Soybean meal apparent digestibility for Litopenaeus vannamei, including a critique of methodology

Resumen

Most trials conducted to examine the apparent digestibility coefficients of nutrients in an
ingredient or a diet use arbitrary levels of inclusion of the ingredients and indigestible marker. The suitability
of the levels typically used has not been critically examined, however, and it is not known whether inclusion
levels affect the results obtained. This trial was undertaken to ascertain the apparent digestibility coefficients
for dry matter, crude protein, and gross energy of dehulled, solvent extracted, toasted soybean meal (SBM) by
combining a control diet (containing 23.7% SBM) with SBM at two levels (15 and 30 %; diets contained
23.7, 34.9 and 46,3% SBM) and two levels of chromic oxide (0.5 and 1.0 %) in the Pacific white shrimp
Litopenaeus vannamei. Four replicate groups of shrimp were fed by hand three times daily and the feces were
collected by siphoning from the tank onto a fine mesh screen. The first fecal strands were discarded to reduce
the effects of coprophagy and intake of material other than feed. To minimize leaching of nutrients, fresh
fecal strands were collected as soon as they were observed. The apparent digestibility coefficients (ADC) for
dry matter, crude protein, and gross energy were calculated for the diets and these data were used to derive the
apparent digestibility coefficients for the SBM at the two levels of substitution.
The dietary inclusion levels of the chromic oxide and SBM acted together to significantly (p<0.05) affect the
ADCs obtained for SBM. Over all the treatments, the calculated ADC for SBM dry matter varied from 61.2 to
84.7%; for crude protein from 89.5 to 102.2%; and, for energy from 78.7 to 100.1%. The ADCs were
generally higher among the diets that contained chromic oxide at 1.0 % than at 0.5 %, but the magnitude of
the difference was different for the two levels of SBM substitution.