Recently, I had a call from Mexico regarding a quite rare occurrence. Eggs started being green (slightly so, but definitely greenish!) The owner was alarmed because the eggs were for the fresh market. The attending veterianarian had rulled out any disease problems and it was left to the feed. So, they contacted me!
As it happened, after some questions back and forth, this producer had recently been offered a cheap load of imported cottonseed meal and he had started using it at 5% in all his laying hen formulas (it appears, the 5% rule of thumb is a universal one!) This was not the only ‘alternative’ ingredient added to the formulas at the same time (we are in a global crisis after all) and so it was not obvious what had happened.
Now, cottonseeds contain a yellow pigment called gossypol. There are some varieties without this pigment, but it is generally safe to assume any cottonseed meal will contain gossypol. Concentration varies, but it is about 1% with only 0.1% being free gossypol.
Free gossypol is not that harmful for birds, but even at low concentrations it can cause egg yolk discoloration starting from green, to brown, even to black! This intensifies with intake and egg cold storage. It is fortunate that free gossypol is easily bound by iron and this is the only remedy, indeed. In our case above, we added 1 kg of ferrous sulphate per tonne of feed and things returned back to normal.
Of course, if cottonseed meal contains more than 0.5-1.0% residual oil, eggs will start appearing with a ‘rose’ tinted albumen, but that’s another’s blog story!
Did you ever happen to encounter this problem and what was the story there?