Effects of endurance training on skeletal muscle mitochondrial respiration in Siberian huskies and Alaskan huskies

Siberian huskies (SH) and Alaskan huskies (AH), sharing ancestry with ancient sled dogs, were hypothesized to achieve similar skeletal muscle (SM) mitochondrial respiration capacities and densities through endurance training. High-resolution respirometry of SM biopsies from SH and AH during off-season (5 SH, 4 AH) and racing-season (5 SH, 7 AH) revealed a striking increase in mass-specific succinate-linked mitochondrial complex II (CII) activity during racing-season, in both SH (+75%) and AH (+129%). These increases were accompanied by increased protein content in SM for both SH (+37%) and AH (+56%). Elevated CII respiratory capacity can potentially reflect increased fatty acid utilization. NADH-linked complex I (CI) respiration increased significantly only in AH (+35%), which also, unlike SH, exhibited significantly elevated citrate synthase activity (+270%). Both groups showed reduced protein-specific residual oxygen consumption during racing-season (SH: -45%, AH: -48%) and increased reactive oxygen species production. Together, these changes point to more efficient mitochondria with minimized energy loss in raced dogs. A minimally invasive sampling approach was validated, using NSAIDs, local anesthesia, light oral sedation, a micro biopsy gun, and individualized environments to minimize distress. This secured good animal welfare and provided a practical method for field-based or repeated SM biopsies without general anesthesia.