A modified bioassay for energy utilization in newly hatched chicks. 2. Determination of feed input and procedures to...

Two experiments were conducted to develop a modified bioassay system to determine bioavailability of dietary energy in newly hatched chicks based on the TME assay system. Broiler chicks aged 0, 1, 3, 7, and 14 d old were force-fed or consumed feed ad libitum following 24 h of feed withdrawal to determine the optimum level for feed input. In the second experiment, 7-d-old chicks were force-fed various diets and feedstuffs at three levels following 24 h of feed deprivation. Linear regressions (P < .01) between energy input (X) and excreted energy (Y) were demonstrated irrespective of diets and feedstuffs at any age in Experiments 1 and 2. Endogenous energy loss (EEL), estimated by the regression method and approximated over a small range was lower than EEL estimated using feed-deprived chicks. The TME and TMEn values of diets and feedstuffs calculated using EEL estimated by the regression method were not modulated by the feed input level, whereas those estimated by feed-deprived chicks tended to increase with decreases in the level of feed input. Thus, a modified method for determination of energy utilization in newly hatched chicks based on TME assay is proposed, which seems to have proper physiological and chemical bases.