Supplying the energy and fiber needs of dairy cows from alternate feed sources.

Alternate feeds are a major resource of the dairy industry. The major issue involving them is a method to predict accurately nutritive value from laboratory analyses. Variation in nutrient content of most alternate feeds is greater than in feed grains. Another issue is which depression factors to use in adjusting values for TDN from maintenance to production intakes. The NRC uses an average depression of 8% for all feeds; others think each feedstuff should be depressed individually, and discount factors have been proposed. For some alternate feeds, large differences in net energy estimates occur. Neutral detergent fiber has been proposed as an indicator of productive energy, but it has several deficiencies with alternate feeds high in fat, molasses, or ash. A summative equation based on fat, ash, protein, NDF, and lignin has wider application for predicting NE1 for all feeds. A roughage value index reflects a feed's property to stimulate chewing and rumination. Its use has special relevance for alternate feeds with small particle sizes, which may induce little chewing. Supplemental fat may increase the metabolizable energy converted to milk, but respiration experiments are needed.