PI: G. Bubenik, R.G. White, J. E. Blake, J. E. Rowell and D. Schams

Supporting Agencies: National Sciences and Engineering Research Council, Canada

Five adult bulls, five barren and four pregnant reindeer (Rangifer tarandus) cows, kept outdoors at the Institute of Arctic Biology, University of Alaska Fairbanks were fed ad libitum and sampled from the jugular vein every three weeks for 13 months. Seasonal profiles of plasma hormones were later determined by RIAs. Despite the ad libitum food supply, T3 levels were maintained high (above 2ng/ml) in all 3 groups between Apr and Aug and kept low (around 1 ng/ml) between Sept and Jan. IGF-1 levels peaked in November in males (1000 ng/ml) and peaked in females between Sept-Oct (550-750 ng/ml). The male reproductive axis was activated sequentially: LH levels peaked in May (2 ng/ml), FSH in Jun (53 ng/ml) and testosterone in Sept (19 ng/ml). Peak levels of all three reproductive hormones appear to correlate with the social rank of the individual bull. LH levels in females reached a maximum at the end of August; two smaller peaks, six weeks apart, were also registered in the non-pregnant group. FSH in the pregnant group varied little throughout the year. In non-pregnant cows, after the first peak at the end of August, two subsequent elevations, six weeks apart (each one substantially higher than the previous one) were also observed. It appears that the cows, if not impregnated, are capable of experiencing at least three subsequent estrous cycles. Surprisingly, seasonal levels of testosterone in female reindeer do not correlate with any part of their antler cycle. Therefore it appears that the antler cycle of female reindeer is not directly regulated by their plasma levels of testosterone. Prolactin (PRL) levels in all three groups correlated with photoperiodicity; maxima (139 ng/ml in cows, and 92 ng/ml in bulls) were registered in Jun. Almost non-detectable PRL levels were found between Oct-Mar. PRL levels in lactating cows increased only slightly earlier than in the non-pregnant cows; peak levels were equal in both female groups. Overall peak levels of PRL were maintained for a longer period of time in reindeer than in the white-tailed deer. Seasonal levels of alkaline phosphatase parallel the intensity of antler growth and the progress of the antler cycle (Fig. 5). Peak in males (171.3 IU/ml) was achieved at the end of May; in non-pregnant (94.6 IU/ml) and pregnant females (75.3 IU/ml) peak levels were observed in Jun-Jul. Seasonal levels of cortisol, estrogen, progesterone and STH levels will be reported later.

2. The effect of cyproterone acetate (CA) on antler casting

A significant decline in testosterone is responsible for antler casting in all deer species studied to date. In these species CA, a potent androgen blocker, will cause antler casting within three - four weeks of administration. It was hypothesized that the endocrine regulation of antler casting in reindeer is also dependent on a significant drop in testosterone as it is in other cervids. Two trials were undertaken, both using the same seven yearling reindeer (two males, two females in the treatment group; two males, one female in the control group). In the first trial (November 1992) the animals, all having polished antlers, were given 150mg CA as weekly IM injections for five weeks. Antler casting did not occur. This could have been due to a) incomplete ossification of the pedicle at the beginning of CA treatment b) insufficient dose of CA to effectively block androgens c) the null hypothesis - a sharp drop in testosterone alone does not immediately precipitate antler casting in reindeer. Antler ossification was confirmed by removing one antler from each animal and the second five-week trial, initiated in January, used a higher dose of CA (100 mg/twice weekly). All animals retained their remaining antler at the end of the trial indicating that testosterone alone is not the only important factor in yearling reindeer antler casting. Weekly blood samples were collected during both trials and are currently being analyzed for steroid and protein hormones