Mine get baths before every show and before every body clipping because they clip 10 times easier after a bath than before because the dirt is gone. I would probably say for the older horses who show pretty much week to week, they get bathed once a week and the ones who are showing lightly or not at all probably get bathed 2 times a month. In the winter they are just little dirt balls though, it is to cold to give baths and all they get is a good brushing. I would say my horses would never mind if winter did not go away just so they would not have to get clean, especially my stallion, he hates to be wet whether it be rain or bath water.
To make sure they do not dry out I use healthy haircare brand hair moisturizer on the entire horse, body and all. This cures the drying out problem and the shampoo I use now does not seem to dry them out even if we do not use the moisturizer on them at all. I use the healthy haircare herbal shampoo and on the grey or light colored horses I use the silverado silver shampoo (like white and bright)and it is made by the same company. If you can not tell I am a Healthy Haircare freak...I should be their spokeswoman. LOL