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

Authors: ROWELL, JANICE - University Of Alaska; BLAKE, JOHN - University Of Alaska; ROTH, KATIE - University Of Nebraska; SUTTON, COURTNEY - University Of Nebraska; SACHSE, COLLEEN - University Of Nebraska; CUPP, ANDREA - University Of Nebraska; Geary, Thomas; Zezeski, Abby; ALEXANDER, BRENDA - University Of Wyoming; ZIEGLER, ROBERT - University Of Wyoming; SHIPKA, MILAN - Retired Non ARS Employee

Submitted to: Journal of Animal Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/29/2022
Publication Date: 6/1/2022
Citation: Rowell, J.E., Blake, J.E., Roth, K., Sutton, C., Sachse, C., Cupp, A.S., Geary, T.W., Zezeski, A.L., Alexander, B.M., Ziegler, R.L., Shipka, M.P. 2022. Medroxyprogesterone acetate in reindeer bulls: testes histology, cfos activity in the brain, breeding success and semen quality. Journal of Animal Sciences. 100(6):1-11. https://doi.org/10.1093/jas/skac106.
DOI: https://doi.org/10.1093/jas/skac106

Interpretive Summary: A single, long-acting dose of MPA (man-made progestin) given to reindeer bulls just before the onset of rut, eliminates aggressive behavior. MPA also decreased androgen production without major effects on testes function within the first 30 days of treatment. By 60 days post-treatment testes size was smaller and function decreased in MPA bulls. However, if given the opportunity, some MPA bulls can still successfully breed. Breeding success in MPA bulls was not dependent on previous breeding experience. Previous breeding experience of MPA bulls did not affect androgen production or semen fertility measures much. Differences in brain activity suggest possible increased fear response in MPA reindeer.

Technical Abstract: NA 400 mg dose of medroxyprogesterone acetate (MPA) reduced male reindeer aggression and blocked development of secondary sexual characteristics but did not completely impair fertility. In 2017, tissues and blood samples, collected from MPA and control (CTL) reindeer bulls, euthanized at 30 and 60 d post-treatment (n=2 MPA bulls; n=2 CTL at each sampling date) were used to evaluate testes histology and morphometrics, cfos activity in the brain and androgen levels. There was a tendency for combined testes weight (P = 0.08), left testis length (P = 0.09) and diameter (P = 0.11) to decline from Aug to Sept and to be lower (P = 0.02) in MPA compared to CTL bulls. Indices of spermatogenesis did not differ between MPA and CTL in Aug (P > 0.10). By Sept the percentage of tubules with mature sperm was decreased (P = 0.04) for both MPA and CTL bulls. Sperm density was greater in Aug MPA bulls (P = 0.03), and CTL bulls (P = 0.05) vs Sept MPA bulls. Aug CTL bulls had the greatest concentrations of A4 (P = 0.009) and T (P = 0.08) whereas both these hormones were baseline in MPA bulls. In Sept, A4 and T concentrations in CTL bulls had declined, similar to levels seen in Sept MPA bulls. Cfos activity, evaluated in multiple areas of the brain, had a greater number (P = 0.02) of cfos positive neurons in the central amygdala in MPA bulls compared to CTL bulls. In 2019, MPA treated bulls with breeding experience (E, n=4) and without breeding experience (IE, n=4) were put in individual harems with 3-4 estrous-synchronized cows. Three bulls (2 E and 1 IE) sired one calf each. Concentrations of androstenedione (A4) did not differ (P = 0.30) between E and IE bulls, although testosterone (T) concentrations were greater (P < 0.001) among E bulls prior to MPA injection than all IE bulls and E bulls post-treatment. One month after MPA injection, both T and A4 were baseline in all reindeer. Semen collected by electroejaculation at 60 days post MPA revealed only minor differences in sperm abnormalities between E and IE (greater head defects [P = 0.04] and tendency for greater DAG defect [P = 0.10]) bulls. Flow cytometry measures of frozen/thawed semen from the same ejaculates revealed greater (P = 0.02) percentage of sperm with polarized mitochondria (energy potential) and a tendency (P = 0.08) for greater percentage of live sperm with strong antioxidant capacity in E bulls. Fluctuating T and A4 levels in September may indicate a waning of MPA effects.