The council made sure that everyone knew that the cows that would be slaughtered were animals, not people-turned-livestock.
But what no one knew, was that the regular cows had already been slaughtered a long time ago.
Cows were always taken away in groups and secretly taken to wizards that used magic to shut down most of their brains,
making them act like ordinary cows, before spreading them among several different farms.
Even many of the farmers believed that they were normal animals and used them as such.
The cows were slaughtered, bred and sold like regular livestock, while the other former citizens simply watched, unaware of the truth.
All of the new products lead to the kingdoms wealth to reach a new high and made them the main supplier of meat,
milk and leather on the entire continent, which gave those that were on the council more influence than ever.
The method that turned the former citizens into 'ordinary' cows was now simply called the 'procedure' and more and more transformed people were subjected to it every day, only stopping when about a quarter of the original population was left.
This was no coincidence; the council had purposefully stopped once they were down to the exact amount needed to maintain the deception, only subjecting more to the 'prodecure' when the amount of intelligent cows crossed a certain number.
The transformed citizens continued having and educating children, unaware of the fact that it may lead to their 'disappearance'.
The reason why the council continued to use the 'procedure' wasn't because they needed more 'normal' cows, as the ones they already had were more than enough to breed and maintain a stable supply with.
It was simply because managing a smaller number of transformees was easier for them.