figuring things out. Repeated giants, shell problems, or a hen that looks off is when you get a professional involved.

My practical takeaways

• Weigh eggs instead of guessing. Know what each breed and each hen normally lays.
• Expect odd eggs in the first weeks of lay. Expect eggs to change size as pullets mature.
• Feed a complete layer ration and keep hens at a healthy weight.
• Soft shells plus a straining hen means it's time to call the vet.

Questions about your birds? Come see our flock at the Bridgewater, NJ showroom (by appointment). We're NPIP certified, #22-456. I'm always happy to look at a weird egg.

— Christian Graninger

Sources

• Michigan State University Extension, The Japanese Quail (Bulletin E-1069)
• Animal Diversity Web (University of Michigan), Coturnix chinensis
• Effects of selection for body weight and egg production on egg quality traits in Japanese quails Kafkas Universitesi Veteriner Fakultesi Dergisi (PDF)
• Effects of mass selection on egg production on some reproductive traits in Japanese quail, European Poultry Science (doi:10.1399/eps.2017.168)
• Nowaczewski et al., Effect of age of Japanese quail on physical and biochemical characteristics of eggs, South African Journal of Animal Science (SciELO SA)
• Analysis of the Quality and Chemical Composition of Double-Yolked Eggs, Animals (PMC11171307)
• Hendrix Genetics, Double yolk eggs
• Merck Veterinary Manual, Reproductive Disorders of Pet Birds (owner edition) and Reproductive Diseases of Pet Birds (professional edition)