Effects of energy source and feed access on abdominal adipose tissue in chickens of two broiler strains.

Broiler-type pullets of two commercial strains (H & N and Hubbard) were fed either a high fat or high carbohydrate diet from 0 to 20 wk of age. Feeding was ad libitum or restricted to 3 (high-fat) or 3.3 (high-carbohydrate) h/day. Adipocyte characteristics of abdominal fat pads were determined at 5, 8, 11, 17, and 20 wk of age. Birds fed the high carbohydrate diet ad libitum had greater feed and energy intake with no reduction in the efficiency of energy utilization than birds fed the high fat diet ad libitum. The greater energy intake did not increase abdominal fat pad weight. Restricted feeding of the high fat diet produced comparable weight gains, up to 17 wk of age, to those of birds fed ad libitum but at lower energy cost. Adipocyte numbers and mean size were similar for the two strains and responded similarly to the dietary treatments. A characteristic bimodal distribution of cell size, consisting of a primary population of large adipocytes and a secondary population of small adipocytes, was apparent in 5-wk-old birds fed ad libitum. The secondary population of adipocytes in the feed-restricted birds appeared by 8 to 11 wk of age. Lipoprotein lipase activity in the adipose tissue was determined at 20 wk; White Leghorn hens were used for comparison. Consonant with the larger adipocytes, enzyme activity was higher in the broiler-type birds.