About the windows in the barn. The windows provide natural light to the poultry house or pigsty. Their area must be at least 1/10 of the floor area. If the room is intended for fattening, then the area of windows can be reduced by half (up to 0.4 square meters).
The windows should be protected with metal mesh or wooden slats from the indoor of the barn so that birds or animals do not break the window glass and are not injured, and intruders do not get inside. As for the glass, the usual window glass does not transmit ultraviolet light. Therefore, if possible, you should arrange an outdoor ground run for farm animals or poultry or install windows with uviol glass.