As farming would have it, we have two varieties in South Africa.
The first is the 'good' variety, the "Spineless Prickley Pear" which has good feeding value and produces a large edible fruit which is grown as a 'drought protection' with advantages(fruit)! It is grown commercially in some parts of the country.
The variety you see in my pictures is the 'common' variety which is a weed and only produces cladodes with looooong thorns and small fruit! By the time you have harvested the suitable cladodes, used a gas blowtorch to remove the spines, chopped it, dried it and added molasses to make it palatable, you might as well have trucked in commercial feed!
Two 'bugs' were brought in to try and eradicate it. Cochineal is a very slow acting 'fungus' type white growth which eventually stunts the plant, I don't ever see it killing it! The Cactoblastis worm is a striped worm which goes into the cladodes and eats it from the inside resulting in the plant collapsing!
Both of these 'bugs' seem to affect the 'good' variety more than the 'common' variety!