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Assessing the Potential Public Health Impacts of the Intensification of Dairy Farming in New Zealand

This page shows Leah Grout's PhD project details:

Title: Assessing the Potential Public Health Impacts of the Intensification of Dairy Farming in New Zealand
Student name: Leah Grout
Background: Over the past few decades New Zealand has seen a rapid expansion in dairy production. The number of dairy cattle increased by more than one million from 2007 to 2012 and currently stands at over five million. New Zealand is also the world’s top dairy exporter and accounts for approximately one third of the global dairy trade. Higher dairy stocking rates have resulted in increased pressure on natural resources with the potential to impact public health.

Dairying is associated with both positive and negative human health effects. One major benefit of dairying is the provision of nutrients and dairy products are a major source of high-quality protein and bioavailable micronutrients (i.e. calcium). The dairy sector is also crucial to New Zealand’s economy, supporting more than 49,000 jobs along the production chain. However, dairy production and consumption is also associated with a number of different human health risks, including zoonotic diseases, occupational injuries and diseases, environmental pollution, antimicrobial resistance, foodborne hazards, and diet-related chronic diseases.

A number of studies have examined the environmental impact of livestock and dairy production in New Zealand, but few of have incorporated the assessment of health effects into their analyses and the potential health benefits are often overlooked. This thesis will provide an broad overview of the New Zealand dairy industry, identify both the positive and negative human health impacts associated with the production and consumption of dairy products, examine selected causal pathways of human health impacts, and discuss the public health significance of the intensification of dairy farming in New Zealand.

Aims: The central aim of this project was to assess the public health significance of the intensification of dairy farming in New Zealand. To that end, research objectives were to:

  1. Establish the main causal pathways of human health impacts associated with dairy production and consumption globally and in New Zealand.
  2. Assess available methods and tools for examining the direct and indirect health impacts associated with agricultural production systems
  3. Examine patterns of dairy production and intensification in New Zealand
  4. Quantify, for selected causal pathways, empirical relationships between relevant exposures and health impacts.
  5. Assess the possible implications of future dairy intensification and environmental change for public health in New Zealand.
Design/methods: This project followed a spatial analytical framework. Descriptive temporal analyses were also included in order to further explore patterns of disease and investigate potential drivers. The goals of the spatial epidemiological analyses were the description of spatial patterns of disease, identification of disease clusters, and explanation or prediction of disease risk.

First, spatial patterns of dairy cattle density, which served as a proxy measure for exposure to dairy cattle and the dairy farm environment, were explored using geographic information system (GIS) techniques. Choropleth maps were then created using GIS for selected zoonotic diseases of interest over time in order to visualize spatial patterns of disease. Furthermore, seasonal patterns of disease were explored using descriptive statistical techniques and time animations in GIS. Next, descriptive statistical techniques were used to determine if there was a relationship between dairy cattle density and disease incidence. Additionally, clusters of disease were detected using the Kulldorff space-time scan statistic. Finally, classification and regression tree models were developed for clusters of campylobacteriosis and cryptosporidiosis and for average seasonal notification rates for both diseases. Building on the results, generalized linear models for seasonal campylobacteriosis and cryptosporidiosis notification rates were developed. While none of these approaches allows for definitive causal inference, they provide insight into potential causal processes.
Research impact: Dairy production and consumption are associated with a broad array of health impacts including zoonotic diseases; occupational hazards; direct and indirect environmental health impacts; antimicrobial resistance; foodborne hazards; diet-related health harms and benefits; and indirect economic, social, and cultural effects. The results of this project indicate that dairy production influences enteric zoonotic disease patterns in New Zealand. However, the relationship between dairy cattle density and disease rates is complex and seems to be pathogen specific. Importantly, local and larger scale environmental characteristics and social factors appear to strongly modulate disease risk. The findings of this project could provide useful input into a comprehensive assessment of the health impacts associated with the dairy sector in New Zealand. Additionally, policy makers should seek cross-sectoral solutions that leverage multiple benefits in order to address the potential impacts of dairy intensification.
People: Simon Hales (University of Otago), Michael Baker (University of Otago), and Nigel French (Massey University) served as supervisors.
Funding: This work was supported by an University of Otago Doctoral Scholarship.