The Hidden Cost of Heat: How Heat Stress Endangers Young Stock from Day One

Heat stress occurs when the animal’s internal heat load exceeds its ability to dissipate that heat into the environment. In dairy breeds like Holsteins, this imbalance is intensified by their limited skin surface area, thick hair, and low sweat gland activity.

In young animals, the impact is even more severe:

• Calves under one month old begin to suffer physiologically at ambient temperatures above 25°C.
• They exhibit elevated respiratory rates, dehydration, reduced milk intake, and lethargy.
• Unlike adults, calves generate less internal heat from rumination but are also less efficient at managing body temperature due to immature thermoregulation systems.

Colostrum is more than the first milk—it’s a neonate's initial immune defense system. Unfortunately, heat stress during late gestation in cows significantly reduces both the volume and quality of colostrum. Studies have shown that:

• Heat-stressed dry cows produce lower concentrations of IgG antibodies in colostrum.
• The volume of colostrum at first milking is diminished, sometimes by up to 30–40%.
• The absorption efficiency of colostral immunoglobulins in calves born from heat-stressed dams is also lower.

• Reduced blood lymphocyte activity in newborns.
• Smaller thymus size, affecting long-term immune function.
• Increased susceptibility to infections during the neonatal phase and beyond.

Heat stress does not wait for birth to make its mark. Calves exposed to in-utero heat stress (IUHS) –especially during the final trimester – show long-term developmental impairments:

• Poor placental efficiency leads to suboptimal nutrient and oxygen delivery.
• Epigenetic changes alter immune response and future milk productivity.
• Grand-daughters of heat-stressed cows have been observed to produce less milk, a compelling example of multi-generational impact.

While it is nearly impossible to fully prevent heat waves, strategic interventions can mitigate damage:

• Shaded, ventilated resting areas for both dry cows and calves.
• Elevated hutches or igloos to improve air flow.
• Use of bedding materials like wood shavings or sand instead of heat-trapping straw.
• Hydration strategies that include midday electrolyte supplementation on hot days.

• Highly digestible forages.
• Controlled energy density diets with appropriate protein levels.
• Supplements that support immune function and gut integrity.

Even with the best efforts, there are limits to what conventional management can achieve. This is where advanced colostrum supplements and plant-based functional additives come into play.

Emerging research highlights the importance of targeted nutritional support for neonatal calves, especially those affected by in-utero heat stress (IUHS). These calves often show impaired immunoglobulin absorption, increased gut permeability, and elevated oxidative stress. Enhancing passive immunity transfer and maintaining gut integrity are critical to improving survival and long-term productivity.

Recent advances in colostrum processing now allow for immunoglobulin-rich supplements free from specific antibodies like IBR, tailored for optimal bioavailability even under compromised absorption conditions. Similarly, certain plant-based feed additives have demonstrated the ability to stabilize intestinal tight junctions, modulate inflammatory pathways, and support hepatic detoxification. Products such as Sangrovit^® and gently produced colostrum powders (Immune Milk) are being explored within these contexts as part of integrated calf health strategies.
   
 

Heat stress in young stock is a critical issue that affects not only immediate calf health but also long-term productivity and immune competence. Elevated environmental temperatures impair the dam’s ability to produce high-quality colostrum and reduce the passive transfer of immunity to the newborn calf. Furthermore, calves exposed to heat in utero or postnatally experience greater physiological strain, compromised immunity, reduced growth, and higher susceptibility to disease. With climate change making heat stress events more frequent and prolonged, understanding these impacts and implementing preventive strategies has become an essential aspect of modern livestock management.
 

Dr. med. vet. Oguz Calisici, Product Manager Immune Milk, Phytobiotics Futterzusatzstoffe GmbH