Requesting info on cat/dog contraceptives

I came across this info in a book called The Whole Kitty Catalogue:

" Millions of very nice cats don't have homes. To reduce their number many countries include cat contraceptives in free food that is left out for feral or abandoned cats to consume. With each bite they receive a small dosage of a hormone that limits their ability to become pregnant -more or less "natural "population control . The alternative-rounding up the cats and euthanizing them- is too unpleasant to think about."

I had read a some years ago about a "major pet food company"( they didn't mention which one) that had come up with the idea of a contraceptive form of pet food that could be given to household pets, and cats/dogs in general. It seems that the veterinary associations rose up "en masse" to stop it, threatening the pet food company with law suits, etc because it threatened the vets' business. THe company pulled the product. I don't think it even got on the market.
For feral colonies it would seem like an ideal solution as actual sterilizations through veterinarians involve trapping /shaving the area /trauma and sometimes not all ferals are caught and sometimes if winter is approaching and a colony had just been discovered there is a delay until Spring which only compounds the situation.
Has anyone heard of what these countries are using as contraceptives for feral cats/dogs? Why haven't countries like Greece taken this solution long before this if something is available? What can be done to get this info, if there is a contraceptive pet food, out to those countries,etc who need that info?

Yes, I have heard of this contraceptive and believe it is being used in the USA. There is a great need for this right here in North America, where the populations of feral cats are out of control, due to human irresponsibility and ignorance.

Trapping, spaying and neutering and releasing feral cats is very labour intensive and expensive,and these contraceptives would certainly make things easier for everyone, especially the cats.

they do that with the bunnies here, and not only contraceptives but some areas use a type of sexually transmitted disease to make them infertile to, it is quite effective with the bunnies, trying to catch and kill them or poision them has so many problems associated. but alas there are still quite a number of bunnies left but the numbers are not plague proportions anymore which is great, but again it has been drought for so long that is yet to be known for sure, get some good rains and the bunies may go wild again if the contraceptions have not worked properly, only time will tell.
my only worry for using it for cats and dogs is the harm a bad person could do with it, what for instance if you had show dogs or similar and a competitor got hold of such a product or even a disgruntled neighbor?? but i suppose that is a risk you take with most dangerous products.

my only worry for using it for cats and dogs is the harm a bad person could do with it, what for instance if you had show dogs or similar and a competitor got hold of such a product or even a disgruntled neighbor??

With over 100,000 homeless dogs listed on Petfinder ALONE (many purebreds), not being able to breed a dog is really not such a bad thing.