Document Detail

The impact of protein quality on stable nitrogen isotope ratio discrimination and assimilated diet estimation.
MedLine Citation:
PMID:  19898979     Owner:  NLM     Status:  MEDLINE    
Accurately predicting isotopic discrimination is central to estimating assimilated diets of wild animals when using stable isotopes. Current mixing models assume that the stable N isotope ratio (delta(15)N) discrimination (Delta(15)N) for each food in a mixed diet is constant and independent of other foods being consumed. Thus, the discrimination value for the mixed diet is the combined, weighted average for each food when consumed as the sole diet. However, if protein quality is a major determinant of Delta(15)N, discrimination values for mixed diets may be higher or lower than the weighted average and will reflect the protein quality of the entire diet and not that of the individual foods. This potential difference occurs because the protein quality of a mixed diet depends on whether, and to what extent, the profiles and amounts of essential amino acids in the individual foods are complementary or non-complementary to each other in meeting the animal's requirement. We tested these ideas by determining the Delta(15)N of several common foods (corn, wheat, alfalfa, soybean, and fish meal) with known amino acid profiles when fed singly and in combination to laboratory rats. Discrimination values for the mixed diets often differed from the weighted averages for the individual foods and depended on the degree of complementation. Delta(15)N for mixed diets ranged from 1.1 per thousand lower than the weighted average for foods with complementary amino acid profiles to 0.4 per thousand higher for foods with non-complementary amino acid profiles. These differences led to underestimates as high as 44% and overestimates as high as 36% of the relative proportions of fish meal and soybean meal N, respectively, in the assimilated mixed diets. We conclude that using isotopes to estimate assimilated diets is more complex than often appreciated and will require developing more biologically based, time-sensitive models.
Charles T Robbins; Laura A Felicetti; Scott T Florin
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2009-11-08
Journal Detail:
Title:  Oecologia     Volume:  162     ISSN:  1432-1939     ISO Abbreviation:  Oecologia     Publication Date:  2010 Mar 
Date Detail:
Created Date:  2010-02-15     Completed Date:  2010-06-01     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0150372     Medline TA:  Oecologia     Country:  Germany    
Other Details:
Languages:  eng     Pagination:  571-9     Citation Subset:  IM    
Department of Natural Resource Sciences and School of Biological Sciences, Washington State University, Pullman, WA 99164-4236, USA.
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MeSH Terms
Nitrogen Isotopes / analysis*
Rats, Sprague-Dawley
Reg. No./Substance:
0/Nitrogen Isotopes

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