Adipose Tissue Growth and Cellularity: Changes in Bovine Adipocyte Size and Number

TLDR

Forty crossbred steers aged 11–19 mo were slaughtered every two months and adipose samples from six depots were fixed with osmium tetroxide to quantify cell size and number. Adipocyte diameters were largely monophasic, with kidney fat having the largest cells at 17 mo, growth to 19 mo being driven mainly by hypertrophy, hyperplasia occurring in intramuscular fat 11–15 mo and brisket fat after 15 mo, and intramuscular and brisket depots classified as late‑developing, with cell number per gram better predicting marbling than diameter.

Abstract

Forty crossbred steers of similar birth date and fed the same growing-finishing diet were used to study adipocyte changes in six fat depots during growth from 11 to 19 mo of age. Steers were slaughtered at 2-mo intervals. Adipose tissue samples were obtained from kidney, mesenteric and brisket fat and subcutaneous, intermuscular and intramuscular fat from the 10th to 12th rib section. The osmium tetroxide fixation technique was used for determination of cell size and number. Except for three brisket fat samples, distributions of adipocyte diameters from six different fat depots were monophasic during the age range considered in this study. At 17 mo of age, the mean adipocyte diameter, in decreasing order, was: kidney fat > mesenteric > subcutaneous > intermuscular > intramuscular > brisket fat. Fat deposition during growth to 19 mo of age occurred mainly by hypertrophy of adipocytes. An apparent cell hyperplasia occurred in the intramuscular fat depot from 11 to 15 mo and in the brisket fat depot after 15 mo of age. Based on cellularity characteristics, evidence exists to classify intramuscular and brisket fat depots as late-developing ones. Cell number/ gram of intramuscular adipose tissue was a better predictor of marbling score than was fat cell diameter.