Looks like I caused some confusion about corn/plant proteins, and urinary
ph.  Corn and plant based protein contains amino acids that the ferret
can use, but the problem with corn and most plant based protein is simple.
When the protein is metabolized it will make the urinary ph alkaline.  When
the protein from meat based protein is metabolized it will make the urinary
ph acidic.  When the urinary ph is alkaline (i.e., plant based protein)
struvite crystals form and urinary problems (crystals, infections, bladder
stones, blockages, etc) happen.  Why does this happen?  Corn and most
cereal grains have low levels of the essential amino acid methionine.
Meat based protein has a lot of methionine.  When the essential amino acid
methionine is metabolized it produces a sulfate (SO4-2) that is excreted in
the urine as sulfuric acid (H2SO4), which acidifies the urine!  The good
news is most cat and ferret foods have dl-methionine as an ingredient.
This is added to acidify the urine.  That is why we do not commonly see
urinary problems in ferrets.
 
Thus corn as a carbohydrate source will not cause urinary problems.
 
Jerry Murray, DVM
[Posted in FML issue 3397]