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.