Climate Change and Its Impact on the Dairy Sector: Adaptation Strategies for a Sustainable Future

Climate Change and Its Impact on the Dairy Sector: Adaptation Strategies for a Sustainable Future

Nidhi Daroch^1*

¹PhD Scholar, Division of Animal Genetics and Breeding, ICAR-National Dairy Research Institute, Karnal, Haryana, 132001

^*Corresponding Author: darochnidhi94@gmail.com

Abstract

Climate change has emerged as a major challenge to global agricultural sustainability, with the dairy sector being particularly vulnerable to rising temperatures and increasing humidity. The continuous increase in greenhouse gas emissions has intensified heat stress conditions, adversely affecting livestock productivity, reproduction, health and overall welfare. Dairy cattle, especially high-yielding breeds such as Holsteins, are highly susceptible to thermal stress in tropical and sub-tropical regions. Among the various indicators used to evaluate thermal stress, the temperature–humidity index (THI) is widely accepted as a reliable measure for assessing the severity of heat stress and its impact on dairy performance. Elevated THI levels are associated with significant reductions in milk yield and quality, impaired reproductive efficiency, and increased physiological strain on animals. This article reviews the relationship between climate change and heat stress in dairy cattle, emphasizing the role of THI as an effective tool for monitoring environmental stress conditions. It further discusses the consequences of elevated THI on dairy production and highlights the importance of adopting suitable adaptation and mitigation strategies to sustain dairy productivity and animal welfare under changing climatic conditions.

Keywords: livestock sustainability, THI, heat stress, adaptation strategies, mitigation strategies, animal production

1. Introduction

The global average temperature has increased by approximately 0.8°C to 1.2°C over the past century, primarily due to anthropogenic greenhouse gases (GHGs) such as carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and halocarbons, according to the Intergovernmental Panel on Climate Change (IPCC). If the current trend continues, global warming is projected to reach 1.5°C between 2030 and 2052. These climatic changes are not only environmental concerns but also have significant and measurable impacts on food security and livelihoods, particularly within the dairy industry.

Elevated ambient temperatures adversely affect livestock production by reducing growth rates, impairing reproductive efficiency, decreasing milk yield and quality, and weakening overall animal health. High-producing dairy breeds such as Holsteins are especially vulnerable in tropical and sub-tropical regions, where high temperature and humidity prevail throughout much of the year. Therefore, developing effective adaptation and mitigation strategies to minimize the impacts of extreme climatic conditions is essential for maintaining dairy productivity in a warming climate.

The temperature–humidity index (THI) is widely recognized as a standard indicator for assessing heat stress in dairy cattle and estimating its impact on productivity. In Holstein cows, a THI value between 66 and 68 is generally considered the threshold at which heat stress begins, resulting in noticeable declines in milk production and quality. THI provides a more dependable assessment of heat stress risk than temperature alone, as it reflects the combined effects of temperature and humidity on animals. It also serves as a practical tool for farmers to identify farm areas or housing systems that fail to provide optimal environmental conditions. When THI exceeds 70, cows experience increasing difficulty coping with heat stress, leading to reduced productivity and overall performance. At THI values above 78, milk production is severely affected, while values exceeding 82 are associated with substantial production losses.

2. Heat Stress: Physiological Responses and Production Losses

2.1 What Is Heat Stress?

Heat stress occurs when any combination of environmental factors causes the effective temperature of the environment to exceed the animal’s thermoneutral zone.

Temperatures above the thermoneutral zone trigger a cascade of physiological, anatomical, and behavioral changes, including:

• Reduction in feed intake
• Decline in milk production and reproductive performance
• Decreased physical activity
• Elevated respiratory rate and body temperature
• Increased peripheral blood flow and sweating
• Altered endocrine function

Rectal temperature above 38.3°C is the most widely used clinical indicator of heat stress. A respiration rate exceeding 120 breaths per minute (bpm), compared to a normal rate of 60 bpm, signals significant thermal distress.

• Impact on Milk Production

The effect of heat stress on milk yield is profound and well-documented. Reduced milk yield under heat stress results from associated disruptions in thermal regulation, energy balance, and endocrine changes. During the dry period, heat stress also impairs mammary gland proliferation and development, further reducing subsequent lactation yields. Decline in milk production can reach 10–15% in farms employing cooling systems, and up to 40–50% in farms with no cooling management.

