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Pasture Quality for Sheep as Estimated by Chromogen vs. Nitrogen Indicators¹

Crops Research Division, Agricultural Research Service, U. S. Department of Agriculture, and University of Minnesota, Departments of Agronomy and Animal Science

Abstract

Comparisons of chromogen and nitrogen fecal index indicators of forage digestibility were made with wether sheep grazing alfalfa, bromegrass and reed canarygrass. The prediction equations of Reid et al. (1952) and Lancaster (1954) were used for chromogen and nitrogen computations, respectively.

Both methods indicated a significant decrease in the digestibility of pastured forages with time within experimental periods, and the digestibility estimates were significantly correlated. Similarly, estimates of DOM intake, derived from estimates of indigestibility by chromogen and nitrogen, were reasonable when compared to the TDN requirements of grazing sheep.

However, the chromogen method was biased in that it yielded low estimates of the digestibility of alfalfa in relation to the grasses. This finding indicated that the chromogen method may give inaccurate evaluations of the relative digestibility of forage species or mixtures.

The nitrogen method ranked the digestibility of the three grazed forages in the same order shown in a conventional stall digestion trial.

¹ Paper No. 6086, Scientific Journal Series of the Minnesota Agricultural Experiment Station, St. Paul. 55101.

² The authors express gratitude to Dr. J. T. Reid, Cornell University, for supplying the factor which allowed expression of chromogen extract concentration in terms of "chromogen units"; also, they are indebted to Mr. L. E. Davis, Graduate Research Assistant, who conducted the conventional stall digestion trial.

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