Do you have a case history posted for your boy? If so, would you please include the link to it. If not, would you please fill one out on our sister list ECHistory7. This gives us much-needed info to be able to answer your questions more completely.
The extra urination can be a sign of uncontrolled PPID (Cushings) and/or IR. Was your boy tested for IR as well as PPID? Is he on pergolide? An ACTH of 57.9 in a known PPID horse is too high and indicates lack of control of the disease.
Does he have salt added to his feed as well as the salt block? How much salt is he consuming from the block? Is this a white salt block or? Is his hay analyzed with the minerals balanced to the analysis? Unless he is consuming a 1-2lb white block per day the salt licking isn't dangerous if he has water access 24/7. Any other type of salt block is not recommended at all. The excessive salt licking could be from boredom if he is spending more time confined in his stall than he was previously used to. Good that he has a slow hay feeder in his stall - does his hay last most of the day or is he finishing it and having long periods with nothing to do? Would not recommend a Likit as they are basically a block of glucose (sugar) for the horse to consume and would be dangerous for an IR horse.
Sorry, more questions than answers for you right now.
Lavinia, Dante, George Too and Peanut
Jan 05, RI
EC Support Team