Feed quality and animal performance

Abstract

A sound theoretical definition for forage or feed quality is animal performance. This definition may be useful as a relative comparison among forages when given to growing or lactating animals. Voluntary intake and nutrient digestibility have been used to form indices of forage quality, and most feeding standards and models are based on the assumption that animal performance is related closely to intake of available nutrients. Due to variation in measurements of intake, digestibility, and animal performance, however, relationships used to develop prediction equations for animal performance from intake and digestibility are often less accurate than desired. Some of the causes for inaccurate predictions include nutrient imbalances, environmental constraints on the animals used for measurements, and individual animal differences. Variation in voluntary intake is greater than that for digestibility, and appears to be more important in assessment of forage quality. Yet intake is more difficult to determine in animal trials and to predict from forage characteristics. To be useful in livestock feeding, forage quality information must be available before feeding. Due to expense, labor, time, and amount of the feed required, animal trials are not suitable for screening large numbers of feeds or forages such as those from genetic improvement trials. Therefore, prediction of forage quality from feed attributes taken from small samples is necessary. Chemical composition, in vitro bioassays, and near-infrared reflectance spectroscopy have been used successfully to predict intake and digestibility of defined sample sets such as those from genetic improvement trials, but have been more difficult to implement on unknown or open populations such as producer samples. The challenge to progress in this area is obtaining accurate intake, digestibility and performance data on an adequate number of samples under standardized conditions so that a suitable database is available for development of either robust equations, or equations with sufficient specificity to discriminate among different forage and genetic types.