Interpretive Summary: The history of adipocyte and adipose tissue research in meat animals.
By: Jackie Walling
A recent article published in the 2018 February issue of the Journal of Animal Science dives into an extensive history of adipocyte and adipose tissue research in meat animals. This article highlights independent researchers and research groups of North Central-58 and North Central-97 working under guidance of the USDA Cooperative Research Service and Land Grant University system. The article starts with the influence of World War II on carcass composition and then branches into the history of general carcass composition, cellularity research, tissue metabolism, and marbling.
During WWII (1939-1945), fattier pigs were encouraged because lard was used for multiple human uses and the assembly of munitions. With the conclusion of the war, the need for lard and grease was disregarded. Adipose tissue accretion (development) was then targeted because excessive fat deposition led to a decline in production efficiency. Slowly, the body composition of meat animals began changing as lean meat became the ideal.
Analyzing carcass composition began back in the 1860s and with help from articles published by the Reciprocal Meats Conference, techniques for analysis began improving in 1951. This resulted in accurate ways for estimating and locating fat. Assessment of fat content was done by the “weight of fat or lean cuts in relation to the carcass weight” and it was found that increasing age or body weight was associated with fat accumulating faster than protein growth.
As the 1960s and 1970s rolled in, understanding cellular mechanisms of hyperplasia (increase in number of cells) and hypertrophy (increase in size of cells) gave rise to reducing adipose tissue accretion while simultaneously increasing muscle growth. Hypertrophy was influenced by lipid accumulation caused by a concentration of nutrients on adipocytes. To stunt hypertrophy, the idea was to dissipate nutrients to other areas which led to the role of endocrine regulation in meat growth. Two hormones, somatotropin (ST) and beta-adrenergic agonists (BAR), increased muscle growth while decreasing adipose tissue. Recombinant porcine ST was found to target Fatty Acid Synthase and decrease lipid accretion rates by 70%.
The 1970s also brought about tissue metabolism focusing on lipogenesis and lipolysis (specifically de novo lipogenesis (DNL)). Enzyme assays explored these processes and determined the precursors to lipogenesis. During this time, the idea of protein to fat ratios emerged. The larger the animal frame, the more protein increased, but the amount of fat seemed to stabilize. These comparison studies eventually led to hormone control particularly using epinephrine on lipolysis.
Since lipogenesis and lipolysis control fat content, the processes effect meat animal marbling. Location of fat determines flavor, but the leaner the meat, the less flavor it holds. Physiological maturity and chemical changes in the body showed that generally all species had their own patterns for locations of fat, but intramuscular adipocytes carried the highest amount of fatty acids.
The history of adipocytes and adipose tissue provides a background of knowledge to keep the field progressing towards continuous improvement of meat quality.
To read the full article, "The history of adipocyte and adipose tissue research in meat animals," visit the Journal of Animal Science.