my dogs have been urinating a lot

Question
I have two dogs, a silky terrier and a yorkie/silky mix who since today have been urinating a lot. Both were fed half a can of spam with vitamins today for the first time since the dry food ran out. They've drank the same amount of water as usual but for some reason have urinated in big puddles. They are weewee pad trained and in a matter of 2 to 3 hours the pad has been completely full. Could you please explain to me what is going on and if its i should be concerned with? Thank you.

Answer
The spam probably contains a high salt content which means more salt must be removed from the blood by the kidneys and this has the effect of causing more water to also be excreted because the high salt content cause the water to diffuse into the urine and therefore a higher volume of urine to be produced.
I would advise to return them to their normal food asap and if you cant get hold of it for a day or so to feed chicken and rice (proportionally much more rice than chicken - cooked without salt) which is easily digestible and is recommended for dogs with a suspected urinary or digestive problem.
If the problem persists or you notice them drinking a lot more than usual consult a vet as there are various conditions which can cause this which require drug treatment.  I find it unlikely that it is due to anything other than the sudden change in diet though as both dogs have developed the problem simultaneously.
Hope this helps
Sarah