The Price of Survival: Yaks’ Adaptation to High Altitudes

The yak ( Bos grunniens ) serves as an exceptional model for studying high-altitude adaptation mechanisms due to its evolutionary success in the hypoxic environment of the Qinghai-Tibet Plateau. While previous research has largely focused on genetic and physiological traits of yaks, the interactions between rumen microbiota and host physiology under hypoxic conditions remain poorly understood. As the largest digestive organ in ruminants, the rumen and its microbiota play a central role in digestion and host nutrition. In this study, a comparative analysis of digestive metabolism and rumen microbiota was carried out in yaks and cattle under varying atmospheric oxygen levels. Our findings reveal that yaks have developed unique microbial strategies to cope with energy deficits in hypoxic stress. These include a shift in rumen microbiota toward amino acid degradation and enhanced long-chain fatty acid biosynthesis, thereby improving energy acquisition despite reduced nutritional intake. However, this metabolic adaptation comes at a physiological cost - reduced microbial crude protein (MCP) synthesis leads to elevated ruminal NH ₃ -N levels, and increased fatty acid metabolism and urea cycle activity contribute to hepatic stress. This study presents the first evidence of metabolic trade-offs in high-altitude adaptation, demonstrating that yaks optimize microbial-mediated energy production at the expense of liver health. These insights deepen our understanding of host-microbiome coevolution mechanisms in extreme environments and highlight biological costs associated with adaptation.