However, they aren't always the most reliable security beasts.
The dairy next door to our cattle farm had two donkeys to protect their herd of milk cows from coyotes. The owner had to get rid of them after one of them killed several newborn calves.
You can’t use a male or Jack, it has to be female or Jenny. The males can get aggressive with the animals they are supposed to protect, even after they have lived with them a while. A lot of people don’t realize that and are shocked when it happens.