Abstract

The complex interactions between the biological, physical and management aspects of a farm can be represented mathematically using a computer model. A whole-farm model has been developed that links published sub-models for cow metabolism together with climate-driven pasture models, in a framework that allows for different management options. The model framework is written in VisualWorks Smalltalk, with submodels written in several programming languages linked to the framework using Microsoft COM protocol. Predictions of the whole-farm model have been compared with pasture and animal production data obtained from a dairy system trial at Dexcel in the Waikato. The system consisted of a herd of 19 cows, at a stocking rate of 3.2 cows/ha. The Whole Farm Model was used with Baldwin`s MOLLY cow model of metabolism, the McCall (1984) model of pasture growth, daily climate data and a management policy whereby daily activities on the farm were enacted by the framework. These activities included, for example, assignment of paddock for grazing, closure and cutting of paddocks for conservation, calving and drying off dates of each cow, and supplement feeding. At the end of each season the whole-farm model predicted 75% of pasture growth compared with observed values assessed by visual assessment, 98% of milk yield and 98% of cow live weight. In addition to annual production by the whole farmlet, the whole-farm model can simulate individual animal and paddock production on a monthly and daily basis, so that patterns of change can be compared over the whole season. The whole-farm model is being used as a tool to design and analyse new dairy farm systems.

ME, Wastney, CC Palliser, JA Lile, KA MacDonald, JW Penno, and KP Bright

Proceedings of the New Zealand Society of Animal Production, Volume 62, Palmerston North, 120-123, 2002