Structural and chemical characteristics which limit the nutritive value of forages

The need for methods for evaluating small samples of forage in the laboratory has been well recognized by agronomists and has led to much interest in animal evaluations of forages and in the problems of feeding standards in animal nutrition. It is obvious that chemical composition of forages determines their availability to the animals that consume them, and that composition along with physical characteristics must be in part responsible for palatability and consumption. Chemical composition of forages and indeed of feeds in general, determines the availability of nutrients and hence true digestibility. Forage plants contain tannins, cutin, estrogenic substances, etc., which affect nutritive value. These are not ordinarily thought of in usual schemes for forage evaluation. The problem in the chemical evaluation of forages lies in characterizing the specific factors which limit availability of nutrients and the consumption of the forage by the animal.