Alteration of the carbon and nitrogen stable isotope composition of beef by substitution of grass silage with maize silage

This study investigated the effect of substituting grass silage (C-3 photosynthetic plant product) with maize silage (C-4 photosynthetic plant product) on the natural abundance carbon (delta C-13) and nitrogen (delta N-15) stable isotope composition of bovine muscle tissue. Forty-five continental crossbred heifers were assigned to one of three diets consisting of 3kg of a barley-based concentrate plus grass silage, maize silage or an equal mixture (dry matter basis) of grass silage and maize silage, fed ad libitum, for 167 days. Substitution resulted in less negative delta C-13 values (P < 0.001) in lipid-free muscle and in lipid, and also a lower delta N-15 (P < 0.001) in lipid-free muscle. Feeding of maize silage was clearly reflected in the delta C-13 of muscle, with each 10% difference in the dietary C-4 carbon intake resulting in a 0.9 to 1.0%. shift of delta C-13 in lipid-free muscle and a 1.0 to 1.2 parts per thousand in lipid. Minimum detectable mean differences (95% confidence, power 0.80, n = 15) in this experiment were about 0.5 parts per thousand and 1.0 parts per thousand for delta C-13 of lipid-free muscle and lipid, respectively, and about 0.5 parts per thousand for delta N-15 of lipid-free muscle. The power analysis presented here is useful for estimating minimum isotopic differences that can be detected between any two groups of beef samples with a given number of replicates. It is concluded that carbon stable isotope ratio analysis of meat can be used to quantify C-3/C-4 dietary constituents in beef production. Copyright (c) 2005 John Wiley & Sons, Ltd.