Steroid hormone secretion during the ovulatory cycle and pregnancy in farmed Alaskan reindeer1

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-17beta, estrone, and estrone sulfate. Elevated P4 in 80% of the reindeer at the onset of the study indicated that ovarian activity had been initiated. The median date for the onset of the first recorded full-length ovulatory cycle was September 23. In nonbred reindeer, the mean ovulatory cycle length from September to May was 24 +/- 1 d (range 18 to 29 d). Nonbred females continued to cycle throughout the winter, displaying 6 to 8 ovulatory cycles after the beginning of blood sampling. Cycle length (mean 22 to 24 d) 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 in 2 females, whereas the remaining 3 females formed apparently persistent corpora lutea. 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 after 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 and rising coincidently as P4 declined just before parturition. There was a 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 +/- 2.2 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.

Fecal hormones as a non‐invasive population monitoring method for reindeer

“…Blood is the traditional medium for examining hormones that can provide information on female reproductive status (via progesterone [P4] or estradiol; Ropstad et al 2005, Shipka et al 2007), stress levels (via cortisol; Denicola and Swihart 1997, Li et al 2007), and mating and aggressive behavior in males (via testosterone; Whitehead and McEwan 1973, Li et al 2004). Physical manipulation of animals has been shown to directly modify the concentrations of these sex hormones by increasing stress levels (Wesson et al 1979, Barja et al 2008, Togashi et al 2009).…”

“…Progesterone held the most promise for our study as we collected the feces during winter when other sex hormones such as testosterone and oestrogen are at base levels or are fluctuating (Bubenik et al 1997, Shipka et al 2007). We had four main objectives: 1) to validate the extraction and assay procedures for fecal progesterone metabolites in reindeer; 2) to determine if fecal progesterone metabolites reflect the total hormone levels found in plasma; 3) to explore the possibility of identifying female reproductive status (pregnant or not pregnant), sex, and age class (calf, yearling and adult) of reindeer through fecal P4; and 4) to test whether fecal P4 levels differed between the semi‐domesticated and wild reindeer populations.…”

Antler casting in relation to parturition in semi-domesticated female reindeer

“…Estradiol stimulates the growth and mineralization of the antler bone and the cleaning of the velvet (Lincoln & Tyler, 1999). Whether estradiol also suppresses the casting of the hard antlers as suggested by Lincoln & Tyler (1999) is uncertain as Shipka et al (2007) report estradiol at baseline concentrations until approximately 24 week of gestation and rising coincidently as progesteron declined just before parturition. Although uncertainty as to the detailed control mechanism the steroids apparently act to synchronize the antler cycle to the seasonal reproductive cycle with the hard antlers functioning as weapons and social signal both in intra-sexual and inter-sexual competition in winter and in spring (Lincoln & Tyler, 1994).…”

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“…White-tailed deer (Odocoileus virginianus) is a species of great ecological and socioeconomic importance in Mexico (Clemente et al, 2015). That is why aspects like productivity and hormonal levels have to be studied for a better management of the species (Shipka et al, 2007), both for its conservation or exploitation (Pelletier et al, 2003). Hormones regulate individuals' physiology and behavior, as well as their growth, body condition, social behavior, and above all, reproduction (Morden et al, 2011).…”