Subcutaneous adipose tissue development in Yorkshire (lean) and Ossabaw (obese) pigs.

Subcutaneous adipose tissue development was studied in Yorkshire (lean) and Ossabaw (obese) pigs. Three pigs of each breed were slaughtered at 1 to 2 (group 1), 14 to 20 (group 2), 56 to 70 (group 3) and 180 (group 4) days of age. Formalin and(or) Bouin's fixed paraffin sections were analyzed by various staining procedures. Fresh frozen sections were tested for lipid, esterase activity and glycogen. Fat cell size increased with age in the Ossabaw pigs. Fat cell size was similar for group 1 and 2 Yorkshire pigs. Transitional cells between spindle-shaped. basophilic cells and multilocular adipocytes were present in group 1 Yorkshire pigs. The transition was characterized by a loss of cytoplasmic basophilia and a change in nuclei size and shape. The nuclei of presumptive preadipocytes and small multilocular adipocytes contained one to three prominent nucleoli surrounded by an evenly dispersed, pale staining chromatin material. Cells with identical nuclear morphologies and little apparent cytoplasm were observed in adipose tissue of Ossabaw and Yorkshire pigs of all age groups. The frequency of multilocular adipocytes (percentage of the total adipocytes that were multilocular) decreased during the first 2 weeks of life in both breeds. In age group 3, multilocular adipocytes were more numerous in Ossabaw pigs than in Yorkshire pigs (20 vs less than 1%). Capillary histological and histochemical changes were associated with adipocyte hypertrophy in the younger pigs of both breeds.