Usefulness of Chromic Oxide Index Method for Determination of Digestibility of Nutrients in Feeds for Thoroughbreds

In order to confirm the usefulness of chromic oxide as an indicator in the determination of digestibility of nutrients in feeds, two experiments were conducted on 4 male thoroughbreds 5 to 9 years old. In Experiment 1, in order to determine the timing of sampling, the time course of fecal chromic oxide after changing feeds and daily variation of the fecal concentration of chromic oxide were observed. Horses were given Feeds 1 and 2 containing 0.2% chromic oxide for 7 days. Feces were collected in feces bags. In Experiment 2, horses were supplied Feeds 1 and 2 for 10 days and feces were collected in the same way as in Experiment 1 for the total feces collection method and about 200 g of feces at 7:00 and 19:00 for the chromic oxide index method for the last 4 days. Fecal contents of chromic oxide reached a plateau at 48 hr after feeding Feeds 1 and 2 containing chromic oxide and remained constant after that. The digestibility of crude protein, ether extract, nitrogen free extract and crude fiber determined by the chromic oxide index method agreed well with that by the total feces collection method in both feeds. Because the timing of excretion of feces was relatively constant in the morning and evening feeding, it was easy to collect feces directly from the anus with a bucket.