Thank you! Now I understand. They haven't reproduced, yet but I will try to trade them, when they do. I also haven't seen how it's put into the trading port, but I hope it will show as soon as there are calves. Can I get rid of the original 4 as well? I have more trading goods, that I need.
A stable seems to be just the right thing for me to build. Since I build the rice field, I swim in grain and don't really know, what to do with all of it. Give some of the oats to the animals, seems to be a good thing. I will try that.