Is giving saline drenches good for race horses?

YES

Administration of a saline drench before strenuous exercise ensures that body fluid balance, energy production processes and antioxidant protection are all operating at optimum levels so muscle recovery will be as rapid as  possible.

yes  but after  the race  to prevent the metabolique acidose after the efforts

Yes it is good, especially the compounds and sugars such as glucose ... There is a compound called Novacoc contains caffeine

all medicines has different effects to animals, depends of the case. if you re living middle east after hard traning program you can use but if you adding extra things to saline please talk a professional.

yes , prevent dehydration ,prevent metabolic

if horse high temp. reduce temp. with out any medicine