Evaluation of titanium dioxide as an inert marker for estimating faecal excretion in grazing sheep

Herbage intake of grazing ruminants is a crucial information for evaluating grazing systems. Since direct measurement of herbage intake is impossible, it is often estimated based on measurement of faecal excretion and digestibility of ingested herbage. The aim of this study was to evaluate the external inert marker titanium dioxide (TiO2) for estimating faecal excretion. Stall feeding and grazing experiments were conducted in Inner Mongolia, People's Republic of China, to determine faecal recovery of TiO2, time to reach equilibrium of intake and excretion of TiO2 after initial administration, the effects of frequency and time of marker administration and of grab sampling on excretion pattern of TiO2, and to evaluate prediction accuracy of faecal excretion. The overall mean of the recoveries in the different experiments (n = 7) amounted to 1.04 (S.D. = 0.05; range = 0.96–1.09). However, in the stall feeding experiments, faecal recovery of TiO2 was higher (P<0.001) in hay diets than in diets with hay and concentrate feed with 1.08 and 0.99, respectively. Furthermore, faecal recovery was higher for sheep at high (5 sheep/ha) than low (2 sheep/ha) stocking rate (1.07 versus 1.00; P=0.014). The equilibrium of intake and excretion of TiO2 was reached 5 days after initial TiO2 administration. Faecal TiO2 concentrations differed between grab samples obtained at three times within a day. The variation in faecal TiO2 concentration was smaller and accuracy of prediction of faecal excretion was higher with twice than once daily TiO2 administration and grab sampling. In conclusion, these experiments show that TiO2 is a reliable marker for estimating faecal excretion in grazing sheep.