Stable carbon isotope analysis of different tissues of beef animals in relation to their diet

As part of a larger experiment, 31 young bulls, divided into three groups, were given different diets containing either C-3 plants or a combination of C-3 and C-4 plant-based feeds in three feeding periods before slaughter. Variation in the proportion of C-4 plant material in the diets was made by including or not maize or maize-derived ingredients, whereas the other dietary constituents were from C-3 plants. Analysis of stable carbon isotope ratios (delta(13)C value) was performed on different tissues taken at slaughter: blood, plasma, liver, kidney fat, hair, muscle and ruminal contents. Blood and plasma samples were also taken at the beginning of each period. A highly significant difference was found in the delta(13)C values of blood and plasma samples taken from animals that had received a diet of only C-3 plants or with 59% C-4 material for 70 days. The delta(13)C values of all different samples taken at slaughter were highly significantly different between the three feeding groups that had received diets with 0, 13.5 or 35% C-4 material for on average 137, 139 and 83 days, respectively. For the three groups, samples of hair, muscle, plasma, whole blood and liver were significantly enriched in C-13 compared with the diet (except for liver in one group), whereas kidney fat was significantly depleted. The proportion of C-4 plant material could be accurately estimated from the delta(13)C values of different tissue samples. Stable carbon analysis of different tissues from beef animals can be used to trace back diets containing variable proportions of C-3 and C-4 plant material. Copyright (C) 2004 John Wiley Sons, Ltd.