My two overweight mares wear grazing muzzles. Their intake of grass is limited, which is a good thing for their weight, as both teeter on obesity. Yet, I was wondering if this decreased intake affects saliva production, and potentially gastric health. Any thoughts?
Saliva is released in response to chewing, the physical movement of the jaws. Decreased access to pasture or other forages is a risk factor for gastric ulcer formation. As long as your mares have access to a feedstuff that gives them a reason to chew, such as hay, enough saliva should be reaching the stomach to keep ulcers at bay.
Some researchers believe that saliva is released into the mouth when horses press their lips against an object. If this is true, saliva would be discharged from the salivary glands each time a horse bumps its grazing muzzle on the ground to grasp a bite.
The horse you might have to worry about is the one that is frustrated by the muzzle and spends inordinate amounts of time trying to get it off.