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

Authors: ROWELL, JANICE - University Of Alaska; Geary, Thomas; BLAKE, JOHN - University Of Alaska; Zezeski, Abby; SHIPKA, MILAN - University Of Alaska

Submitted to: Theriogenology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2019
Publication Date: 8/27/2019
Publication URL: https://handle.nal.usda.gov/10113/6615396
Citation: Rowell, J.E., Geary, T.W., Blake, J.E., Zezeski, A.L., Shipka, M.P. 2019. The effects of short-term medroxyprogesterone acetate on rut related behaviors, semen characteristics and fertility in farmed reindeer bulls. Theriogenology. 140:201-209. https://doi.org/10.1016/j.theriogenology.2019.08.029.
DOI: https://doi.org/10.1016/j.theriogenology.2019.08.029

Interpretive Summary: In this study we evaluated the effects of a man-made progestin (MPA) for its ability to prevent aggressive behavior in reindeer bulls during the rut. We also wanted to know if it affects bull fertility and feed intake. In a 2-year study, reindeer bulls received either MPA about 2 weeks prior to the beginning of rut or no treatment (untreated controls; CON). Behavior, feed intake and antler cleaning were recorded daily for 3 months. Each year, the dominant bull from both treatments was put into separate harems with reindeer cows for breeding. After harem breakup, semen was collected and evaluated. In Year 2 the bulls received the opposite treatments and the same measurements were recorded. After semen collection in Year 2, all bulls received MPA to prevent additional weight loss. Treatment with MPA reduced weight loss, interfered with velvet antler cleaning and prevented aggressive behavior. Semen production was decreased, but fertility was not affected by MPA treatment. In Year 1, 4 of 6 cows exposed to the MPA bull were pregnant and 5 of 6 cows exposed to the CON bull were pregnant. In Year 2, all of the cows exposed to the CON bull were pregnant but none of the cows exposed to the MPA bull were pregnant. The MPA bull in Year 2 had no prior breeding experience. Treatment with MPA seemed to suppress his desire to breed females that were in heat. A single treatment of MPA just prior to rut was enough to suppress rut associated aggression and prevent drastic weight loss in reindeer bulls during the breeding season. It did not, however, completely suppress fertility. This research is valuable to the reindeer farming industry to prevent injury to owners and improve winter survival of reindeer bulls that lose a tremendous amount of weight during the breeding season.

Technical Abstract: In this study we evaluated the effects of medroxyprogesterone acetate (MPA), a progestin and LH inhibitor, on velvet antler cleaning, hypophagia, aggressive behavior and fertility in farmed reindeer bulls in a 2-year study. Reindeer bulls aged 1-4 y 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 beginning of rut behavior while the other group (CTL n=4) remained untreated controls. Behavior, feed consumption and antler cleaning were recorded daily for 3 mo. The dominant bull from both CTL and MPA each year were put into separate harems for 1 week with estrous synchronized females in mid-September. Following harem breakup, semen was collected via electroejaculation and evaluated. In Year 2 the bulls were switched such that year 1 MPA bulls received CTL treatment and year 1 CTL bulls received MPA treatment. All eight bulls received MPA treatment/booster following semen collection in Year 2. In both years, MPA treatment reduced rut-associated body weight loss (P = 0.05), seasonal hypophagia (P < 0.0?), , interfered with velvet antler cleaning, and abolished aggressive rut-related behavior. All of these metrics indicate suppression of systemic testosterone. Alternatively, semen parameters differed little between treatment groups with the exception of reduced (P = 0.05) sperm concentration and total sperm production in MPA bulls. All CTL bulls in Year 2 exhibited full rut with the dominant bull successfully breeding 100% of females in harem, suggesting no carry over 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.