Study of the variability of intake estimation in grazing conditions using Titanium Dioxide as external marker

Abstract

Many techniques have been developed for the estimation of dry matter intake (DMI) by animals under grazing conditions. How­ever, the selective intake of pasture grass by cattle incorporates an important source of variability that affects the confidence of the obtained results. The technique based on the external marker titanium dioxide (TiO2) has reported to be a reliable alterna­tive in estimating animal intake. The objective of this study is to compare the TiO2 technique under grazing conditions with respect to three animal intake prediction equations, which were developed under similar conditions of our experiment. The data analyzed correspond to a crossover experiment using 20 Here­ford heifers, grouped into two lots of 10 according to their live weight (LW), and carried out during two periods: winter and spring 2013. In both periods, each lot was assigned to two pas­tures with contrasting initial quality: 65.5% vs. 71.2% dry mat­ter digestibility (DMD); 54.9% vs. 40.9% neutral detergent fiber (NDF), and 11.6% vs. 22.8% crude protein (CP). Each experi­mental period consisted of 8 days of adaptation to the diet plus 5 days of measurements. From the beginning, 10 g of TiO2 per animal were daily supplied. During each measurement period, a fecal composite sample per animal was elaborated from its daily collection per rectum, and its chemical composition was determined. The results of DMI (kg d-1) measured for both pas­tures using the TiO2 technique showed greater variability than the results predicted by any of the three equations.