I've made what I call "back door" rugs out of denim. Some of my denim is stained (ie manure/grease stains), these I cut into squares and make a rug like one would make a rag quilt, but 2 layers of denim. To avoid intersecting seams, stagger the rows starting with a rectangle unit. Number of squares needed depends on how big the squares are and how big the rug is to be. A 3 x 5 foot one works great on my mud room floor. This time of year the snit melts on the rug not my floor. Then I throw the dirty rug into the washer with DH's dirty jeans. I have to watch these though as they have been known to dry off a newborn calf, grace a wet tractor seat, etc!
We also use cloth towels to clean cows teats before milking. Old sweatshirts, t-shirts, and sox work great for this task and last through many washings of hot water and bleach!