The role of technology in mitigating heat stress

  

Soaring global temperatures are putting unprecedented pressure on dairy cows, threatening both their productivity and well-being. As heat stress becomes an ever-more urgent challenge, harnessing technology is key to unlocking effective solutions. This study examines how cutting-edge tools can drive advances in environmental optimization, nutritional management, genetic improvement, and intelligent monitoring, offering actionable insights to develop robust, sustainable systems for preventing and controlling heat stress in the dairy industry.

Against the backdrop of global warming, heat stress has become a major challenge for the dairy industry. It adversely affects cow health and diverts energy from milk production to thermoregulation, leading to reduced milk yield and significant economic losses.

Heat stress indicators
Heat stress is a systemic physiological disorder that occurs when ambient temperature exceeds an animal’s maximum heat-dissipation capacity, resulting in impaired thermoregulation.

There are 3 main evaluation indicators:

Heat stress in dairy cows can be classified using the temperature–humidity index (THI). Under thermoneutral conditions (THI < 68), cows maintain normal physiological function and metabolic stability. As THI rises to 68–72, mild stress occurs, characterised by reduced feed intake and behavioural changes such as increased standing.
Moderate stress (THI 72–78) results in clear physiological strain, including elevated respiratory rate, increased salivation, higher rectal temperature and a measurable decline in milk yield. At THI ≥ 78, severe stress results in marked thermoregulatory overload, with further increases in body temperature and respiration, as well as disruptions in acid–base balance and milk composition.
When THI exceeds 80, cows experience extreme stress, which may cause lasting damage to mammary tissue and negatively affect reproductive performance, including long-term impacts on offspring development.
Heat stress induces oxidative stress
Heat stress disrupts the cow’s internal balance between reactive oxygen species (ROS) and the antioxidant defence system, making oxidative stress one of the earliest and most damaging physiological responses. Heat stress disrupts mitochondrial electron transport, leading to increased production of reactive oxygen species such as superoxide and hydrogen peroxide. This leads to lipid peroxidation, protein damage (protein glycosylation increases affects milk proteins such as whey protein), DNA damage and cell death (raising mammary epithelial cell apoptosis). Antioxidant defences (such as heat shock proteins and the Nrf2 pathway, which upregulates antioxidant genes) involve attempts to compensate but fail under prolonged stress, leading to an imbalance between oxidative stress and the antioxidant system.

Effects on reproduction
At the reproductive level, heat stress disrupts oocyte development, hormonal balance and uterine microenvironment, leading to decreased conception rates, reduced embryo survival rates, and even transgenerational reproductive damage. Heat stress causes abnormal methylation of the insulin-like growth factor 1 (IGF1) gene, which hinders foetal mammary gland development, leading to an 8–12% relative decrease in milk yield in offspring at the lactation stage (Figure 1).

Figure 1 - Impacts of heat stress on dairy cow reproduction (a-f), including impaired physical condition and reduced feed intake, follicular changes, abnormal oestrous cycles, altered luteal dynamics, and pregnancy-related damages such as embryo losses.

 

Oxidative and endocrine responses to heat stress lead to excessive activation of the hypothalamic–pituitary adrenal (HPA) axis, inducing elevated cortisol levels. This state of high cortisol inhibits the proliferation of mammary epithelial cells, reducing the expression of genes related to milk protein synthesis (decreasing milk yield) and disrupting mitochondrial function in oocytes, thereby reducing sperm motility and impairing gamete quality.

Effects on milk production
At the production performance level, heat stress reduces feed intake, impairs mammary function, causes significant declines in milk yield and quality, and affects the long-term production potential of offspring through epigenetic mechanisms (Table 1). Heat stress disrupts intestinal and nutritional metabolism regulation by impairing rumen function. A reduction in feed or dry matter intake decreases the energy supply required for lactation, further deteriorating milk yield and quality, presenting severe challenges to the economic sustainability of the dairy industry.

 

Strategies to mitigate heat stress
In dairy cow heat stress management, short-term, medium-term, and long-term measures should be comprehensively implemented, supplemented by real-time early warning systems to improve animal welfare and production efficiency while reducing economic losses.

