The use of TiO2 as digestibility marker in equine

Abstract

Correct and well-balanced nutrition of the horse will improve wellbeing, health and performance. Formulation of well-balanced diets depends on accurate determination of the energy value of any feedstuff, as well as of the total diet. The energetic value of feeds is closely related to their organic matter digestibility (OMD) and this assumption is the underlying basis of feed evaluation systems. Accurate information on OMD of feeds for animals is obtained by conducting in vivo digestibility experiments. In a digestibility trial, the feed under study is given to the animal in known amounts and faecal output is measured. Then, OMD is estimated by subtracting the total amount of organic matter (OM) contained in the faeces from the total amount of OM contained in the feed intake. Therefore, accurate determination of feed intake and total collection of faeces are necessary to determine reliable in vivo digestibility of nutrients in equines. The gold standard for the determination of OMD of feedstuffs is the total collection of faeces, which is time consuming, laborious, requires quantitative separation of urine and faeces and cannot be used with grazing or working horses. Moreover, animals are hindered to express their species-specific behavior due to the collection procedure. Refinement of digestibility experiments, by means of shortening of length of confinement and alternative procedures for total faeces collection are preferred for obtaining equine-specific OMD values. The marker method is suggested as an alternative procedure for indirect quantitation of nutrient digestibility in horses. This method eliminates quantitative collection of the faeces and would enable periodic collection of a representative sample of faeces or even allow grab sampling. The availability of an appropriate marker would minimize interference with animal behavior patterns and might be a potential strategy in order to make a reliable estimate faecal excretion or nutrient digestibility. In equine digestibility studies, acid-insoluble ash (AIA), acid detergent lignin (ADL) as internal markers and chromic oxide (Cr2O3) as external marker have been widely used in both grazing and stabled horses. However, these markers do not seem to reflect the digestibility of the feed accurately. Moreover, the use of Cr2O3 as a feed additive is prohibited due to its potential carcinogenicity. Titanium dioxide (TiO2) is presented as a promising alternative to estimate faecal output or nutrient digestibility in different animal species. Although, in horses TiO2 has not been evaluated or validated as a marker yet. The studies reported in this thesis indicate that TiO2 can be used as a digestibility marker as it provides an accurate estimate of faecal excretion and subsequently OMD in equines. In addition, titanium dioxide appeared to be more accurate in its prediction than Cr2O3 and is not systematically affected by the type of forages, the forage-to-concentrate ratio or exercise. The application of TiO2 as digestibility marker, as described in this thesis, can lead to a standardized procedure for obtaining accurate equine-specific values on OMD. This facilitates future exchange of digestibility values of feedstuffs between countries and/or feed evaluation systems.