Discrepancies Between Predicted and Measured Microelements and Toxic Elements in Beetroot Supplemented Diets

Background: Accurate assessment of microelement and toxic element content in animal diets is essential for diet formulation, quality control, and exposure assessment; however, predictive additive models may not fully account for variability arising from raw materials and processing factors. Methods: This study evaluated the composition of microelements and toxic elements in the four diets enriched with 4% beetroot cultivars Boldor and Wodan, either without (level 1) or with (level 3) foliar application of the selenium–based plant growth stimulator. Predicted values (calculated using an additive model P = 0.96 × C basal diet + 0.04 × C beetroot component) were compared with experimentally measured concentrations (M). Four dietary variants Boldor 1, Boldor 3, Wodan 1 and Wodan 3 were analyzed. Elemental concentrations of Fe, Zn, Cu, Cr, Ni, Se, Pb, As, Cd, and Sb were determined using ICP-MS. Results: Substantial discrepancies between predicted (P) and measured (M) values were observed. The largest deviations occurred for Cr, Fe, and Sb. Cr and Sb were generally underestimated by the model, whereas Fe was consistently overestimated. Selenium (Se) showed moderate variability, while Cu, Zn, and Ni exhibited close agreement between predicted and measured values. The largest measured cultivar-related differences were observed for As (2.87-fold), Cd (2.78-fold), Pb (2.47-fold), Cr (2.37-fold), Fe (1.73-fold), Sb (1.57-fold), Cu (1.13-fold), and Zn (1.05-fold), all of which occurred at higher concentrations in Wodan than in Boldor. No statistically significant effect of the selenium–based plant growth stimulator was observed. Conclusions: Overall, the results demonstrate that additive models have limited accuracy in predicting trace element composition in complex diets, particularly for elements potentially affected by raw-material variability, sampling heterogeneity, and analytical uncertainty. The contribution of the dietary 4% beetroot component played a key role in shaping element distribution, particularly for elements with high component-to-basal diet ratios. These findings highlight the importance of proper mixing, prevention of segregation in powdered diets, and strict control of raw material quality.