There has to be familiarity among the sheep for them to readily flock. It takes at least several weeks, and sometimes months, for strange sheep to fully integrate into a normally responding flock. This is extremely important to keep in mind when planning a trial that uses sheep from more than one common source. With experience one can often reasonably predict how sheep will react if breed, age, health, type of terrain, weather conditions and time of day, prior exposure to working dogs and similar information is known. At a trial, the most accurate way of predicting how your draw of sheep will react is to closely watch as many runs as possible prior to yours.
Different breeds react differently to dogs.
Suffolks particularly will often stand their ground and fight, especially if they perceive weakness in a dog. Many of the down breeds are quite intelligent and will quickly learn bad habits on reruns. However, the type of management system the finewools come from can affect their behavior drastically. Fresh range sheep that have had minimal contact with dogs or people can be quite unpredictable in a trial situation. They may run wild, stand and fight, run for awhile and then fight, or any other interesting combination of behaviors.