Modelling the economic and environmental implications of reducing biosecurity risk by changing to a self-contained dairy grazing system in New Zealand

Abstract

This study examines the economic and environmental implications of reducing the spread of contagious pathogens and diseases by implementing a self-contained dairy grazing system. Three typical New Zealand grazing-off systems were examined represented by a Waikato farm where all young stock are grazed off the milking platform, a Canterbury farm where both non-lactating cows and young stock are grazed off the milking platform and a Lower North Island farm where two thirds of the non-lactating cows and all young stock are grazed off the milking platform. For each grazing-off system (base), two options were modelled to reduce biosecurity risk: 1) reducing stocking rate to allow non-lactating cows and young stock to be grazed on the milking platform (self-contained); and 2) leasing support land to graze only owned non-lactating cows and young stock (lease). FARMAX and OVERSEER® models were used to predict the economic and environmental implications of each option. The results were tested at different milk prices representing low ($4.25/kg) milksolids (MS), medium ($6.25/kg MS) and high ($8.25/kg MS) prices. The results showed that a self-contained grazing system reduced profitability by at least 15% across all regions and milk prices when compared with the base farms. The self-contained options leached 3–7% more nitrogen and had 7–10% more greenhouse gas (GHG) emissions per hectare, compared with the base and lease options when grazing-off land was accounted for. However, at a catchment level, the land freed by moving to self-contained might be utilised by other farming enterprises that might have a different environmental footprint compared to dairy grazing.