Relationship between Age and Tooth Cementum Layers in Norwegian Reindeer

Abstract

A rapid freeze-sectioning technique for demonstrating annuli in tooth cementurn of rein- deer (Rangifer tarandus) is described. The technique has been applied to a reference material of 37 adult known-age animals and to 1,100 jawbones from two reindeer populations. The known-age ma- terial strongly indicates that the annulation is referable to age. The presence of special rut lines in teeth of males from high quality range indicates that rut-line formation might be related to condition. During a 5-year survey (1963-67) of populations of wild reindeer in mountain areas in southern Norway, some 1,100 lower jawbones from hunted animals were col- lected for age determination. This large sample made it necessary to work out a fairly rapid aging procedure. During the preliminary work several methods were at- tempted. All of these were based on the findings that annuli laid down in tooth den- tine or cementum can be used to determine age in different mammalian species (Laws 1952, 1953, Sergeant and Pimlott 1959, Low and Cowan 1963, McEwan 1963, Linhart and Knowlton 1967, and others). We did not succeed in revealing the an- nuli by grinding, and embedding pro- cedures required too much time. However, annuli can also be demonstrated in decalci- fied frozen sections, as mentioned by Mc- Ewan (1963:112). Although apparently not in use by other authors, freeze-section- ing seemed promising, being both rapid and simple. We accordingly worked out a procedure, details of which will be pre- sented together with a reliability test per- formed on specimens of known age. We noted early that the presence of special rut lines in teeth from males seemed 1 We wish to thank the Norwegian State Game Research Institute and the University of Oslo for financial support, and the State Veterinary Labora- tory for Northern Norway, Harstad, for the supply of known-age material. to be restricted to one of the two popula- tions studied. We feel that a discussion of this observation might also throw some light on the formation of stainable growth layers in teeth. MATERIAL AND METHODS The reference material consisted of lower jawbones from: 1. Eight males and 11 females (domestic) of known age supplied by the State Vet- erinary Laboratory for Northern Norway. 2. Sixteen males and 2 females tagged as calves and killed at different times of the year in Ottadalen wild reindeer area. This area is populated with a small number of animals in very good condition, and the quality of the range is considered excep- tionally good. 3. Thirty males and 19 females killed during the hunting season (Sept. 1-25) in Dovre wild reindeer area and determined from tooth development to be approxi- mately 16 months old. Compared with Ottadalen, the Dovre area is considered overgrazed, owing to previous overpopula- tion. During the survey period the animals here seemed to be in poor condition. The rest of the material consisted of mandibles from 139 males and 22 females from the Ottadalen area, and from 343 males and 511 females from the Dovre area, all killed during the hunting season.