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1 USDA/Argicultural Research Service, Pasture Systems and Watershed Management Research Laboratory, University Park, PA 16802
2 USDA/Agricultural Research Service, U.S. Dairy Forage Research Center, Madison, WI 53706
3 Agricultural and Biological Engineering Department, The Pennsylvania State University, University Park 16802
4 Animal Science Department, Michigan State University, East Lansing 48824
5 Puyallup Research and Extension Center, Washington State University, Puyallup 98371
A dairy herd submodel was created for integration with other farm submodels to form DAFOSYM, a dairy farm simulation model. The herd submodel determines the best mix of available feeds to meet the fiber, energy, and protein requirements for each of six animal groups. The groups are early-, mid-, late-, 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 feed characteristics include crude protein, rumen degradable protein, acid detergent insoluble protein, net energy of lactation, neutral detergent fiber, total digestible nutrients, P, and K concentrations. Feed intake is predicted with fill and roughage units. These units are functions of feed neutral detergent fiber adjusted for particle size distribution and the relative rate of ruminal digestibility or physical effectiveness of the fiber. The herd submodel predicted feed intakes, nutrient requirements, diets, and manure excretions similar to those recommended or measured for dairy animals. When integrated with other farm components in DAFOSYM, the comprehensive model provides a useful tool for evaluating the long-term performance and economics of alternative dairy farm systems.
Key Words: dairy herd • model • production • system
Submitted on February 4, 1999
Accepted on August 2, 1999
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