The emergence, development and effectiveness of decision rules for pasture based dairy systems

The development of management decision rules resulting from farm systems and component experiments in pastoral dairying over the past 60 years continues to underpin the fundamentals of profitable milk production in both Australia and New Zealand. This is despite a large diversity in dairy farm systems and an increase in the adoption of feeds other than pasture. An understanding of these rules is increasingly important as herd size increases and farm management decisions are often now made by employed farm managers, with limited experience of a property and a district, assisted by consultants using computer simulation models. It is our view that the several varieties of farm management decision rules used, such as the so called "Ruakura No. 2 rules" and the "3-leaf grazing" principle, describe the same proven principles of grazing and animal management for sustained, profitable milksolids production from pasture. They are not fundamentally different and confusion can arise amongst users when they are differentiated. Decision rules may require some adaptation to the environments to which they are being applied. This paper describes the relationships between various decision rules and the principles that underpin them, and the testing that has been done to validate decisions made with computer simulation models against observations made on actual farms.