The chromogen method for determining the digestibility of dried grass by sheep

The total collection method for determining digestibility has been compared with a ratio method that uses as a marker the absorption at wavelength 406 mμ of plant chromogens extracted from the food and faeces. Results showed that when dried grass was fed to sheep the chromogen method gave low results when extracts were read at 406 mμ, and substantially correct results when read at 416 mμ. However, owing to the instability of the plant pigments involved, the plant chromogen method should be applied extensively only after comparative trials have shown that results for digestibilities agree with those found by reliable collection methods. Estimates of the major fat‐soluble plant pigments entering and leaving the alimentary tract showed that there were losses in all pigments during passage down the tract, but whereas losses of up to only 18% occurred in the carotenoids, losses of up to 62% were noted in the total fat‐soluble tetrapyrroles and up to 87% in chlorophylls. The losses varied greatly from sheep to sheep.