A systems approach to the study of grazing management on Canterbury seasonal supply dairy farms

Seasonal supply dairying in Canterbury operates under different conditions to those prevailing in the North Island of New Zealand. This study examines the current grazing management of Canterbury farmers, suggesting improvements which will raise farm profitability. Profitable dairy production is based upon the economic conversion of pasture to milkfat. Control of this production system is improved by understanding the interdependency of the bioeconomic variables which act within and upon the system. Through influencing both animal and pasture production, the level of harvesting forms the key variable. To achieve the desired level of harvested pasture the farmer varies farm grazing pressure by means of available grazing practices which the demand for or supply of pasture. Data relating to the grazing practices of Canterbury farmers were gathered by a postal and interview survey programme. Subsequent analysis revealed that leading farmers outperformed the average by 41.2% in the 1984/85 season. This advantage resulted chiefly from a policy of high stocking rates supported by irrigation, off-farm grazing and purchased supplements. Further assessment of Canterbury grazing management was based upon a mathematical model. The model indicated that a self-contained dairy property (excluding the off-farm grazing of young stock) could produce approximately 628 kilograms of milkfat per hectare. This level of performance is achievable by high breeding index animals because of a better match between their requirements and pasture growth patterns. However this compatibility is lost where excessive amounts of body tissue are mobilised. Off-farm grazing and purchased supplements can be used to further increase milkfat production. The economics of extending the pasture resource in this way are limited. In summary, improving the profitability of seasonal dairy farms is dependent on many factors. Farmers in Canterbury are recommended to concentrate especially on herd improvement, stocking rate and irrigation