An experiment was conducted to define a protocol to determine metabolizable nutrient and energy values of diets. The metabolizability (M) was calculated of the dry matter (DM); crude protein (CP); gross energy (GE) and AMEn of a single diet. Eighty-one 21-day old (d) male birds were used. The tested methodologies were: Cr2O3 (0.5%) as an indicator (partial collection) or Fe2O3 (1%) as a marker; fasting (0, 4, 6 and 8 h) prior to excreta collection and at the end of the feeding period on the last day of collection (total collection). The excreta collection periods were also tested (3 and 5 days). Twenty 31-day old male broilers from the same group of birds were used to assess the effect of fasting on digestive organ weight. At the end of fasting the digestive organs were removed and weighed. Metabolism coefficients and energy were not different between 3 and 5 days of total collection. CPM was lower for marker utilization and 3 days excreta collection compared to the total collection. Eight hours fasting resulted in significantly lower CPM compared to the other periods or the no fasting. With the methodology of partial collection with 5 days of collection, the lowest values were observed for all the responses, compared to the 3 day collection period. The use of the total collection methodology produced the highest DMM and CPM compared to partial collection. No influence of fasting was observed on the digestive organ sizes, indicating that until 8 hours of fasting no changes were observed in either relative or absolute organ weight. However, the relative jejunum weight of birds submitted to 4 hours fasting was higher than that of birds under no fasting. Total collection, during a 3 day period, without fasting and marker use, is the best methodology for ingredient and feed evaluation of growing birds.
chromic oxide; excreta collection; fasting; ferric oxide; metabolizable energy organ size
