Computed tomographic precision rate-of-passage assay without a fasting period in broilers: More precise foundation for targeting the releasing time of encapsulated products

The objective of this study was to develop a precision-fed rate-of-passage assay using iodinated contrast as an indigestible marker in broiler chickens. In this experiment, twenty-two Cobb-Cobb male broilers were obtained on the day of hatch and fed a standard corn-soybean meal starter diet until day 21. All birds were then orally gavaged 3 g of feed mixed with 2 ml of iodinated contrast. Two birds were selected for collection of the gastrointestinal tract (gizzard, duodenum, jejunum, ileum, ceca, and colon) at 0:15, 0:30, 0:45, 1:00, 1:30, 2:00, 2:30, 3:00, 4:00, 5:00, 6:00 h post-gavage. A computed tomographic exam of the intestinal tract was conducted to determine the location and percentage of each intestinal segment which contained the admixed contrast and feed. Results indicated that feed entered the gizzard extremely fast after the gavage (less than 0:15 h). The marked feed left the gizzard between the 0:15 and 0:30 h time points and was shown in both the duodenum and jejunum after 0:30 h. We found 67.3% of the duodenum and 48.4% of the jejunum containing the iodinated contrast at 0:30 h time point. After 1:30 to 2:00 h, feed reached the ileum. We found 63.5% of the colon length was occupied with iodinated contrast after 2:30 h, and the contrast was found in ceca 4:00 h after the gavage. The enteric cavity was virtually cleared of the iodinated contrast between the 4:00 to 6:00 h time points, except for a few spots still in the gizzard and ceca. These results indicate that the rate-of-passage can be easily determined in young broilers by using iodinated contrast as a marker without fasting the birds. The digestive time for feed passing through the anterior digestive tract in broiler chickens is less than 2:30 h, with feed arriving at the ceca at 3:00 to 4:00 h. Most of the feed is digested 4:00 to 5:00 h after consumption.