Characterization of Adiposity-Associated Changes in the Adipose Tissue of Peripartal Dairy Cows

Robert DyerModern nutritional programs in the dairy industry have been designed to increase adiposity during late lactation. Energy stored as fat is subsequently mobilized to support deep nadirs in lactational energy drain in the next lactation. Human and murine obesity models showed nutrient overburdened adipose tissues developed adipocyte hypertrophy and increased inflammatory and immune cell infiltration that led to inflammation (metabolic inflammation). Very little is known about the implications of increasing adipose tissue mass on metabolic inflammatory disorders in dairy cattle even though insulin resistance, dyslipidemia, and steatohepatosis are associated with heavy lactation. Accordingly, the purpose of this study was to begin to relate adipocyte area and immune cell infiltrates in bovine adipose tissue to adiposity. We hypothesized that bovine adipocytes expand in size (hypertrophy) in direct proportion to increased states of adiposity, and that immune and inflammatory cells exist as endogenous inhabitants of these adipose depots. Tissues were collected from mesenteric, omental, and subcutaneous adipose tissue (AT) depots of lactating Holstein dairy cows. Tissues were either fixed, stained and mounted to measure adipocyte size, or digested for isolation of the AT stromal cell fraction (ASCF). Isolated mesenteric ASCF cells, along with mesenteric lymph nodes (positive control), were fixed and stained for flow cytometric analysis. Mean mesenteric and omental adipocyte sizes increased in direct proportion (r=0.85, r=0.87) to body condition score (BCS) indicating hypertrophy, whereas mean subcutaneous adipocyte area was weakly correlated with BCS (r=0.59). Moreover, adipocyte hypertrophy caused a shift in the frequency distribution of adipocyte size toward larger cell sizes. Mesenteric ASCF contained 12.7%??4.3 CD11b+ macrophages/dendritic cells, 14.8%??8.7 CD172+ macrophages, and 7.9%??1.1 CD3+ T lymphocytes on average (n=3). These data indicated that dairy cows respond to nutrient burdens with hypertrophic responses in adipocytes across mesenteric and omental adipose tissue, parallel to adipocyte responses in human and murine models of obesity. Likewise, the results suggested that subcutaneous adipose tissue (SAT) was a highly variable depot which was not as closely regulated as visceral adipose tissue. FACS analysis of mesenteric ASCF showed that endogenous populations of T lymphocytes and macrophages/dendritic cells exist in the mesenteric adipose tissue. Collectively, the data suggests immune functions may impact metabolic homeostasis in bovine visceral adipose depots.Pre-Veterinary Medicine and Animal Bioscience