Critically, heat stress effects are more severe in advanced lactations and in higher-producing multiparous cows, as they generate greater metabolic heat during milk synthesis.

2.3 Impact on Milk Quality

Heat stress affects not only milk quantity but also milk composition and quality:

• Casein percentage drops significantly in summer compared to spring.
• Fat percentage and protein percentage in milk show slight average decreases with increasing THI values, though paradoxically, a slight increase in these percentages can be observed at very high THI values which might be the consequence of lower overall milk volume rather than improved composition.

2.4 Impact on Reproduction

Heat stress dramatically disrupts reproductive performance in dairy cattle:

• Conception rates fall sharply, estrus behavior is suppressed, endocrine function is altered, and early embryo development is delayed or interrupted.
• Continuous exposure of bulls to temperatures above 29.4°C leads to decreased sperm concentration, reduced motility and increased morphological abnormalities.

3. Genotype × Environment Interaction: A Hidden Sustainability Challenge

One of the most critical aspects of heat stress in dairy production is the genotype × environment (G × E) interaction. G × E interaction implies that the relative genetic merit of individual animals changes depending on the thermal environment. In practical terms, the best sires in a comfortable thermal environment may not be the best performers under heat stress conditions.

The genetic antagonism poses a fundamental sustainability dilemma: conventional selection for productivity may be inadvertently eroding climate resilience. Addressing this trade-off is essential for a truly sustainable dairy breeding program.

4. Characteristics of a Heat-Tolerant Animal

Understanding what makes an animal heat-tolerant is essential for targeted breeding. Key traits associated with heat tolerance include:

• Body conformation: Long legs, slender build, and large body appendages (dewlap, ears) increase surface area for heat dissipation.
• Coat characteristics: Short, light-colored hair reflects solar radiation and facilitates evaporative cooling.
• Sweating capacity: Higher density and larger sweat glands, as found in Bos indicus cattle, enhance cutaneous evaporative cooling.
• Metabolic efficiency: Lower resting metabolic rate reduces internal heat production.
• Feed efficiency: Higher feed efficiency under stress conditions reduces metabolic heat load.
• Dehydration tolerance: Greater capacity to tolerate water losses from sweating and panting.
• Endocrine adaptability: Flexible hormonal responses to maintain homeothermy.

Bos indicus breeds are demonstrably more heat-tolerant than Bos taurus. Their upper critical temperature for milk production (~35°C) far exceeds that of Holstein cows (~21°C). This difference underpins the widespread use of Bos taurus × Bos indicus crossbreeding in tropical dairy systems.

5. Adaptation Strategies: Toward a Sustainable Dairy Sector

Sustainable adaptation to climate change in dairy production requires an integrated approach combining physical, nutritional and genetic strategies.

5.1 Physical Modification of the Environment

Environmental cooling remains the most immediate and widely adopted heat stress mitigation strategy:

• Shade structures are a cost-effective solution in moderate climates, reducing solar radiation load on cattle.
• Fan systems and sprinklers are particularly effective during night time hours, dissipating heat through convective and evaporative mechanisms.
• Evaporative cooling works well in low-humidity regions while in more humid climates it is most beneficial during daytime hours when relative humidity is lower.
• Free stall housing with adequate ventilation can significantly attenuate heat stress effects though not eliminate them entirely.

It is important to note that even herds with established cooling systems continue to experience significant heat stress losses, emphasizing that physical cooling alone is insufficient for long-term sustainability.

5.2 Nutritional Management

Targeted nutritional strategies can partially offset heat stress effects:

• Feeding during cooler hours(night time or early morning) allows animals to consume feed when heat dissipation is more efficient.
• Increasing feeding frequency spreads metabolic heat load more evenly across the day.
• High-quality protein supplementation has been shown to improve milk yield by up to 11% in heat-stressed cows.
• Energy-dense diets can help compensate for the reduction in dry matter intake that accompanies heat stress.

5.3 Genetic Selection and Breeding for Climate Resilience

Genetic strategies offer the most durable and cost-effective long-term solution for sustainability. Several approaches are being pursued:

5.3.1 Selection for Heat Tolerance

Selective breeding for enhanced animal resilience can be defined as the ability to maintain production performance regardless of weather variation. It has been proposed as a key strategy.

However, the antagonistic genetic correlation between production level and heat stress resilience means that breeding goals must carefully balance both objectives. Simply selecting for higher milk yield will not deliver climate-resilient animals.

