Steroid hormone secretion during the ovulatory cycle and pregnancy in farmed Alaskan reindeer

¹ Department of Plant, Animal and Soil Sciences, School of Natural Resources and Agricultural Sciences, University of Alaska Fairbanks, Fairbanks, AK 99775; Center for Reproductive Biology, Washington State University, Pullman, WA 99164
² Department of Plant, Animal and Soil Sciences, School of Natural Resources and Agricultural Sciences, University of Alaska Fairbanks, Fairbanks, AK 99775
³ Department of Plant, Animal and Soil Sciences, School of Natural Resources and Agricultural Sciences, University of Alaska Fairbanks, Fairbanks, AK 99775; Department of Allied Health, Tanana Valley Campus, University of Alaska Fairbanks, Fairbanks, AK 99775

^* To whom correspondence should be addressed. E-mail: ffmps{at}uaf.edu.

	Abstract

Seasonal endocrine changes in 5 non-bred and 10 pregnant Alaskan reindeer have been documented. Blood samples were collected from early September until early May, spanning the breeding season, gestation or the anovulatory period. Plasma was analyzed by RIA for progesterone (P₄), estradiol-17, estrone, and estrone sulfate. Elevated P₄ in 80% of the reindeer at the onset of the study indicated that ovarian activity had been initiated. Median date for the onset of the first recorded full length ovulatory cycle was September 23. In non-bred reindeer, mean ovulatory cycle length from September to May was 24 ± 1 d (range 18 to 29 d). Non-bred females continued to cycle over the winter, displaying 6 to 8 ovulatory cycles after the beginning of blood sampling. Cycle length did not vary between individuals (P = 0.170) or over the course of the winter (P = 0.244). In early April, ovulatory cycles ceased with normal demise of the corpus luteum (CL) in 2 females, while the remaining 3 females formed apparent, persistent CL. Natural service breeding occurred between September 10 and October 2 and P₄ profiles indicated that all breeding females conceived to the first mating. Concentrations of P₄ rose steadily following conception and remained elevated throughout gestation, with mean concentrations not varying significantly (P = 0.104) from 4 to 28 wk of gestation. Estrogens all followed patterns similar to each other, remaining at baseline concentrations until approximately 24 wk of gestation, rising coincidently as P₄ declined just before parturition. There was continual overlap throughout the winter in peak P₄ concentrations observed in cycling and pregnant reindeer. Calving occurred between April 8 and May 2, resulting in a mean gestation length of 211 ± 2.24 d (range: 198 to 221 d). Information from this study can be used by Alaskan reindeer producers to improve management and profitability of reindeer production.

Key Words: Estrogens, Gestation length, Ovulatory cycle, Pregnancy, Progesterone, Reindeer