The use of phytogenic silica as internal marker for the measurement of feed digestibility in rabbits

Abstract

Phytogenic silica (PS) is the silicon assimilated from soil and ultimately precipitated into or onto the cell wall structure of plant tissues in an amorphous (SiO2), non-digestible by animals, form. The PS is the major fraction of the hydrochloric acid-insoluble ash (AIA), which is used as an internal marker in feed digestibility studies; however, PS can be quantified by methods more rapid and sensitive than AIA. Therefore, the present study aimed to evaluate PS as an alternative to AIA internal marker for the measurement of total tract apparent digestibility in rabbits. Thirty rabbits were used to calculate the coefficient of total tract apparent digestibility (CTTAD) of dry matter (DM) and gross energy (GE) of the same basal diet according to the European reference method (ERM), the AIA and the PS technique (n = 10 rabbits/method). Total faecal collection was carried out in AIA and PS rabbits to determine faecal marker recovery. The concentrations of AIA in diets and faeces were 12.89 ± 0.066 and 31.58 ± 0.042, whereas those of PS were 13.98 ± 0.066 and 36.59 ± 0.059, respectively (mean±SEM). Faecal marker recovery was 100.3 ± 1.43 % and 100.8 ± 1.48 % for AIA and PS (P= 0.939), respectively. The CTTAD of DM did not differ between methods (P= 0.935) and was 0.589 ± 0.0055, 0.591 ± 0.0056 and;0.588 ± 0.0060 for ERM, AIA and PS, respectively. Also, the CTTAD of GE was similar between all methods (P= 0.914) and was 0.581 ± 0.0058, 0.585 ± 0.0060 and 0.584 ± 0.0064 for ERM, AIA and PS, respectively. The PS determination required less sample quantity (by 98 %) and reagent volumes (by 68–82 %) and had a 7-fold higher sample throughput compared to AIA. In conclusion, PS is a reliable internal marker in rabbits and offers the possibility of calculating the CTTAD of diets with the same precision as ERM.