Bantam egg yolks? As big as normal sized chicken yolks?

There is this idea going around that egg yolks from bantam chickens are the same size as yolks from normal sized chickens (actually, someone on Instagram asked me to find out). I have to say, the first time we cracked our bantam's egg, we thought the yolk looked the same size as our normal laying hens egg. So just to prove this point, I did a bit of literature research. So is it true, bantam yolks are the same size as normal yolks?




I did a bit of a literature search, but nothing came up that suggested that this was the case. In reality, not many science papers were done on this because there was not much commercial value to bantam eggs. There was some research on yolk to egg white ratios in laying chickens. Mainly for the food manufacturing industry, where some places required lots of yolk or lots of whites only.

Since there was not much research available, I resorted to my own experiment.

I measured and compared the yolks from my chickens. This is probably not a great population sample as I only have 1 bantam chicken (Goldilocks, the Pekin chicken) and the rest would be considered normal sized chickens. Eggs were taken from 2 Araucanas and 2 Maran chickens, with the rest of the eggs taken from a sole chicken of that breed. Breeds tested:

Araucana n=6
Australorp n=4
Leghorn n=5
Maran n=6
Pekin n=6

Eggs were weighed on a digital scale with the yolk and the white weighed individually.  Care was taken to remove as much of the egg white as possible from the yolk before weighing. The egg white was weighed with the liquid portion (not just the albumen was weighed).

Here is the result:

Yolk weight across different breeds. Error bars are standard deviation. Asterisk denotes statistical significant difference to the Pekin yolk (p<0.05)

 MYTH: The bantam eggs weighed less than all the yolks of the other breeds, with the Leghorn leading the charge on yolk weight. Error bars are standard deviation from the mean. This shows that was some variation in yolk weight across the different eggs measured.

And, just to make this even better, I did some stats on this, this is a big thing as I really hate stats. Statisticians are awesome, because they can take my crappy data and determine what is significant using equations and regressions I have never heard of. I mean a Tukey test just conjures up an image of Christmas, and I have still no idea when I should be using that test. Anyway, I digress...

I did the only test I know, student t-test, with a null hypothesis that they are all the same. The reference yolk weight was the Pekin's egg. Guess what, all shows (with a p value of <0.05) that the yolk weights are all significant different to the Pekin, EXCEPT the Maran yolk. They could be said to be of a comparable size.


So with the numbers, I also did a ratio of yolk to white.

Ratio of yolk weight to egg white weight. Error bars are standard deviation. Asterisks denotes statistical significant difference to the Pekin ratio

Well, what do you know, Goldilocks eggs have an almost 1:1 ratio of yolk to white. Meaning that she as as much egg white and egg yolk. How interesting is that. Araucana's are also pretty good with this, but the Leghorn fails at this.

Again I did some stats on this. This time, the Pekin ratio of yolk to white was significantly different to all the other chickens.


Interestingly, the Leghorn also laid the heaviest egg, meaning that most of her egg was the white. Don't put too much stock to this, this egg weight included the shell, which depending on thickness, can add a significant amount of weight.

No error bars on this as I didn't have enough range (I only decided to start weighing the whole egg towards the end of the experiment)

It has also been reported that the ratio of yolk to white increases with age, but then decreases again after about 1.8 years of age (97 weeks was the measured age). The Marans, Leghorn and Pekin are al about 1 year old, with the Araucana and Australorp about 2.5 to 3.5 years. So not quite the trend with Araucana eggs! It has also been reported with larger eggs have a lower yolk:white ratio, which is definitely what we saw here.

Another report showed that eggs laid early in the morning weigh heavier than eggs laid in the afternoon. The weight of the egg decreases as the day progresses. It may be because the hen has waited all night to lay the egg and puts an extra bit in the egg?  I have to also say that Spot, our Leghorn is a morning layer. But this may not mean much as she is a breed that is known to lay large eggs.

How interesting is this? My little experiment agrees with (some) published literature!

So what does all of this data tells us (about my chickens)?

- Pekin bantams lay small eggs (well that was obvious)
- Pekin bantams have smaller yolks than the big chickens
-Pekin bantams have less egg white than the big chickens
-If you want the same amount of yolk than white, use Pekin bantam eggs
-If you want large yolks and not too much white, use Araucana eggs
-If you want small yolks and more white, use Maran eggs
-If you want large everything, go for a Leghorn or Australorp
-Heavier eggs generally mean more white than yolk, but according to literature this could be attributed to more water in the white portion

Hope you enjoyed reading this sciencey post and learned something. Remember, I only had one bantam chicken and this may not be the case for all bantams. Plus, my sample size was very small and for some breeds, I only had one laying chicken. So this data can't be extrapolated for all eggs laid by that breed.

Maybe you can try some of your own eggs and let me know. It would be interesting if it correlates with mine!

Cuddle your chickens!

References
Suk, YO & Park, C (2001) Effect of breed and age of hens on the yolk to albumen ratio in two different genetic stocks, Poultry Science, 80:855-858

Ahn, DU; Kim SM & Shu, H (1997) Effect of egg size and strain and age of hens on the solids content of chicken eggs, Poultry Science, 76:914-919