Criteria for expressing nutritional values of subtropical grasses

Abstract

The results from digestibility experiments made with 17 different subtropical grasses are discussed. The most suitable criteria for expressing nutritional values are crude protein content, crude protein digestibility, nitrogen balance, dry matter intake, and dry matter digestibility. Feeding standards based on starch equivalents and total digestible nutrients which are used in temperate environments are highly inaccurate when applied to these subtropical species. Large seasonal fluctuations occur in the nutritional value of subtropical grasses. At the height of the summer growing season values are very high and adequate for all forms of animal production. In the winter and early spring the grasses are generally of poor quality and are unable to meet the requirements for producing livestock. At this time the crude protein content and crude protein digestibility are low. Animals are also unable to obtain sufficient energy because the dry matter intakes and dry matter digestibilities of the grasses are low. The very low nutritive values obtained during winter and early spring usually occur after grasses have been killed by frost. Frost resistance is therefore an important criterion in selecting subtropical grasses which will maintain high nutritional values throughout the entire yew.