Trouw Nutrition, a Nutreco company, is highlighting the damages producers take from heat stress and sharing data supporting how feed additives may limit financial losses by protecting animal health, oxidative balance and production during periods of heat stress. The presentation - Heat Stress: How to support your animals with feed additives – was part of Trouw Nutrition's global webinar series.

Strengthening heat waves and increasingly warm years are altering how producers experience heat stress. Managing heat stress and the losses it presents is no longer a regional challenge. Heat stress affects animals and producers' economics around the globe. However, economic damages to production wrought by stressful conditions can be minimized or prevented by taking steps to protect animals from the physiological challenges - like oxidative stress, intestinal damage and electrolyte imbalance - generated from high temperatures.

Global temperatures and animal sensitivity

Global temperatures are rising – the 20 hottest years on record were reported in the last 22 years. The European Union indicates there is a 75% chance that 2020 will be the hottest year recorded since the start of record keeping in 1880.

Rising temperatures brings implications for animal producers as several production species including dairy cows, poultry and laying hens, pigs and beef cattle can decline during humid and warm weather. The temperature-humidity index (THI), which was established to make heat stress more quantifiable, indicates what combinations of factors produce heat stress conditions ranging from mild stress through higher mortality.

The THI calculations combine heat with relative humidity to establish the THI index number and determine the level of risk for animals. For example, poultry start suffering from heat stress when conditions combine to reach an 82 or higher on the index, while pigs start to develop heat stress symptoms at 75 and cattle at 72.

Figure 1 – THI chart for cattle

Several factors influence livestock animals' tolerance to heat stress. Some production species, like birds, do not have sweat glands and others have inefficient sweat production. Additionally, animals genetically selected to have high metabolic activity and increased feed intake can generate a larger amount of internal heat. Also, when raised in dense populations there may be less opportunity for animals to dissipate heat from the herd or flock.

Economic damage from heat stress

Annually, it is estimated that heat stress costs agricultural producers about $150bn (€127.7bn) or about $100 (€85.11) per dairy cow.

Stress can reduce feed intake, which limits average daily gain (ADG) and increases the feed conversion ratio (FCR). Temperature conditions also can limit egg production and the quality of eggshells along with reducing milk production. Additionally, lower feed intake and reduced nutrient uptake by the animal can negatively affect the quality of meat or animal-based products produced.

Continuing economic damage may indicate that although producers are taking steps to address heat stress, more needs to be done. Looking at the financial challenge for livestock producers specifically in the U.S., the annual economic damage amounts to about $128m (€108.9m) for poultry, $299m (€254.5) for swine, $365m (€310.6) for beef cattle and $897m (€763.4) for dairy producers. However, those losses only account for directly related adverse effects from heat stress – delayed results may be harder to quantify.

External symptoms of heat stress

Several physical symptoms may suggest animals are suffering from heat stress. In addition to reduced feed intake and slower gain, panting is a common symptom along with reduced production of eggs and milk.

Free radicals and internal damage

In addition to exhibiting external symptoms, animals experience multiple internal changes during heat stress. An initial internal response is the increased generation of free radicals, which damage cells and organelles. There also can be damage to the intestinal barrier – often called a "leaky gut" – which allows greater movement of pathogens and bacteria and can imbalance the microbiota.

High temperatures alter an animal's thermoregulatory response and blood flow is increased to skin and peripheral regions, while the splanchnic blood flow decreases. This shift can lead to internal hypoxia and a reduction in intestinal integrity. Animals also can develop an electrolyte imbalance, alkalosis and dehydration.

Figure 2 – Blood flow changes and cellular damage

Animals also may experience increased immune challenges as the bonds between cells break down providing more space for pathogenic bacteria to move between intestinal walls and to trigger an immune response. Free radicals damage the tight junctions between cells to create spaces for bacteria to move into the blood stream. Free radicals damage proteins and cell membranes by stealing electrons. As more free radicals are created, an increasing amount of damage is done. Free radicals tend to target healthy organs including the heart, liver, lungs and gut.

Additionally, heat stress conditions can exacerbate responses to other kinds of free radical-producing oxidative stress generators like vaccinations, transportation, growth, weather shifts and diet modification.

