Corn gluten feed is produced in a somewhat chemical intensive process. Corn is treated to remove/extract the starch and oil for ethanol and corn syrup production. The leftovers are turned into corn gluten feed pellets as a byproduct. It is a very unbalanced feed in that it is higher in sulfur than a cow needs, high in phosphorus, low in calcium with a lot of variation in minerals and vitamins. It is high in protein since the corn protein is still there, but the starch has been removed. So, protein is high as a per cent of the total in the leftovers. Calcium to phosphorus ratio is important in a mineral/nutrition program. CGF has too little calcium for the amount of phosphorus present. This imbalanced nutrition is why you should limit the amount of CGF as a per cent of the total diet unless you mix other things with it (like calcium) and pay attention to the percentages in the final mix. Something to watch if you purchase bulk CGF and mix it yourself. The plants that make the CGF probably put most of their effort on the oil and starch side (ethanol and corn syrup) instead of quality of the byproduct. Dark color CGF is an indication that it was overcooked in the process.
Here is some information on feeding CGF.
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