Sheep and other animals can not tell you how they feel, until there are very clear behavioral signs, most of the time the animal is then in serious trouble.
This is a link to my post on my other website.
The reason for putting oil in the horse feed was to enhance the shine of their hair coat, as I was showing horses at that time. I do add mineral oil to the feed or by drench to a horse with colic.
Granny
Granny's Homestead 