# Regulatory Mechanisms and Safety Evaluation of Exogenous Progesterone for Suppression of Rutting Behavior in Male Sika Deer (Cervus nippon)

## TL;DR

Injecting progesterone in male sika deer reduces aggressive rutting behavior without harming their health or antler growth.

## Contribution

A safe and effective hormonal strategy using exogenous progesterone to suppress rutting behavior in sika deer is proposed.

## Key findings

- Progesterone significantly reduced aggression and mating activity in male sika deer.
- The treatment suppressed reproductive hormones and altered metabolism without adverse health effects.
- Antler performance and organ health were not negatively impacted by the progesterone treatment.

## Abstract

Aggression among adult male sika deer during the rutting season causes injuries, fatalities, and economic losses in high-density farming, posing significant animal welfare challenges. We assessed whether a single injection of long-acting progesterone could safely and effectively suppress these behaviors. Twelve deer were randomly assigned to a treatment group (one 330 mg subcutaneous progesterone injection) or a control group. Over a 60-day period, we monitored behavior, serum hormones and metabolites, health markers, and later antler performance. The treatment significantly reduced aggression and mating activity, linked to suppressed reproductive hormones and altered metabolism. Importantly, it had no adverse effects on organ health or antler yield. This study presents a practical hormonal strategy to improve welfare and sustainability in deer production by mitigating rutting-related aggression.

Managing rutting aggression is critical in sika deer (Cervus nippon) farming. To mitigate rutting aggression in male sika deer, this study evaluated the efficacy, safety, and physiological mechanisms of exogenous progesterone. Twelve sika deer were randomly assigned to either a control group or a treatment group, with behavior monitored for 60 days post-administration. Serum hormones, non-targeted serum metabolomics, biochemical indicators (including reflecting liver and kidney function), and subsequent antler performance were assessed. The treatment group exhibited significantly reduced aggressive and mating behavior throughout the study (p < 0.05). HPG axis hormones (GnRH, LH, FSH, and T) and PRL were significantly reduced throughout the study (p < 0.05), while TRH was elevated, T4 declined, and GH showed time-dependent fluctuations. Differential metabolites were significantly enriched in pathways related to nucleotide metabolism, pyruvate metabolism, and arachidonic acid metabolism. Except for a transient decrease in the ALB/GLB ratio (p < 0.05), no significant changes were observed in other biochemical indicators or antler performance (p > 0.05). This study confirms that exogenous progesterone effectively controls rutting behavior primarily via HPG-axis suppression and multi-system endocrine interactions, without inducing detectable organ toxicity or compromising production, supporting its use as a safe management intervention.