We are raising Longhorn cattle and we have 2 donkeys on the ranch, soon to be 1, as I am getting rid of the jack. I'll explain more on that in a minute.
Last December we lost a calf to what we think were coyotes. Shortly thereafter I picked up a donkey (jenny) from a friend of mine who ranches in South Texas. The donkey had been running with a herd of Charolais when I got it, and was used to cattle.
I hauled the donkey home and put it in the pen for a day or so and then turned it out with the cows. As soon as the cows saw it they started acting crazy, bawling, and trying to run it off. They succeeded to the point that the cows stayed on one end of the place and the donkey on the other. This went on for about a month or 2, until they finally started to accept her a little more. So after all that, I really couldn't say she is doing any good, but she's still out there.
Now to the jack. About a month ago, the owner of the ranch acquired a jack from a neighbor down the road. He turned it in with the jenny, thinking it would be good to get her bred. Well, the jack immediately went to work, against her will I might add. A few weeks ago I noticed one of the young heifers came up and both her back legs were cut up pretty bad. In the back of my mind, I thought it looked like teeth marks, but I figured she had just got cut up in some wire or something. I told the owner my suspicions about the jack and what I had heard about them. He dismissed it, and then last week I told him I had found 3 more head with similiar bite marks, and he either needed to find a home for the jack it, or it needed to be shot. He called the lady he got it from, and I think she has located a home for the jack, but she said they didn't want it until it was gelded. Until then, I have him penned up by himself.
My advice, if you get a donkey, get a jenny - don't get a jack, unless you have him cut. Personally, I don't think the longhorns need much protection. From my experience, the longhorns hate dogs/coyotes worse than the donkeys. Actually the donkeys will run away from my blue heeler, but most of the cattle will go on the attack if the heeler gets too close. She usually takes a wide swath around the cattle when following me thru the pasture, unless I call her to do something.