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 ( δ 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 δ 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 δ 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 13 C 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 δ 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 © 2004 John Wiley & Sons, Ltd.