Heat Stress in Indian Cattle: An Interdisciplinary Review of Physiology, Genetics, Nutrition, Reproduction, Health, Production, and Policy

Abstract

Heat stress has become a persistent constraint on cattle production in India because environmental heat load interacts with high metabolic heat production, breed composition, humidity, solar radiation, housing, water availability and management. This critical narrative review integrates evidence spanning thermal physiology, cellular stress biology, genetics and genomics, nutrition, reproduction, immunity, welfare, milk production, farm economics and public policy. The literature indicates that heat stress is not adequately represented by a single universal temperature-humidity index threshold. Responses vary with breed, milk yield, physiological state, prior acclimatisation and local climatic conditions, and animal-centred measures are therefore needed alongside environmental indices. Indigenous Bos indicus breeds such as Sahiwal and Tharparkar generally show greater thermoregulatory and cellular resilience than high-yielding taurine-derived and crossbred cattle, but this advantage is relative rather than absolute. Recent Indian transcriptomic, epigenetic and phenotypic studies show that thermotolerance involves coordinated regulation of heat-shock responses, metabolism, redox balance, endocrine function and immunity. Nutritional interventions can support water, electrolyte and nutrient balance, yet effects of individual supplements are inconsistent and should not substitute for shade, ventilation, water access and context-appropriate cooling. Reproductive impairment extends from follicular and oocyte function to semen quality, early embryos, gestation and calf development, while immune and welfare consequences can occur even when milk yield appears maintained. Production and economic evidence demonstrates substantial vulnerability but also marked heterogeneity among breeds and systems. India already has strong dairy-development, indigenous-breed and climate-resilience institutions; the principal policy gap is the limited operational integration of heat-resilience phenotypes, climate-linked genetic evaluation, farm-level heat-risk surveillance, resource-efficient abatement and equity-sensitive extension. A durable response therefore requires selection for resilient productivity, locally validated phenotyping, low-resource cooling and nutrition packages, reproductive protection across life stages, and policy coordination across breeding, animal health, climate services and dairy infrastructure.