Episode 62 – Tackling heat stress and nitrogen management for sustainable dairy farming
In this episode, DairyNZ scientist Dr Kirsty Verhoek explains how heat stress affects cow comfort and productivity, and how the Grazing Heat Load Index (GHLI) improves on traditional measures like the Temperature Humidity Index. Dr Paul Edwards discusses how GHLI, combined with digital technologies, helps farmers identify regional heat stress risks and take timely action. Dr Roshean Woods introduces a new bulk milk urea (BMU) tool that provides near real-time insights into dietary nitrogen surplus, helping farmers optimise herd health and reduce nitrogen loss. Together, they highlight how these tools support farm resilience and sustainability in a changing climate.
Guests:
- Kirsty Verhoek, Senior Scientist, DairyNZ
- Paul Edwards, Science Lead, DairyNZ
- Roshean Woods, Senior Scientist, DairyNZ
Hosts:
- Sheryl Haitana, Editor, Dairy Exporter
- Anne Lee, Deputy Editor, Dairy Exporter
With a background in ruminant nutrition and greenhouse gas emissions, Dr Kirsty Verhoek is a senior scientist at DairyNZ, where she leads research into cow comfort and the impacts of heat stress in New Zealand’s pasture-based systems. Kirsty explains how heat stress occurs when cows can’t offload excess heat, resulting in behaviour changes, reduced feed intake, and lower milk production.
She outlines how international indices like the Temperature Humidity Index (THI) fall short in NZ conditions, prompting the development of the Grazing Heat Load Index (GHLI), which incorporates solar radiation and wind speed. Kirsty also shares how digital technologies, such as rumen boluses and collar sensors, are enabling better detection of heat stress indicators like respiration rate.
Kirsty emphasises the complexity of managing heat stress across diverse regional climates and the importance of tailored, farmer-led approaches. Through DairyNZ’s Enhanced Animal Care programme, she is working closely with farmers to co-develop practical strategies that prioritise cow wellbeing and support long-term farm resilience.
With over 15 years at DairyNZ, Dr Paul Edwards specialises in farm systems research, focusing on heat stress risk for dairy cows. He discusses how his recent work, alongside Dr Kirsty Verhoek, uses digital technologies and climate data to predict heat stress through the Grazing Heat Load Index (GHLI), which forecasts cow respiration rates based on weather conditions. This allows farmers to implement timely mitigations.
Paul highlights the regional differences in heat stress risk, with areas like Waikato, Bay of Plenty, and Canterbury most affected, and the importance of tailored solutions. He also explains his research on how cows use shade, using data from wearable sensors and LiDAR technology to better understand cow behaviour and inform farm infrastructure design.
Paul emphasises that heat stress is an immediate concern, and his research provides farmers with practical, science-based strategies to improve cow wellbeing and resilience to climate change.
With years of experience in ruminant nutrition and environmental science, Dr Roshean Woods is a senior scientist at DairyNZ, where she leads research into nitrogen management and sustainability in New Zealand’s pasture-based dairy systems. Roshean explains the significance of bulk milk urea (BMU) as an indicator of dietary nitrogen surplus, highlighting how it can help farmers monitor herd health and optimise nutrient efficiency.
She outlines the recent development of a BMU indicator tool, designed to provide near real-time data to support farm management decisions. This tool helps farmers identify when there is a greater risk of nitrogen excretion and offers practical guidelines for mitigating environmental impacts, such as reducing nitrogen loss to waterways.
Roshean emphasises the complexity of nitrogen management in New Zealand’s diverse farming systems, and how the BMU tool fits alongside other strategies to improve farm efficiency, boost productivity, and protect the environment.
