Simulation modelfor milk production. II. Modificationsand experimentation

Ernesto Jahn B.1, Luis Sáez T.1, Mario Silva G.2, Gilberto Gutiérrez R.1 e Iván Franco P.1

Eighty one options for milk production with Holstein cows were simulated. The model considers rotational grazing of a white dover (Trifolium repens) - ryegrass (Lolium perenne) pasture. Forage supplement (FOSUP) and concentrates (CONC) can be fed at three seasons, in the year. The amount and digestibility of the supplements can be varied. Calving is 60% in April and 40% in August. Factors such as potential milk production, quantity, digestibility and duration of delivery of FOSUP and CONC, and stocking rate were varied. Options were ordered in an incomplete factorial arrangement. As cows production potential increased, economic returns increased; also, differences between potential and observed production were enlarged. Prolonging the length of FOSUP delivery (120 to 240 days) caused up to 75% increase in returns/ha. Supplementing during 7 or 8 months did not change milk production and economic returns. Varying FOSUP (8 to 14 kg D.M./cow/day) increased milk production 29%, on the average. When FOSUP digestibility was increased from 55 to 70%, the highest response in milk production was 10.4%. Milk production increased as the amount and digestibility of CONC were augmented. Highest returns/ha and lowest cost/lt of milk were obtained at 0.2 kg CONC/kg milk. The effect of stocking rate was highest at low levels of FOSUP.

1 Estación Experimental Quilamapu (INIA), Casilla 426, Chillán, Chile.
2 Facultad de Ciencias Agrarias y Forestales, Universidad de Chile, Casilla 1004, Santiago, Chile.