Adipocyte mitochondria in dairy cows reveals constraints in growth and signals adaptive metabolic responses

Understanding the dynamics of metabolic regulation in the body requires an in-depth examination of the distribution and characteristics of mitochondrial populations within adipose tissue. This study aimed to investigate the correlation between mitochondrial size and the expansion of white adipocytes across different Body Condition Scores (BCS) in dairy cows. BCS was used to categorize cows into three groups: cachectic, normal weight, and overweight. Adipose tissue samples were collected from two anatomical regions: the subcutaneous depot of the flank and the perirenal area. A total of 678 mitochondria from these samples were analyzed using electron microscopy to determine their lengths, thicknesses, and volumes. The average mitochondrial length in cow adipocytes was 0.64 μm (± 0.414), with an average thickness of 0.25 μm (± 0.089). The maximum observed mitochondrial length and thickness were 3.79 μm and 1.13 μm, respectively, while the minimum values were 0.11 μm for length and 0.10 μm for thickness. Notably, a size constraint was observed, with most mitochondria falling within the length range of 0.7-1.2 μm and thickness range of 0.4-0.6 μm, suggesting potential structural or functional limitations. Mitochondrial volumes were calculated to assess expansion or contraction across different BCS categories. The subcutaneous flank region exhibited similar mitochondrial volumes in both cachectic and overweight groups (0.028 μm³), while the perirenal adipose tissue exhibited the highest mitochondrial volume in the normal weight group, suggesting a non-linear relationship between mitochondrial size and body condition. These findings provide new insights into the role of mitochondrial size dynamics in adipocyte metabolism and their potential impact on metabolic regulation in dairy cows with varying body conditions.