The tups have been with the sheep for two weeks. Each day the tups are rudded. This is a colouring applied to the underside of the tup, so as the females are covered, the tup leaves his telltale mark! At the end of each week Chris marks the sheep that have been served, with a paint mark.
This process known as smitting. Each week the smit mark is applied to a different part of the sheep's body. The colour of the smit also tell Chris which tup the sheep is in lamb to. Next April when the sheep are gathered in for lambing we can tell by the smit mark which week they are likely to have their lambs. Complicated isn't it?