Excal lamb/kid feeding bottles come in 2 different types.
The lamb feeder has a lightweight 1 litre bottle and an air inlet via a small valve in the handle cavity (main picture). This can be covered to slow up the drinking rate if required.
The lamb/kid feeder has a heavier duty feeding teat but also includes an air inlet to control milk flow. For the teat to work correctly the single slit must be vertical.