Candling Eggs

Guineafowl eggs are so thick and unusual that an unclear reading after five days of incubation is not a cause for concern.

After five days in the incubator, it's about time we scanned the turkey, guineafowl and peacock eggs to find out what is going on inside the shells. It's easy to scan eggs with a candling torch, and with a little bit of practice, you quickly learn what to look for when the light makes the inside of the egg glow up. We recently scannedpheasant eggs after four days and saw clear signs of progress and development in all of the fertile eggs. A distinct dark blob seemed to sit at the centre of a complicated network of blood vessels inside the shell, and during the course of several days, these blood vessels expanded. 

While candling eggs reveals the progress of the embryos in all its fascinating complexity, it also shows whicheggs are infertile and which are doomed to be nothing more than smelly timebombs.

With high hopes, we began to scan the turkey and guineafowl eggs, peering through the shells in the hope ofspotting telltale signs of life. One of the most immediate and obvious things we noticed when candling the eggswas that there is huge variation between different eggs, not only between the species but also betweenindividuals.

The faint mottling on the turkey eggs was different on every single egg we looked at, and some shells were far thicker than others. Sometimes, the mottling was so irregular that it was impossible to tell if there was anything inside the eggs, and so out of a possible half dozen turkey eggs we scanned, we could only be sure of progress with one. Scanning eggs on day five can give you an idea of what might happen in the future, but it's not a reliable way of "counting your chickens", and we hope to have a few more chicks when they hatch at the beginning of August.

The guineafowl eggs were even more extravagantly marked than the turkey eggs, and we were worried to see a number of cracks in their shells. Living as they do in the dusty, arid regions of sub-saharan Africa, guineafowl lay eggs with shells that are hard and rough, and this is possibly to reduce the risk of water loss on a hot day in the bush. Run your thumb over a guineafowl egg and you'll feel an almost porous surface which you can imagine would soak up rainfall or dew like blotting paper. Guineafowl eggs are really unusual, and they are also known to be very brittle and thick, so it could be that the cracks are less a sign of damage and more an indication that all is well.

When we came to scan the cracked peacock egg, we saw no signs of progress whatsoever. The candling torchshowed how some mud and dirt had got caught under the edge of the crack, which may prove to be fatal for theembryo's development. However, there is still a chance that it could start to develop over the next few days, and after such a short time in the incubator, it would be silly to give up on it now. We'll scan it again in a few days, when progress (or a lack of it) in all the eggs will be more obvious.

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