February 15-18, 2009 Washington State Convention Center Seattle ...

SLOPE RATIO ANALYSIS IS A ROBUST AND PRECISE WAY TO DETERMINE RELATIVE
BIOAVAILABILITY OF NUTRIENTS FOR AQUACULTURED ANIMALS
Peng Li* and Delbert M. Gatlin III
Department of Animal Science
Texas A&M University
College Station, Texas 77843-2471 USA
lipeng@tamu.edu
Nutrient bioavailability estimation is important, not only for screening ingredients that provide the most cost-effective nutrients,
but also for developing microencapsulation/coating processes to increase retention of certain nutrients and overall utilization
efficiency of aquacultured animals. Traditionally, nutrient bioavailability is obtained either by comparing the minimum requirement
for a specific nutrient in different forms established by broke-line regression or polynomial regression, or by comparing
response indices such as weight gain and feed efficiency of animals fed the nutrient in different forms. Bioavailability of nutrients
can be most precisely estimated by slope-ratio assay. In this assay, graded nutrient intake levels are created by varying the
dietary inclusion level of a particular nutrient or ingredient. The response, such as whole-body nutrient concentration and retention
by animals fed the test ingredient is related to nutrient intake, and the slope of the regression line is compared with that from
animals fed the nutrient from a different source. Our laboratory has used slope ratio analysis to define relative bioavailability
of DL-met vs. methionine hydroxy analog for hybrid striped bass (Figure 1 and 2), seleno-methionine vs. sodium selenite for
hybrid striped bass (Figure 3) and α-tocopheryl acetate vs. α-tocopherol succinate for red drum (Figure 4). We observed the
slope ratio analysis is a very robust and precise method in bioavailability estimation in aquaculture nutrition.
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