I double their granulated salt intake when big weather changes are forecast. Sport horses here, get 1 Tablespoon of granulated salt daily mixed in the once daily, grain and wet beet pulp. I give them each 2 Tablespoons of the granulated salt once daily, when storms, high or low temp changes are forecast. It “seems” to help increase water comsumption. Buckets are empty to the bottom most days, water is lower than “normal-for-them” as we refill tanks daily.
Ours are used to the daily salt, so getting a bit more does not cause refusal to eat their grain mix. Studies recently have said horses do not usually get enough plain, white salt, so supplementing is often needed. They CANNOT lick enough salt off blocks to provide what their bodies need. They just get tired of licking, maybe tongue gets sore, not because “they know they got enough salt.” Especially true with horses that sweat often during work.
You could pull out their tongue to put salt on it! Worked for me when one horse refused to eat the salt. She and I talked about it the second day of pulling out her tongue and salting it. I told her “You are going to get this salt inside you, the nice way on your grain or on your tongue EVERY DAY!!” She thought it over, cleaned up her salty grain mix the third day and every day after!! No more impaction colics with her again!!
Maybe luck? I prefer to think she understood my threat! Ha ha