That sounds like an interesting mod that adds some realism to the animal husbandry process in Farming Simulator 25. This feature where baby animals are sold when the husbandry is full is a nice touch as it prevents the deletion of animals and adds another layer of management for players to consider. It also reflects real-life farming practices where excess animals are often sold or traded.
In your example, with a cowshed having a capacity of 20 cows and currently housing 18 cows, if 4 of those cows are ready to reproduce, upon reproducing, 2 calves will be added to the shed, reaching the maximum capacity of 20 cows. The mod then ensures that the excess 2 calves are sold to maintain the population at the desired level. This mechanic helps players prevent overcrowding in their animal husbandry buildings while generating additional income from selling the surplus animals.
Overall, this mod seems like a great addition to the game, offering players a more realistic and engaging animal husbandry experience while also introducing new strategic elements to manage their livestock effectively. It adds depth to the gameplay and encourages players to make thoughtful decisions about breeding and selling animals to maintain a balanced and profitable farm.