The Estimation of the Dry Matter Consumption of Grazing Animals by Ratio Techniques

Abstract

Because of increased emphasis on grassland crops, it is desirable to have an accurate method of computing the intake and digestibility of forage consumed by grazing animals. Although there have been many investigations and much thought given to the problem, no completely satisfactory method of estimating the consumption of pasture-ranging animals has come to the attention of the authors. The use of ratio techniques for determining digestibility has suggested a plan that should provide the desired information. The problem of determining accurately the feed consumed by grazing animals has been reviewed by Aamodt, Lash, and Garrigus (1). In this review Knott, Hodgson, and Ellington (13) were credited with introducing the concept of a standard cow day as a unit for measuring pasture yields. A standard cow day was defined by these authors as 16 lb. of total digestible nutrients (TDN) from pasture per cow per day. In 1946 Kidder (12) estimated the amount of grass consumed by steers by calculating the TDN requirements for maintenance and deducting the nutrient content of the supplementary feeds. Blaxter and Mitchell (2), Gallup and Briggs (8), and Lancaster (14) suggested that the feed consumption of grazing animals could be determined by taking advantage of tile relationship between fecal nitrogen excretion and dr), matter intake. Forbes (5) claimed that the total fecal nitrogen varies too widely to be of practical use in the manner prescribed by Gallup and Briggs. Forbes and Garrigus (7) obtained concordant results in estimating dry matter intake by lignin ratios and a simultaneous total collection procedure. Reid et al. (15) have proposed the use of an 85 per cent acetone aqueous extract of plant pigments for computing both the digestibility and the dry matter intake of forages. Cook and Harris (3) found the plant pi~nent method, although satisfactory for alfalfa, was not suited for the determiuation of the digestibility or consumption of winter range grass. They found that considerable variation existed in the pigment content of different plants, and these differences were clearly reflected in the urine of animals that had been fed plant species of different chromogen content. A review (17) of pasture committees pasture techniques has been published recently by the joint of the American Society of Agronomy, American Dairy Science Association, American Society of Animal Production, and American Society of Range Management.