The Rurtec �Chin-Mark� harness is used to monitor oestrus or mating activity in cattle. The harness is typically applied to a neutered bull, or to an oestrus-active cow, to leave easily identifiable indication of cows oestrus period. Crayons clip into a holder under the chin. The crayons come in three �temperate zone� types - cold, mild, and hot, ideal for ram marking, but for cattle, zones mild and hot are quite adequate. (Mild crayons used in a hot climate may ablate too quickly.) The harness is easily attached and removed with two quick-clips. Crayons can be changed with harness attached, as long as the head is restrained.