Postnatal development of stearoyl coenzyme A desaturase gene expression and adiposity in bovine subcutaneous adipose tissue

This investigation addressed the hypothesis that stearoyl coenzyme A desatu rase (SCD) gene expression would serve as a postnatal marker of adipocyte d ifferentiation in bovine s.c. adipose tissue; Samples of tailhead s.c. adip ose tissue were obtained by biopsy from preweaning steer calves 2.5 wk, 5 m o, and 7.5 mo of age and from yearling steers 12 mo of age. Samples also we re obtained at slaughter when the steers were 18 mo of age. The steers samp led as yearlings were fed native pasture from weaning until 12 mo of age, a nd the steers sampled at slaughter were fed a high-concentrate diet from 12 to 18 mo of age. Major peak adipocyte volumes for the 2.5-wk-, 5-mo-, and 7.5-mo-old steers were 14, 270, and 700 pL, respectively (P < .001). The st eers did not gain weight during pasture feeding, and at 12 mo of age peak a dipocyte volume had decreased (P = .009) to 270 pL. At this time, a second, smaller population of adipocytes had appeared with a peak volume of 115 pL . At slaughter, adjusted fat thickness of the steers was 1.60 +/- .13 cm, t he USDA yield grade of the carcasses was 3.51 +/- .31, and peak adipocyte v olume had increased (P = .01) to over 2,500 pL. The number of adipocytes pe r 100 mg of adipose tissue doubled (P = .006) between 2.5 wk and 5 mo of ag e, concurrent with the nearly 20-fold increase in peak adipocyte volume, in dicating that this was a period of apparent adipocyte hyperplasia. Uncoupli ng protein mRNA was undetectable at all stages of postnatal growth, indicat ing that differentiating tailhead s.c. adipocytes do not acquire brown adip ocyte characteristics postnatally. Lipogenesis expressed on a cellular basi s was low in all preweaning samples and increased significantly above prewe aning values only in the 18-mo-old steers. Stearoyl coenzyme A desaturase m RNA concentration also was low in all preweaning samples, but it peaked (P = .07) at 12 mo of age. Because the peak in SCD mRNA concentration preceded a significant rise in Lipogenesis and lipid filling, we conclude that the level SCD gene expression may be indicative of the extent of terminal diffe rentiation in bovine tailhead s.c. adipose tissue.