Figure 3 – Heat stress and free radicals

The panting response to high temperatures can prompt the development of an electrolyte imbalance. As animals pant to cool themselves, the level of carbon dioxide (CO2) in the blood is reduced, which raises blood's pH. The shift in pH can cause an imbalance in electrolytes and increase urination, which increases the risk of dehydration. As dehydration is another side effect of heat stress the condition is exacerbated.

Two-prong approach to prevention and mitigation

Once animals develop damage from heat stress it can be hard to help them recover. However, both farm management practices and feed additives can be used to help prevent or mitigate heat stress-related damage before it takes effect.

Some management steps that can be taken to improve animals' response to heat stress include reducing stocking density, supplying adequate drinking water and feeding when external temperatures are at their lowest. Increasing air speed within a barn or facility to provide additional wind chill can have a positive influence. Management practices may be able to reduce the adverse effects of heat stress by about 30 to 40%.

Feeding strategies to address heat stress

Along with shifting management practices, select types of feed additives can be used to support an animal during heat stress conditions. Feed additive use tends to be less expensive than management changes and has been linked to a 40 to 60% reduction in heat stress response. Additives can be used to help maintain the animal's antioxidant balance, osmolyte balance, and electrolyte balance. Additives also can support intestinal integrity and water intake.

Antioxidants are needed by the animal during production and maintaining antioxidant and osmolyte balance during heat stress is critical to protecting the integrity of the gut. However, during a period of heat stress, it can be important to provide antioxidants that have specific characteristics – including being highly digestible and bioavailable. An antioxidant used during heat stress should be able to navigate internal lipid- and water-based structures because it has a better chance of staying intact and being available to attack the free radicals spreading throughout an animal's body.

Figure 4 – Antioxidants attack free radicals if they can reach them

Not all antioxidants work in the same way and some commonly used antioxidants - like vitamin E - may not provide the best support for animals facing heat stress. Additives like vitamin E, which is attracted to lipid structures, don't have the ability to attack free radicals in multiple locations as they are predominantly focused on one type of structure.

In developing an antioxidant additive for use during heat stress conditions, Trouw Nutrition focused on finding compounds that are both fat and water soluble.

In a feeding study with broilers facing heat stress, birds receiving 10 or 50 parts per million (ppm) vitamin E generated higher levels of the antioxidant superoxide dismutase (SOD) than those receiving 50ppm of the antioxidant feed additive AOmix. The expression and production of SOD is in direct relation to the degree of stress, indicating birds fed vitamin E were facing increased amounts of oxidative stress compared to those pre-treated with AOmix prior to experiencing heat stress.

Figure 5 – Using antioxidants to support heat-stressed poultry

Another way to improve animal response to heat stress conditions is to support gut integrity by maintaining cell osmolarity and preventing the breakdown of intestinal integrity. The feed additive Betain was developed to preserve intestinal wellbeing. The additive helps maintain water retention, cell volume, cell integrity and anabolic activity within the cell.

In a feeding trial exploring the use of the feed additive Betain, animals receiving the additive prior to experiencing heat stress demonstrated improved osmolyte balance and healthier villi in the intestine. Intestinal integrity was stronger for animals receiving the supplement.

Figure 6 – Betain feeding trial results and villi health

Similarly, a feeding trial looking at another antioxidant and osmo-regulating feed additive – Nutricool – found that it could boost feed intake and reduce panting in high heat conditions. Piglets receiving the additive during a heat stress period displayed less panting behavior compared to piglets not eating the additive. Supplemented piglets had a daily feed intake of more than 0.8 kg while those in the control group had a daily feed intake of about 0.6 kg.

Additionally, feed additives can be used to maintain electrolyte balance and water intake. The acute changes from heat stress can alter electrolyte balance, so it remains important to keep that balance along with blood pH, controlling stress hormones and managing water intake.

"Trouw Nutrition, based on mechanisms that are described, has developed products aimed at reducing the adverse effects of heat stress by focusing on antioxidant balance, preserving intestinal integrity, osmolyte balance, electrolyte balance and also water intake," said Soheil Varasteh, DVM and global product manager for Trouw Nutrition's nutritional solutions.

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Article made possible through the contribution of Trouw Nutrition

Managing heat stress via farm management and dietary approaches