Intelligent monitoring and early warning systems
Infrared thermography (IRT) can detect microvascular dilation signals around cows’ ears, mouths, noses and eye sockets, with a temperature sensitivity of ±0.05 °C, enabling early warning of heat stress 2–3 hours in advance with 92% accuracy. It is relatively easy to operate and can be used directly for herd heat stress monitoring.

The SMARTBOW ear tag system uploads core body temperature and activity data for individual cows every 10 min and, through clustering algorithms, prioritises allocating early-lactation cows (postpartum < 100 d) and high-yielding cows (daily milk yield > 35 kg/d) to cooling areas. It reduces the coefficient of variation of daily milk yield in sensitive groups from ±15 to ±5% (relative coefficient of variation) in summer. It requires sensors, algorithms and data support, but is suitable for large-scale pastures.

Intelligent systems, such as the You Only Look Once Version 5 (YOLOv5) algorithm and Canny edge detection, can be used to identify cow chest and abdominal behaviours. The system assesses heat stress in real time by analysing parameters such as respiratory rate and body temperature fluctuations.

Environmental optimisation and physical cooling
Environmental temperature and humidity can be reduced by providing adequate ventilation and shading, as well as by using cooling equipment such as spray systems and fans. For barn environmental optimisation, the combined cooling system of longitudinal ventilation and high-pressure atomisation, using droplets no larger than 50 μm, provides effective cooling through pulse operation for 30 seconds every 5–10 minutes while avoiding excessive humidity. This mode also reduces water consumption.

By integrating real-time monitoring data and THI data, a real-time early warning system can be developed to automatically activate spray and fan equipment, effectively reducing the adverse impacts of heat stress on dairy cows. Previous research shows that combining intelligent spray equipment with ventilation can increase milk yield by 19.8%.

3D nutritional intervention
Nutritional management plays a key role in mitigating heat-stress responses in dairy cows. Adjusting feed formulas to increase antioxidants, energy, protein, and minerals, while supplementing appropriate vitamins and trace elements, can enhance dairy cows’ heat-stress resistance.

The 3-dimensional nutritional intervention system, comprising: antioxidant defence, energy metabolism optimisation and protein homeostasis regulation, can achieve the dual goals of protecting physiological functions and maintaining production performance. Current management systems integrate these parameters into intelligent feeding terminals, allowing dynamic adjustments to nutritional supply based on real-time temperature and humidity data.

Recent advances in animal monitoring technologies now enable real-time monitoring, identification and isolation of vulnerable animals subject to heat stress. By integrating IoT-enabled single- or multi-sensor farm networks, mitigation measures can also be automated and applied only to the affected animal. In addition, the emerging Artificial Intelligence of Things (AIoT), which combines AI and IoT, is increasingly used because it can detect changes in barn conditions and animal health and respond quickly and automatically without human intervention, improving efficiency and productivity.

Genetic breeding
In dairy, it is important to identify genetic variants that improve heat-stress resistance while preserving desirable production performance. With recent advances in genome editing, genetic improvement no longer depends on the presence of favourable variants within the breed of interest; instead, beneficial mutations can be transferred across populations and species or even designed directly. The development of programmable nucleases such as FokI-based zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and, more recently, CRISPR-Cas9, has made this possible. For example, introducing desirable alleles for heat tolerance or disease resistance into dairy breeds using CRISPR-Cas9 can maintain, and even accelerate, the rate of genetic gain achieved through conventional breeding programmes.

Combining mitigation strategies
In conclusion, the researchers emphasised that combining different mitigation strategies can produce stronger results through functional complementarity, with overall benefits significantly greater than those achieved with a single measure. For example, linking intelligent monitoring systems, such as infrared thermography and SMARTBOW ear tags, with environmental optimisation and nutritional management in real time can create an efficient closed loop of perception, decision-making and action.

This article is based on the publication: 
Heat stress affects dairy cow performance via oxidative stress, hypothalamic–pituitary–adrenal axis, gut microbiota, and multi-dimensional mitigation.
 Frontiers in Veterinary Science, Vol 12, 2025.