# Comparative Histopathological and Morphometric Analysis of Lung Tissues in Stillborn Cubs of South China Tiger and Amur Tiger

## TL;DR

This study compares lung tissues of stillborn tiger cubs to understand why inbreeding in South China Tigers leads to high cub mortality.

## Contribution

The study identifies hypoxia and inbreeding-related lung abnormalities as key factors in cub mortality among South China Tigers.

## Key findings

- Hypoxia is a significant factor contributing to the mortality of South China Tiger cubs.
- Inbreeding depression may cause abnormal lung development in South China Tiger cubs.
- Lung tissue thickening and pathological changes were observed in stillborn South China Tiger cubs.

## Abstract

The South China Tiger (Panthera tigris amoyensis) is classified as a nationally protected species under the highest conservation category. As this tiger is functionally extinct in the wild, only captive populations remain. Prolonged captivity has led to inbreeding, resulting in severe challenges from inbreeding depression. The reduced reproductive fitness in adults and the mortality rate of young tigers will seriously restrict the sustainable development of the population. To elucidate the underlying causes of elevated cub mortality, this study conducted comparative histopathological and morphometric analyses of lung tissues from stillborn South China Tiger and Amur Tiger (P. t. altaica) cubs. The findings provide crucial scientific insights into the survival challenges confronting endangered species and offer valuable theoretical support for genetic management strategies for the South China Tiger.

This study aimed to determine whether the fetuses experienced hypoxic distress or intra-partum death due to compromised oxygen supply by quantitatively analyzing the lung structures of deceased captive South China Tiger (Panthera tigris amoyensis, SCT) cubs. Furthermore, it investigated the etiology and mechanisms of asphyxia in the deceased cubs and explored potential factors contributing to the high mortality rate of SCT cubs. The research focused on three deceased SCT cubs, using three deceased neonatal Amur Tigers (P. t. altaica, AT) with no inbreeding background as controls. Histological analysis of the cubs’ lungs was conducted using hematoxylin–eosin (H&E) and special staining techniques. The possible causes of death in SCT cubs were evaluated by comparing pulmonary pathological changes and morphological parameters, including alveolar space (P(ASP)) values, mean alveolar linear intercept (Lm), and mean thickness of alveolar septa (Tas). Our research reveals that hypoxia is one of the most significant factors contributing to the mortality of tiger cubs. Additionally, we hypothesize that inbreeding depression may lead to abnormal lung development (e.g., thickening of lung tissue) in SCT cubs. This study lays the foundation for comprehensive investigations into the mortality of highly inbred SCT cubs.