EFFECT OF TESTOSTERONE ON ANTLER GROWTH IN YEARLING MALE REINDEER

1. T h e effect of exogenous tes tosterone o n a n d e r g r o w t h i n y e a r l i n g male re indeer (Rangifer tarandus tarandus) was tested. 2 . T e s t o s t e r o n e (33 m g / k g ) i n h i b i t e d ant ler g r o w t h , a n d i n one a n i m a l i n d u c e d c lean ing a n d s u b s e q u e n t c a s t i n g o f the antlers . T h i s a n i m a l g r e w a n e w set of ant lers , w h i c h w e r e c leaned at the n o r m a l t i m e . 3. D u r i n g t reatment , there w a s an inverse r e l a t i o n s h i p b e t w e e n peak testosterone levels a n d antler g r o w t h rate. 4. T h e r e was n o effect o f t rea tment o n b o d y w e i g h t o r f o o d i n t a k e . 5. It is c o n c l u d e d that the effects o f testosterone o n ant ler g r o w t h are q u a l i t a t i v e l y the same i n r e i n d e e r as i n o t h e r deer. H o w e v e r , because h i g h testosterone doses w e r e necessary to p r o d u c e effects, it is q u e s t i o n a b l e w h e t h e r th is h o r m o n e n o r m a l l y is r e s p o n s i b l e f o r the cessat ion o f ant ler g r o w t h i n re indeer .


INTRODUCTION
The calcification of deer antlers, and the shedding of the velvet, is thought to be controlled by the increasing concentrations of testosterone during late summer and autumn.However, in reindeer it is believed that the antler cycle is not affected by testosterone because both sexes carry antlers, the first set of antlers develop prepubertally, and castrates regularly cast the old antlers and grow a new set every year (Bubenik 1966).However, this view has been challenged by Leader-Williams (1979).He suggested that although there may excist other factors inducing calcification in females and castrates, in the males the effects of these factors are normally overridden by the presence of testosterone.
If this view is correct, exogenous testosterone should retard antler growth, induce calcification of the antler and shedding of the velvet, in reindeer as in other deer.This paper reports the effect of exogenous testosterone on antler growth in yearling male reindeer.

MATERIALS AND METHODS
All animals used in this study were yearling male reindeer from herds of semidomestic reindeer.The animals were kept at the Norwegian State Reindeer Research on Hinnøya (68°25'N).They were kept in individual pens and fed å reindeer feed concentrate (RF 71).The composition of RF 71 is given by Jacobsen and Skjenneberg (1979).Daily food intake was recorded.
In the first experiment, three animals weighing 75 ± 3 kg were given 100 mg testosterone propionate intramuscularly daily for six days starting on 6 June.On the sixth day, each animal also received lg testosterone propionate subcutanously.Thereafter, each animal received 0.5 g testosterone propionate an the 10th and 14th day after the start of the experiment.The hormone was given as a slurry of crystals in physiological saline.Three animals received physiological saline at the same schedule.
In a second experiment, four animals (body weight not recorded) received 500 mg testosterone enantate (Primoteston-Depot, Schering AG) and 100 mg testosterone propionate (Sigma T-1875) intramuscularly on 22 June.Four animals serving as control received sterile olive oil.
The animals were weighed once or twice every month from the end of May to the end of August.
Simultanously, the length of all antler beams and tines were measured, and blood samples were taken by jugular puncture.The blood was allowed to clot, the serum was separated by sentrifugation, and divided into several aliquots that were stored at -20°C until assayed for testosterone, using a 40-1 Significance of differences between groups were tested with a 2-way ANOVA, using p=0.05 as level of significance.

RESULTS
In the first experiment, testosterone levels in the experimental animals rose gradually to peak levels (15 to 37 ng/ml) one week after the last injection.At the next sampling (13 July) testosterone levels were lower in the animals which had previously received testosterone than in the controls (Fig. la).
There was a significant reduction in the rate of antler growth in the testosterone-treated animals (Fig. lb).There was no significant reduction in antler growth rate during the two weeks before the last injection.The animal with highest recorded testosterone levels during treatment (37 ng/ml), cleaned the antlers during the end of July, and lost both antlers on 31 July.Subsequently, it grew a new set of small antlers, which were cleaned during the end of August, at the same time as in the other five animals.
In the second experiment, testosterone levels reached peak values (9.2 to 14.1 ng/ml) in the hormone-treated animals on the first sampling, one week after treatment.Thereafter, the testosterone levels stabilized at 2.1 to 6.4 ng/ml for 2 weeks.In this experiment, the antlers were badly broken in one control and two experimental animals.In one of the two remaining experimental animals, antler growth was extremely rapid before the treatment period, and ceased almost completely after the treatment.In the other, antler growth rate was not overtly different from the control animals.When all results are taken together, there appeared to be an inverse relation between antler growth rate and peak testosterone levels (Fig. 2).
There was no effect of the treatment on food intake or body weight.

DISCUSSION
The results of the first experiment indicate that the effect of testosterone on antler growth are qualititively the same in reindeer as in other species of deer.However, it is questionable whether testosterone normally plays a dominant part in the regulation of antler calcification and cleaning.Judging from the normal range of body weights in other species, the doses (as related to body weight) used in this investigation was probably more than twice those used in sika (Goss 1968), white-tailed (Wislocki et al. 1947), and red deer (Lincoln 1972), and so, reindeer antlers may be less sensitive than those of other deer to the effects of testosterone.This conclusion is also borne out by the relationship between antler growth and testosterone levels (Fig. 2).Although peak testosterone levels as high as 40 to 65 ng/ml have been reported (Whitehead & McEwan 1973, Ryg in press), peak levels are most often in the range 5 to 15 ng/ml (Ringberg Lund-Larsen 1977, Stokkan 1980, Ryg & Jacobsen 1982, Ryg in press), and in this range, testosterone would be expected to have only marginal effects.
In contrast to the effect on one of the animals in the present report, termination of testosterone treatment did not cause antler casting in sika deer (Goss 1963) or red deer (Lincoln et al. 1972).This does not necessarily imply a species difference; the seemingly different results could depend on differences in the doses employed, or on differences in the endogenous testosterone production in the posttreatment period.The immediate onset of new antler growth after casting in July, as compared to the normal lag of 2 to 3 months between casting and regrowth suggests the existence of an antler growth stimulation factor that is present in summer but absent in winter.
Alternatively, there may be an inhibiting factor that is present in winter but absent in summer.
In summary, the effects of testosterone on antler growth are qualitatively much the same in reindeer as in other deer.However, the sensitivity to testosterone is low, and it is doubtful whether testosterone normally is responsible for the inhibition of antler growth in reindeer.The present data, therefore, support the classical view.