We'll see what Aine has to say, but I always figured that "snuffy" referred to the snort/snuffle cattle make when they are just milling around, so firey and snuffy would mean ready to hit the trail, or stampede especially if the "dogies" (motherless calves) were restless and upset. Unhappy babies tend to make unhappy grown ups. Keep the babies quiet, and you keep everybody else quiet.