ABSTRACT

Background and Aim: High ambient temperature (HTa) is a major environmental challenge affecting the welfare, physiological stability, and productivity of dairy ruminants raised in tropical and subtropical regions. Heat stress caused by HTa compromises feed intake, acid–base balance, water metabolism, thermoregulation, and milk production. This review summarizes the physiological, behavioral, and endocrinological responses of dairy goats and cows exposed to HTa conditions and highlights the potential role of high dietary cation–anion difference (hDCAD) supplementation as a nutritional strategy to mitigate heat stress. Under HTa conditions, dairy ruminants increase respiratory rate and panting to enhance evaporative heat dissipation, which may induce respiratory hypocapnia and alter electrolyte balance. The reviewed evidence demonstrates that hDCAD supplementation improves heat dissipation efficiency by increasing nocturnal water intake, expanding body water compartments, and supporting hydration status, thereby reducing rectal temperature increments during daytime heat exposure. In addition, hDCAD positively influences ruminal fermentation, nutrient digestibility, eating behavior, and dry matter intake. Long-term supplementation also promotes renal compensatory responses that help restore acid–base equilibrium. The concept of hDCAD as a “biological coolant” is proposed based on its ability to support physiological cooling mechanisms rather than solely improving feed intake or buffering capacity. This nutritional approach may improve animal comfort and productivity under tropical HTa conditions and could complement existing environmental heat mitigation strategies in dairy production systems. Further investigations in dairy goats and cows under practical farming conditions are required to strengthen the application of hDCAD as a sustainable heat stress management strategy. 

Keywords: acid-base balance, dairy goats, dietary cation-anion difference, evaporative heat dissipation, heat stress, livestock welfare, thermoregulation, tropical climate.