Heat Stress in Animals

Rising global temperatures and extreme heat waves are becoming increasingly frequent and intense due to climate change, bringing renewed attention to heat stress in animals.

What is Heat Stress?

• Heat stress happens when an animal is unable to regulate its internal body temperature effectively under high external heat.
• Animals naturally try to cool themselves by sweating, panting, lying in shade, or drinking water.
• But when the heat load from the environment exceeds their cooling capacity, their bodies become overwhelmed.
• This leads to a condition where their cells, organs, and systems start malfunctioning. In the short term, this can cause: Heat exhaustion, Dehydration, Rapid breathing or panting, Loss of appetite, Reduced productivity (like milk yield or weight gain)
• In more serious cases, it can lead to: Organ damage, Fertility problems, Hormonal imbalance or even Death.

How Does Heat Stress Disrupt Animal Hormones?

• Animals survive and function normally because of a finely balanced endocrine (hormonal) system, which regulates metabolism, stress response, reproduction, and more. Heat stress throws this balance off.
• Some major effects observed in animals under heat stress:
• Cortisol & HPA Axis Activation: Cortisol is a key “stress hormone” released by the adrenal glands. In heat stress, the HPA axis (hypothalamus–pituitary–adrenal axis) is constantly activated. This leads to elevated cortisol, which initially helps manage heat but later causes chronic stress, immune suppression, and fatigue.
• Thyroid Hormones (Thyroxine and Triiodothyronine): These control metabolism and body temperature. Under heat stress, levels of these hormones drop, which slows metabolism and reduces energy production. In dairy cows and goats, this results in reduced milk yield, sluggishness, and poor growth.
• Reproductive Hormones (Testosterone, Estradiol, LH, FSH): Heat affects reproductive organs and hormones.
  • In males (like rats, pigs), it damages testes, reduces testosterone, and leads to low sperm quality.
  • In females (like cows, sows), heat disrupts ovulation and may cause ‘summer infertility’.
• Insulin and Glucose Metabolism: Cows under heat stress show increased insulin, which reflects altered glucose metabolism and may indicate early metabolic disorders.
• Other Stress Hormones (Catecholamines): Hormones like epinephrine and norepinephrine stay elevated, which puts constant pressure on the heart and blood vessels, risking long-term damage.

Why this matters in India (Basic Animal Husbandry Statistics 2024)?

• India has a large livestock population (especially dairy cattle, goats, and poultry), many of which live in hot and humid
• India’s milk productionhas increased by 78% to reach 239.30 million tonnes in 2023-24. Alongside milk, there has been an increase in meat and egg production as well. While milk growth has slowed in recent years.
• India continues to be the world’s largest producerof milk.
• Milk Production:
  • Milk productionin India grew by 78%, reaching 30 million tonnes in 2023-24.
  • Despite this increase, growth has slowed compared to previous years (5.77% in 2021-22 and 3.83% in 2022-23).
  • India remains the world’s largest producer of milk, but officials stress the need to boost dairy exports.
  • Milk production from exotic/crossbred cattleincreased by 8%, while indigenous cattle saw a larger growth of 76%.
  • However, milk production from buffaloesdropped by 16% in the same period.
• Meat Production: Meat productiongrew by 95% and is estimated to reach 25 million tonnes in 2023-24. India has been experiencing growth in its meat production, contributing to its position as a significant player in global markets.
• Egg Production: Egg productionincreased by 17%, reaching 77 billion eggs in 2023-24. India remains the world’s second-largest producer of eggs, with an average of 103 eggs per person annually.
• Wool Production: India’s total wool productionstands at 69 million kg.