A dairy herd model for use in whole farm simulations

A dairy herd submodel was created for integration with other farm submodels to form DAFOSYM, a dairy farm simulation model. The herd submodel determin es the best mix of available feeds to meet the fiber, energy, and protein r equirements for each of six animal groups. The groups are early-, mid-, lat e-, and nonlactating cows, heifers over 1 yr old, and younger heifers. Feed intake, milk production, and manure dry matter and nutrient (N, P, and K) excretions are functions of the nutrient content of the diets. Required fee d characteristics include crude protein, rumen degradable protein, acid det ergent insoluble protein, net energy of lactation, neutral detergent fiber, total digestible nutrients, P, and K concentrations. Feed intake is predic ted with fill and roughage units. These units are functions of feed neutral detergent fiber adjusted for particle size distribution and the relative r ate of ruminal digestibility or physical effectiveness of the fiber. The he rd submodel predicted feed intakes, nutrient requirements, diets, and manur e excretions similar to those recommended or measured for dairy animals. Wh en integrated with other farm components in DAFOSYM, the comprehensive mode l provides a useful tool for evaluating the long-term performance and econo mics of alternative dairy farm systems.