Energy metabolism of broiler breeder hens. 2. Contribution of tissues to total heat production in fed and fasted hens.

In vitro rates of O2 consumption were investigated using excised biopsies from the liver, ileum, magnum, and latissimus dorsi muscle of Hubbard (H) broiler-breeder hens fed four levels of ME intake. Diet had no effect on O2 consumption of any tissue. The overall mean initial O2 consumption (microL of O2 per mg of dry weight per h) for latissimus dorsi, liver, ileum, and magnum tissues were 4.38, 13.33, 10.54, and 8.01, respectively. The Na+ and K(+)-adenosine triphosphatase-dependent respiration (ouabain-sensitive respiration) was 16% of the initial rate for latissimus dorsi, liver, and magnum tissues and 22% for ileum tissues. Fasting heat production of H and Arbor Acre (AA) meat-type hens measured over 3 days following an initial 24-h fast was 219 and 216 kilojoules (kJ) per kg per day (1 kJ = .239 kcal). There were no strain differences in the partitioning of O2 consumption into tissue components of fasted H and AA hens. Fasting metabolism accounted for 75% of the maintenance energy requirement in the hens. The liver, gut, and reproductive tract, which together make up 5 to 6% of BW, account for 26 and 30% of the total energy expenditure in fed and fasted hens, respectively.