A modified bioassay for energy utilization in newly hatched chicks. 1. Determination of optimum durations for feed withdrawal and excreta collection.

Three experiments were conducted with view of a more suitable bioassay system for determination of energy utilization in newly hatched chick based on the TME assay system. The optimum duration for feed deprivation prior to tube feeding was determined with chicks aged 0, 2, 6, and 13 d old. In order to determine an appropriate duration for excreta collection after feeding, chicks deprived of feed for 24 h were force-fed and energy excretion was monitored every 12 h for the next 72 h. Irrespective of the age, energy excretion decreased to a low level at 24 h after feeding and then reached a constant rate: the endogenous energy excretion. In 0- and 2-d-old chicks, N excretion tended to increase from 12 h after commencement of feed withdrawal. On the other hand, energy excretion in the chicks force-fed paste or pellet of basal diet attained constant rates beyond 24 h after force-feeding at all ages, and the rates of excretion were almost comparable to the endogenous energy excretion for the corresponding age. In the chicks force-fed a high-fat diet, however, 36 h was required for the excreted energy to attain a constant rate. The increase in N excretion was also observed following 24 h after feeding in 1- and 3-d-old chicks. Deutectomy at 1 d posthatch modified the patterns of energy and N excretion after the commencement of feed withdrawal but not TME and TMEn values of diets. A modified bioassay system for the determination of energy utilization in newly hatched chicks based on TME assay system is proposed.