Cat food has very high protein designed to digest within the very short intestinal maze peculiar to cats. Some cat foods are better than others. I might mix it with their regular feed (swine feed) but I wouldn't feed it to pigs by itself. As for it having ants (insects in general)however (or if it was moldy) it doesn't sound like it should be fed to anything. You never want your diet to cause problems. A diet should provide the nutritional markers to promote healthy growth and maintenance. The word "free" (not meant as an address to Noel but in consideration of the original question) should not be given any more weight in a decsion than the word "appropriate." On a side note I have lately been reading about cheap ways to feed pigs. IMO, it doesn't get much cheaper than $13.00 for 100 pounds of food designed specifically for swine. The economy of alternatives sometimes has a double edge in terms of growth and health and labor. If I had access to fresh fruits, vegetables, and grains, and was able to combine them to meet the nutritionl needs of my pigs in a more economical way, I certainly would. I've read about other feeds that sound like they are meeting nutritional needs so I know it is just swine food that does it. But it is very easy to scoop out 2.5 pounds of swine feed and pour in their bowls each morning and evening and know they are in peak condition for breeding or butchering. Just .02 cents worth.