Institute of Agriculture, Natural Resources and Extension, University of Alaska Fairbanks, Fairbanks, AK 99775, USA.
Animal Resources Center, University of Alaska Fairbanks, Fairbanks, AK 99775, USA.
J Anim Sci. 2022 Jun 1;100(6). doi: 10.1093/jas/skac106.
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.
先前的一项研究报告称，400 毫克剂量的醋酸甲羟孕酮（MPA）可降低雄性驯鹿的攻击性并阻止第二性征的发育，但不会完全损害生育能力。在这里，我们在两项独立的试验中重复了该方案。2017 年，从 MPA 和对照（CTL）驯鹿公牛在治疗后 30 天和 60 天安乐死时采集的组织和血液样本用于评估睾丸组织学和形态计量学、大脑中的 cfos 活性和雄激素水平。虽然两组的睾丸重量都有从 8 月到 9 月下降的趋势，但精子发生指数仍然很高。到 9 月，两组的精子发生指数都在下降，MPA 组的精子密度较低（P=0.05）。8 月 CTL 公牛的雄烯二酮（A4）（P=0.009）和睾酮（T）（P=0.08）浓度最高，而 8 月 MPA 公牛的这些雄激素处于基线水平。到 9 月，CTL 公牛的 A4 和 T 水平下降到 MPA 公牛的测量水平。与 CTL 公牛相比，MPA 公牛的中央杏仁核中的 cfos 阳性神经元数量更多（P=0.02），表明 MPA 公牛的恐惧反应更为强烈。在第二项试验（2019 年）中，接受 MPA 治疗的公牛（E，n=4）和未接受治疗的公牛（IE，n=4）在 7 月至 9 月期间有配种经验，当时他们被放入发情同步的母牛的单独畜群中。在接受 MPA 治疗之前，E 公牛的 T 浓度最高（P<0.001），但治疗后 1 个月，所有 8 只驯鹿的 T 和 A4 均处于基线水平。电刺激采精 60 天后，用新鲜和冷冻/解冻精液对 E 和 IE 公牛的精子异常进行分析，发现两者之间只有很小的差异。只有三头公牛（2 头 E 公牛和 1 头 IE 公牛）使母畜受孕。繁殖成功与之前的繁殖经验、体重或公牛年龄无关。一些 MPA 公牛无法繁殖似乎是一种行为限制，而不是生理限制。有限地应用 MPA 显然是管理非繁殖驯鹿发情期攻击性的有用工具。然而，应该研究是否可以通过约束和轻度镇静而不是全身麻醉从接受 MPA 治疗的公牛中采集精液。这可以提高精液采集的质量，同时提高处理人员和动物的安全性。
