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.

中文翻译：

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驯鹿公牛中的醋酸甲羟孕酮：睾丸组织学、大脑中的 cfos 活性、育种成功和精液质量

先前的一项研究报告称，400 毫克剂量的醋酸甲羟孕酮 (MPA) 可减少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，我们在两个单独的试验中重复了该协议。2017 年，从处理后 30 天和 60 天安乐死的 MPA 和对照 (CTL) 驯鹿公牛身上采集的组织和血液样本被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从 8 月到 9 月都有下降趋势，但精子生成指数仍然很高。到 9 月，与 CTL 公牛相比，MPA 中的精子密度较低 (P = 0.05)，两组的精子发生指数均有所下降。八月 CTL 公牛的雄烯二酮 (A4) 浓度最高 (P = 0. 009) 和睾酮 (T) (P = 0.08)，而这些雄激素是 Aug MPA 公牛的基线。到 9 月，CTL 多头中的 A4 和 T 水平下降到 MPA 多头中测量的水平。与 CTL 公牛相比，MPA 中中央杏仁核中 Cfos 活性的 cfos 阳性神经元数量更多 (P = 0.02)，这表明 MPA 公牛中的恐惧反应增强。在第二项试验（2019 年）中，在 7 月至 9 月将它们放入单独后宫的关键点对 MPA 处理的公牛（有（E，n = 4）和没有（IE，n = 4）繁殖经验）进行血液采样与发情同步的奶牛。在 MPA 处理前，E 公牛的 T 浓度最高 (P < 0.001)，但处理后 1 个月，所有八只驯鹿的 T 和 A4 均为基线。在 MPA 处理后 60 天通过电射精收集的精液显示，使用新鲜和冷冻/解冻精液的 E 和 IE 公牛在精子异常方面只有微小差异。只有三头公牛（2 头 E 和 1 头 IE）生育后代。育种成功与以前的育种经验、体重或公牛年龄无关。一些 MPA 公牛繁殖失败似乎是一种行为限制，而不是生理限制。MPA 的有限应用显然是管理非繁殖驯鹿车辙攻击的有用工具。然而，应该研究使用约束和轻度镇静而不是全身麻醉从 MPA 处理的公牛身上收集精液的可能性。这可以提高精液采集的质量，同时增强处理人员和动物的安全。