Nutrient oxidation and lipogenesis in hens

Data from previous series of trials with hens were re-evaluated in order to quantify the net nutrient oxidation and lipogenesis by combining data from balance experiments and indirect calorimetry measurements. The experiments were carried out with 62 laying hens during the laying period from 26 to 4 7 weeks of age. The hens originated from two strains (A and B), being kept in battery cages either individually or three hens/cage and fed ad libitum with an identical commercial diet. Oxidation of protein, carbohydrate and f at was calculated from gas exchange measurements and nitrogen excretion in urine. The partition of digested protein between oxidation (34%) and retent ion in eggs and body (55%) was nor influenced by the housing system. Howeve r, the generic origin of hens affected protein utilization with relatively lower ox;dation and higher retention in strain B. The main part of carbohyd rate group (CHO-group) was oxidized (45-60%), bur hens kept individually ox idized more carbohydrate than those kept at three hens/cage, as well as the re were significant differences between the strains. The higher use of carb ohydrate fur oxidative processes was coherent with reduced lipogenesis whic h constituted 21% of CHO-group from individually kept hens and 18% from thr ee hens/cage in strain B compared with 31% for three hens/cage in strain A. Generally about half of the FAT(-group) originated fi om lipogenesis from carbohydrate, indicating the importance of lipogenesis to fat retention in eggs. The amount of oxidized fat depended on energy supply from carbohydrat e, hence with higher use of carbohydrate for oxidation in strain B less far was oxidized and more was used for far synthesis.