Calculating dry matter consumption of dairy herds in Australia: the need to fully account for energy requirements and issues with estimating energy supply

Feed costs are the major component of the variable costs and a significant component of the total costs of milk production on Australian dairy farms. To improve farm productivity, farmers need to understand how much feed is being consumed and the nutritive characteristics of the diet. This paper reviews an existing simple approach, the 'Target 10' approach, which is commonly used by the dairy industry in Victoria to estimate annual forage consumption. An alternative approach - the 'Feeding Systems' approach - is then introduced. The 'Feeding Systems' approach is compared with estimated forage consumption measured under experimental conditions. An analysis of the sensitivity of both approaches to incremental changes in key variables is presented. The 'Feeding Standards' approach was concordant with estimated forage consumption measured under experimental conditions. Sensitivity analysis has highlighted key variables which may have considerable influence over simulated forage consumption using this approach. Given that none of the key variables tested in this analysis can be varied in the 'Target 10' approach, we feel confident that the 'Feeding Standards' approach provides an improved method of back-calculating annual on-farm forage consumption. Using a robust approach to calculate forage consumption which fully accounts for metabolisable energy requirements is important where farmers are using home-grown forage consumption as an indicator of farm feeding system performance. It is also important to understand the assumptions involved in estimating metabolisable energy supply from either supplements or forage.