Medroxyprogesterone acetate in reindeer bulls: testes histology, cfos activity in the brain, breeding success, and semen quality.

A previous study reported that a 400-mg dose of medroxyprogesterone acetate (MPA) reduced male reindeer aggression and blocked development of secondary sexual characteristics but did not completely impair fertility. Here we have repeated that protocol in two separate trials. In 2017, tissues and blood samples, collected from MPA and control (CTL) reindeer bulls, euthanized at 30 and 60 d post-treatment were used to evaluate testes histology and morphometrics, cfos activity in the brain and androgen levels. While testes weight tended to decline from August to September in both groups, indices of spermatogenesis remained high. By September, indices of spermatogenesis were declining in both groups with sperm density lower (P = 0.05) in MPA compared to CTL bulls. Aug CTL bulls had the highest concentrations of androstenedione (A4) (P = 0.009) and testosterone (T) (P = 0.08), whereas these androgens were baseline in Aug MPA bulls. By September, A4 and T levels in CTL bulls declined to levels measured in MPA bulls. Cfos activity had a greater number (P = 0.02) of cfos positive neurons in the central amygdala in MPA compared to CTL bulls, suggesting a heightened fear response among the MPA bulls. In the second trial (2019), MPA-treated bulls, with (E, n = 4) and without (IE, n = 4) breeding experience, were blood sampled at key points from July through September when they were put in individual harems with estrous-synchronized cows. Concentrations of T were greatest (P < 0.001) among E bulls prior to MPA treatment but 1 mo after treatment, both T and A4 were baseline in all eight reindeer. Semen collected by electroejaculation at 60 d post-MPA treatment revealed only minor differences in sperm abnormalities between E and IE bulls using both fresh and frozen/thawed semen. Only three bulls (2 E and 1 IE) sired offspring. Breeding success was not related to previous breeding experience, body weight, or bull age. The failure of some MPA bulls to breed appears to be a behavioral, not a physiological, limitation. Limited application of MPA is clearly a useful tool for managing rut-aggression in non-breeding reindeer. However, the possibility that semen could be collected from MPA-treated bulls using restraint and mild sedation rather than general anesthesia should be investigated. This could improve the quality of semen collection while enhancing the safety of both handlers and animals.

A single 400 mg dose of MPA given to reindeer bulls just before the onset of rut eliminates aggressive behavior and suppresses androgen concentrations without dramatic differences in the gross or histological structure of the testes within the first 30 d of treatment. By 60 d post-treatment, there is evidence of smaller testes size and decreased sperm density in treated bulls. However, if given the opportunity, some treated bulls can still successfully breed. Breeding success in MPA bulls was not solely related to previous breeding experience, body weight, or bull age. Androgen concentrations and semen characteristics did not vary with previous breeding experience. Failure of some treated bulls to breed appears to be a behavioral limitation. Differences in brain activity between control and treated bulls were few except for increased cfos activity in the central amygdala of MPA bulls, potentially increasing the fear response in these reindeer.

Fecal glucocorticoid metabolites reflect hypothalamic-pituitary-adrenal axis activity in muskoxen (Ovibos moschatus).

Muskoxen (Ovibos moschatus), a taxonomically unique Arctic species, are increasingly exposed to climate and other anthropogenic changes. It is critical to develop and validate reliable tools to monitor their physiological stress response in order to assess the impacts of these changes. Here, we measured fecal glucocorticoid metabolite (FGM) levels in response to the administration of adrenocorticotropic hormone (ACTH) in the winter (1 IU/kg) and summer (2 IU/kg) using two enzyme immunoassays, one targeting primarily cortisol and the other targeting primarily corticosterone. Fecal cortisol levels varied substantially within and among individuals, and none of the animals in either challenge showed an increase in fecal cortisol following the injection of ACTH. By contrast, two of six (winter) and two of five (summer) muskoxen showed a clear response in fecal corticosterone levels (i.e., maximal percentage increase as compared to time 0 levels > 100%). Increases in fecal corticosterone post-ACTH injection occurred earlier and were of shorter duration in the summer than in the winter and fecal corticosterone levels were, in general, lower during the summer. These seasonal differences in FGM responses may be related to the use of different individuals (i.e., influence of sex, age, social status, etc.) and to seasonal variations in the metabolism and excretion of glucocorticoids, intestinal transit time, voluntary food intake, and fecal output and moisture content. Results from this study support using FGMs as a biomarker of hypothalamic-pituitary-adrenal axis activity in muskoxen, advance our understanding of the physiological adaptations of mammals living in highly seasonal and extreme environments such as the Arctic, and emphasize the importance of considering seasonality in other species when interpreting FGM levels.

Muskox status, recent variation, and uncertain future.

Muskoxen (Ovibos moschatus) are an integral component of Arctic biodiversity. Given low genetic diversity, their ability to respond to future and rapid Arctic change is unknown, although paleontological history demonstrates adaptability within limits. We discuss status and limitations of current monitoring, and summarize circumpolar status and recent variations, delineating all 55 endemic or translocated populations. Acknowledging uncertainties, global abundance is ca 170 000 muskoxen. Not all populations are thriving. Six populations are in decline, and as recently as the turn of the century, one of these was the largest population in the world, equaling ca 41% of today's total abundance. Climate, diseases, and anthropogenic changes are likely the principal drivers of muskox population change and result in multiple stressors that vary temporally and spatially. Impacts to muskoxen are precipitated by habitat loss/degradation, altered vegetation and species associations, pollution, and harvest. Which elements are relevant for a specific population will vary, as will their cumulative interactions. Our summaries highlight the importance of harmonizing existing data, intensifying long-term monitoring efforts including demographics and health assessments, standardizing and implementing monitoring protocols, and increasing stakeholder engagement/contributions.

The effects of short-term medroxyprogesterone acetate on rut related behaviors, semen characteristics and fertility in farmed reindeer bulls.

The effects of medroxyprogesterone acetate (MPA) on velvet antler cleaning, hypophagia, aggressive behavior and fertility were evaluated in farmed reindeer bulls during a 2-year study. Eight reindeer bulls aged 1-4 years were divided into 2 groups balanced for age. During each year, one group (MPA, n = 4) was treated with MPA 2 wk prior to the expected onset of rut while the other group (CTL, n = 4) served as untreated controls. Feed consumption, behavior and antler cleaning were recorded daily or 3 x weekly for 3 mo. Each year a dominant CTL and MPA bull were put into separate harems of estrous synchronized females for 1 wk in mid-September. Following harem breakup, semen was collected from all bulls via electroejaculation and evaluated. In Year 2 the bulls were switched such that year 1 MPA bulls received the CTL treatment and year 1 CTL bulls received MPA treatment. In Year 2 all eight bulls received MPA treatment/booster following semen collection. In both years, MPA treatment reduced rut associated body weight loss (p ≤ 0.05), rut associated hypophagia (p ≤ 0.001), interfered with velvet antler cleaning, and abolished aggressive rut related behavior. All of these changes suggest suppression of testosterone mediated effects. Alternatively, semen parameters differed little between treatment groups with the exception of reduced sperm concentration and total sperm production in MPA bulls (p ≤ 0.05). All CTL bulls in Year 2 exhibited full rut behavior with the dominant bull successfully breeding 100% of females available for breeding, suggesting no carryover effect of MPA treatment from the previous year. The MPA bull successfully bred 4 of 6 females (Year 1) but the MPA bull in Year 2 failed to sire any offspring. A single 400 mg treatment of MPA just prior to rut was sufficient to suppress rut associated aggression and hypophagia on a short-term (3 mo) basis. It did not however, completely suppress fertility.