WATT PoultryUSA - December 2017 - 41
The slopes of the lines were
103.8 and 103.4 for DL- and
L-Met, respectively. This yields an
RBV estimate of 100% for L-Met.
The 95% CI was from 65% to
134%, indicating no significant
differences in the methionine
sources. Based on feed conversion,
the RBV of L-Met was 89% of
DL-Met with a 95% CI of 31% to
147%, also indicating no significant differences in the sources.
Kong et al (2016) estimated
an RBV for DL-Met using L-Met
as the standard in 13 kg pigs in
a N balance study. The researchers calculated an RBV of 87.9%
for grams of N and 89.3% for
percent N retained. The 95% CI
(56% to 120%, g N; 57% to 122%,
%N) indicate no significant difference between the sources for
either response. These studies all
support a 100% RBV for L-Met
versus DL-Met and are in agreement with other studies that
have found high utilization rates
of the D- form of methionine.
In conclusion, methionine
supplements are best compared
through simultaneous dose
response trials. Data can be fit
to either linear or non-linear
models successfully. The ratio of
the slope of the test ingredient
response to a standard ingredient
provides an estimate of the RBV.
Dosage levels should include the
sensitive range below the nutrient
requirement. Trials using diluted
D,L-Met have validated the use of
slope ratio to accurately predict
the RBV of methionine sources.
The estimate of the slope ratio
must be compared to the 95%
confidence interval or some other
"fiduciary" limits to determine its
significance. Finally, nutritionists and purchasing managers
would benefit from a throrough
understanding of RBV of the ingredients they have available. The
consequences of not knowing the
relative value of different sources
of the same nutrient can have a
huge financial impact on cost of
For references see www.evonik.com/
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