2020 tied with 2016 as the warmest year on Earth. As climate changes continue to present challenges for livestock producers – even in northern climates – research suggests that feed additive interventions can help manage animal health and performance challenges.

Trouw Nutrition, Nutreco's animal nutrition division, is highlighting research regarding the use of feed additives to support gut barrier function and reduce oxidative stress for livestock experiencing heat stress conditions.

Research on heat stress across different production environments indicates that prevention is the key. 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. They also can support intestinal integrity and water intake. Research results were recently shared during a webinar, "Heat stress: How to support your animals with feed additives." The event was part of Trouw Nutrition's global webinar series.

Heat stress expansion and challenges

Heat stress has become an expanding global concern as temperatures rise around the world. Annually, heat stress is estimated to cost global agricultural producers more than $150bn, according to research done in 2003.1 However, those losses only account for directly related adverse effects from heat stress – delayed results may be harder to quantify.

Symptoms of heat stress include panting and depression and the condition can result in reduced feed intake and lower average daily gain, increased feed conversion ratios and lower performance. Although there are outward signs that heat stress is occurring, livestock also can develop internal damage, including:

* Free radical generation – damaging cells and organelles

* Reduced intestinal barrier function – leaky gut – and increased pathogen penetration

* Microbiota imbalance and reduced resistance to immune challenges

* Electrolyte imbalance and increased blood pH

Despite the stress of climate changes, heat stress damage does not have to occur. Management and feed-based interventions can be used to improve livestock resistance to high heat conditions.

Some management practices strategies support: Feed additives strategies can support:

* Increasing air flow * Antioxidant balance

* Reducing stocking density * Intestinal integrity

* Lowering the temperature of drinking water * Osmolyte balance

* Feeding during cooler parts of the day * Electrolyte balance, water intake

Addressing free radicals and oxidative stress

An initial point of damage for livestock experiencing heat stress is oxidative stress and the generation of free radicals.

Figure 1: Heat stress increases generation of free radicals, which can impair the oxidative balance within an animal and damage cellular membranes.

Antioxidants in feed can help livestock mitigate potential damage by scavenging free radicals, but not all antioxidants function in the same way. To provide optimal protection, antioxidants need to be able to distribute throughout the animal including through both lipid and waterbased structures and have a high digestibility and bioavailability. Those requirements mean that not every antioxidant is suitable for addressing heat stress-based challenges.

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 with the degree of stress, indicating birds fed vitamin E were facing increased amounts of oxidative stress compared to those pretreated with AOmix prior to experiencing heat stress.

Figure 2: Oxidative stress comparison trials examined the use of AO-Mix as an alternative to vitamin E for animals facing heat stress conditions.

In a comparison trial with piglets, two antioxidants were provided – vitamin E and Selko AOmix. The alternative antioxidant has more hydroxyl groups than vitamin E and has lipophilic tail, meaning it moves differently within the animal. Results from the piglet trial were analyzed at Ghent University. Animals were exposed to high heat temperatures, 40°C (104°F), for a 24-hour period. Blood samples were taken before and after heat stress exposure and checked for indicators of oxidative stress – Superoxide dismutase (SOD). When increased levels of vitamin E were provided, there started to be a decline in SOD. However, a smaller amount of AOmix was able to generate similar results.

Figure 3: Supplementing laying hen diets with AO-Mix during temperate and heat stress conditions helped support improvements in laying percentage, egg mass and feed conversion.

Preventing gut damage

Another area where livestock can suffer damage during heat stress is the intestinal barrier. Heat stress generates a thermoregulatory response that can alter blood flow patterns leading to intestinal hypoxia and a breakdown of intestinal integrity. The consequences of damaged intestinal barrier function allow for increased pathogenic movement within the animal.2

Figure 4: Heat stress also can lead to intestinal barrier damage, potentially leaving animals at more risk from pathogens.²

However, maintaining cellular osmolarity or gut function helps cellular barriers stay in place. In a trial done at Nutreco Poultry and Rabbit Research Centre in Spain, 600 broilers were given diets with one of three levels of the feed additive – 0, 1g/kg or 2g/kg – and raised in heat stress conditions for 40 days. Broilers on the higher level of the feed additive saw improved feed conversion, especially through day 14, higher live weight at day 40, improved percentage of breast meat and a slightly reduced mortality level. Broilers eating feeds supplemented with the additive at either level also had higher average daily gain than control group birds throughout the trial.

Figure 5: Feed additives can support gut integrity during heat stress and help livestock improve performance.³

Supporting antioxidant and osmolyte function

Although there are feed additives that can support animal production during heat stress conditions by providing antioxidants or boosting osmolyte function, it is possible to combine those responses. A newly developed feed additive, NutriCool was designed by Trouw Nutrition researchers to both maintain cell osmolarity and reduce oxidation reactions for livestock.

In a heat stress trial with piglets the feed additive was given at 1kg/ton and a control group received non-supplemented feed. Piglets were tracked from weaning until reaching 20kg. Piglets on the supplemented feed saw daily feed intake increase by 36% and panting drop by about 36%.

Similarly, in a trial done in 2017, broilers received one of three diets – a control with no supplement; 0.7kg/ton of feed supplementation for the first 10 days followed by 1kg/ton of feed from day 28 through slaughter; and 0.7kg/ton supplementation only for the first 10 days. Slaughter weight was highest for birds receiving the longer period of supplementation although all supplemented birds saw improved weight compared to the control group. Both groups of birds eating the feed additive saw a similar reduction in mortality compared to the control group.

Figure 6: Broiler chickens saw improved results from use of a blended feed additive during heat stress conditions.

A third trial done in 2020 examined use of the additive at 1kg/ton for 36 days with laying hens. Compared to the control-group birds, layers receiving the Nutricool additive had reduced mortality and saw an increase in the number and consistency of egg produced during heat stress conditions.

Conclusion

Heat stress is an increasing challenge faced by livestock producers globally, which brings economic damage along with production issues. Producers may see reduced feed intake, lower weight gain or reduced generation of meat, milk and eggs from animals experiencing heat stress. Livestock can have internal damage from an increased production of free radicals and complications to intestinal integrity.

"Prevention is the key," said Narendra Venkatareddy, global product manager nutrition solutions for Trouw. "As we can predict heat stress and put some strategies in at once we can reduce the losses and improve profitability."

There are management and feed-based strategies that producers can employ to prevent or mitigate some of the damage done. Supplemental feed additives like AOmix, TNI Betain and NutriCool can be used to provide antioxidants or scavenge free radicals or to maintain gut barrier function to alleviate heat stress leading to improved animal health and performance.

"If heat stress has already happened, help also with the electrolyte balance, water intake and implement some more nutritional strategies with the help of the nutritionist," Venkatareddy said during the webinar.

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Article made possible through the contribution of Trouw Nutrition

Protecting gut health and animal performance during heat stress conditions - Research Insights