Digestibility Determination Using Index Compound

The total collection method involves laborious quantitative records of feed intake and output whereas the index method can avoid these laborious procedures, but greatly relies on accurate chemical analysis of index compound in the feed and fecal output. In the use of an index, there are inherent fundamental assumptions which include that index compound should be i) completely inert in the gastrointestinal tract, ii) completely and regularly excreted, and iii) uniformly mixed with the digesta or fecal material. Thus, the amount of index compound in the feed and the amount voided in the output should be uniform over equal periods of time (Adeola, 2001 ). Several index compounds including chromic oxide, titanium dioxide and insoluble ash are commonly used for the determination of digestibility (Jagger et al., 1992 (link); Betancourt et al., 2012 ; Kim et al., 2012 (link); Olukosi et al., 2012 (link)) and are added to the diet at 0.1% to 0.5%. With the index method, digestibility is calculated as follows:
where CI_input and CI_output are the concentration of index compound in feed and feces, respectively; CC_input and CC_output are the concentration of component in feed and feces, respectively.