Simulation model tor milk production. I. Structure and calibration

Mario Silva G.1, Alberto Mansilla M.1 y Ernesto Jahn B.2

A model simulating a system of milk production with Holstein cows was designed. Its structure consists of a main program, which defines pasture and stock production and management. This program can work with several pasture types, by changing the respective experimental information. It can simulate different numbers and sizes of fields, as well as different stocking rates. It uses a first subroutine, describing the cows' intake and weight processes. This subroutine, in turn, calls two other subroutines, related to gestation and lactation. Thus, it is possible to simulate a stock with continuous or seasonal calving, in which lactating, pregnant and dry cows existo These three latter states are regulated according to energetic imputs and requirements. This model assumes that protein is not a limiting factor in any of the diets. It functions with different types and amounts of concentrates, according to the cows' milk production. This supplementation operates for variable periods, according to the purpose of the systems under study. The amounts and quality of these feeds are given as imputs. Calibration showed enough consistency with the existing physical experimentation. The main variables considered in th is stage, were mil k production and Iiveweight, which showed a high correlation between simulate and actual values.

1 Facultad de Ciencias Agrarias y Forestales, U. de Chile, Casilla 1004, Santiago, Chile.
2 Estación Experimental Quilamapu (INlA), Casilla 426, ChiIlán, Chile.