PLANT CHROMOGENS AS AN INDICATOR IN ESTIMATING THE DIGESTIBILITY OF FORAGE CROPS BY SHEEP

Abstract

Digestibilities of 28 forages were determined in conventional digestibility trials with sheep. The concentration of chromogens was measured as the absorptivity at 406 mμ in extracts of the forages and resultant feces. The concentration of extracted chromogens was found to be affected by light, temperature, and time.The regressions of the digestibility of the forages on the concentration of chromogens in both the forages and the resultant feces were significant at P < 0.001. However, the data varied too much for a reliable estimation of the digestibility from the concentration of chromogens in either forages or feces. The recovery of chromogens from the feces was unsatisfactory for determining the digestibility by the chromogen-ratio method in 26 of the forages studied.An examination of the visible spectral absorbance curves of the chromogens suggested a consistent absorption peak for the forage extracts at 413 mμ. In each case the resultant feces curve crossed the forage curve on both its slopes. These intercepts are suggested to account for the two isosbestic points (406 and 415 mμ) proposed by other workers. However, in this study the intercepts varied too much to suggest that either of them would be reliable for measuring the concentration of chromogens for digestibility determinations.