5.3.2 Crossbreeding

Crossbreeding of Bos taurus dairy breeds (e.g., Holstein) with Bos indicus breeds introduces heat tolerance alleles while partially maintaining dairy productivity. This strategy is particularly relevant in tropical regions and represents a pragmatic near-term adaptation pathway for many developing country dairy systems.

5.3.3 Genomic Selection and Functional Genomics

Advances in biotechnology are opening new frontiers for climate-resilient breeding:

• Functional genomic stools including microarray analyses, whole transcriptome analysis, genome-wide association studies (GWAS), and next-generation sequencing have identified genes associated with heat tolerance.
• Genes linked to thermo-tolerance have been categorized into those involved in: (i) energy production, (ii) trehalose synthetase subunits, (iii) classical heat shock protein pathways, (iv) protein degradation, and (v) oxidative stress reduction.
• Heat shock proteins function as molecular chaperones that help animals cope with stress by folding proteins and preventing aggregation of misfolded proteins. They represent promising candidate gene targets for marker-assisted selection.
• The slick hair gene(dominant allele) has been associated with lower body temperature maintenance and improved milk production under tropical conditions offering a specific genomic tool for heat tolerance selection.
• Random regression models incorporating THI as a covariate have proven particularly useful for estimating genetic parameters across the thermal gradient and identifying genetically superior heat-tolerant animals.

5.3.4 Including Multiple Lactations in Breeding Programs

G × E interactions due to heat stress intensify in advanced lactations. Research consistently shows that genetic variance for heat tolerance is substantially higher in second and third lactations than in first. Breeding programs that include only first-lactation records therefore significantly underestimate the genetic basis of heat stress sensitivity. Incorporating records from multiple lactations is recommended for a more accurate and complete genetic evaluation.

6. Future Directions

The path toward a climate-resilient and sustainable dairy sector requires a multi-pronged research and implementation agenda:

1. Marker-assisted and genomic selection programs that explicitly incorporate heat tolerance traits alongside production and health traits.
2. Integrated breeding indices that reflect the true economic cost of heat stress losses across lactations, rather than optimizing solely for peak production.
3. Development of validated biomarkers for heat tolerance including heat shock protein expression profiles and genomic markers for rapid, cost-effective animal screening.
4. Long-term genetic trend monitoring to detect and reverse the ongoing erosion of heat tolerance that has accompanied decades of high-yield selection.
5. Low methane emission traits included in breeding goals, recognizing that livestock is itself a contributor to the GHGs driving climate change, and that sustainable breeding must address both adaptation and mitigation.
6. Farmer education and extension services to facilitate adoption of cooling technologies and updated nutritional strategies, particularly among smallholder dairy producers in tropical regions.
7. Conclusion

Climate change is not a distant threat, it is an ongoing reality reshaping the economics and sustainability of dairy production globally. Heat stress, mediated through rising THI values, causes measurable declines in milk yield, milk quality, and reproductive performance, with effects that worsen across successive lactations and generations of selection for high productivity.

The failure to account for the genetic sensitivity of dairy animals to heat stress risks a progressive deterioration in performance as global temperatures continue to rise. A sustainable dairy sector demands that climate resilience be explicitly integrated into breeding programs, environmental management, and nutritional strategies.

Animal agriculture contributes immensely to global food security. Ensuring that dairy cattle can maintain productivity under the thermal conditions of the present and future climate is not merely a technical challenge but a moral and economic imperative for feeding a growing world population while securing the livelihoods of millions of dairy farmers, particularly in tropical and sub-tropical regions most exposed to climate extremes.

The time to evolve climate-resilient livestock breeds is now. Through the combined power of advanced genomics, strategic crossbreeding, evidence-based farm management, and sustained investment in research, the dairy sector can chart a genuinely sustainable course through the climate challenge ahead.

References

• West, J. W. (2003). Effects of heat-stress on production in dairy cattle. Journal of dairy science, 86(6), 2131-2144.
• Pereira, A. B. D., Brito, A. F., Townson, L. L., & Townson, D. H. (2013). Assessing the research and education needs of the organic dairy industry in the northeastern United States. Journal of Dairy Science, 96(11), 7340-7348.
• Ravagnolo, O., Misztal, I., & Hoogenboom, G. (2000). Genetic component of heat stress in dairy cattle, development of heat index function. Journal of dairy science, 83(9), 2120-2125.