1,222. When Not to Let an Animal Eat
186:3 If the working animal can't eat because it's thirsty, it must be watered.
186:4 If an animal is working with some food that is unhealthy for it, then it may be muzzled. This is because the Torah only commanded us in the matter so that the animal could enjoy the food it is working. Eating something bad for it would not be considered enjoyment.