Challenges for livestock industry at peak hot seasons
Global warming has created a massive challenge for the livestock industry, especially in tropical and subtropical zones which contribute most to global livestock production (Renaudeau et al, 2019). In farm animal husbandry practices are intrinsically linked with animal health, production and welfare. To deliver quality animal products and safe food efficiently, farmers must practice good animal husbandry and maintain their animals in peak condition. Moreover, there are nutritional solutions that enhance the resistance of animals in the period of high ambient temperature, leading to heat stress.
Heat stress may weaken the immune system of livestock, reduce the success of vaccination and make them more susceptible to infection leading to a decline in growth performance. Furthermore, heat stress may affect meat color and pH and is recognized as one of the primary influencing factors of meat quality.
Generally, growth performance reduction caused by heat stress is directly linked to a reduction in feed intake, but increasing evidence has shown that heat stress may induce reactive oxygen species (ROS) and cause anti-oxidant system disorders, which affect nutrient absorption and metabolism.
1. What is heat stress?
Heat stress is a non-specific physiological response of the body when exposed to high ambient temperatures, which can break the balance of body redox and result in oxidative stress that affects growth performance as well as the health of animals (Ruizhi Hu et al., 2019). Heat stress (HS) occurs when the amount of heat produced by an animal surpasses the animal’s capacity to dissipate the heat to its surrounding environment. This imbalance may be caused by variations in a combination of environmental factors (e.g. sunlight, thermal irradiation, air temperature, humidity, and movement) and characteristics of the animal (e.g. species, gender, and rate of metabolism) (Lara LJ, Rostagno MH., 2013).
Animals experiencing HS tend to reduce their heat production by limiting feed intake, with subsequent negative effects on growth performance. Therefore, HS has been a great concern among scientists and livestock producers for many decades, particularly in arid (dry, hot all year) and in tropical (wet, hot all year) regions of the world (Abdollah Akbarian et al., 2016).
Two major categories of HS, i.e. “acute HS” and “chronic HS” can be distinguished. Acute HS refers to a short and rapid rise in ambient temperature. Chronic HS refers to a high ambient temperature over a long period of time (days to weeks), permitting acclimazation to the environment (Abdollah Akbarian et al., 2016).
2. What is oxidative stress?
Oxidative stress is commonly defined as an imbalance between pro-oxidants and antioxidants at the cellular or individual level (Lykkesfeldt and Svendsen, 2007). Oxidative stress is a disruption of redox signaling and control (Jones, 2006) which leads to damage of macromolecules such as lipids, proteins, DNA, and disruption of normal metabolism and physiology (Trevisan et al., 1991) leading to loss of cell function, cell death or necrosis (Lykkesfeldt and Svendsen, 2007; Nordberg and Arner, 1991).
3. Heat Stress and Oxidative Stress
Under normal conditions, the oxidation system and antioxidant system of animals are in a state of dynamic equilibrium. Once the body produces too much ROS or the body’s antioxidant system is damaged, the equilibrium will be broken and cause oxidative stress (Kannan, K.; Jain, S.K, 2000). This phenomenon reduces the feed intake of animal and affects the metabolism of the body (Estevez, M., 2015). Reactive oxygen species are one of the free radicals that can exist independently and contain one or more unpaired electrons (Kannan, K.; Jain, S.K, 2000). Generally, ROS and reactive nitrogen species (Estevez, M., 2015) are the primary free radicals that participate in various metabolic reactions in the body. However, some ROS are produced in the free radical reaction process and do not strictly belong to free radicals, though they can directly or indirectly trigger the free radical reaction (Kannan, K.; Jain, S.K, 2000). Mitochondrial dysfunction caused by heat stress is the basis of oxidative stress.
Under acute heat stress, ROS level in the body is rapidly increased and the antioxidant enzyme system also responds rapidly, by which the activity of CAT, SOD, and GSH-Px are increased significantly to remove excessive free radicals (Pamok et al., 2009). After four days of acute heat stress, the GSH-Px activity was increased together with serum malondialdehyde (MDA), which can reflect the degree of oxidative damage in livestock (Pamok et al., 2009). It is reported that heat stress increased the expression of the GSH-Px gene. However, chronic heat stress can break the antioxidant enzyme system and cause the ROS accumulation in the body to induce oxidative stress by decreasing the activity of CAT, SOD, and GSH-Px (Del Vesco et al., 2017). Chronic heat stress increased the muscle ROS level and MDA content with reduced SOD and GSH-Px activity in livestock (Lu et al., 2017).
Furthermore, in the early stages of acute heat stress, the levels of mitochondrial substrate oxidation and electron transport chain activity increase, resulting in excessive ROS. In the later stages of acute heat stress, uncoupling proteins (UCPs) are downregulated and excessive ROS causes damage to the protein, lipid, and DNA, which reduces mitochondrial energy production efficiency and increases production of reactive oxygen species causing mitochondrial dysfunction and increasing the oxidative stress of the body. However, chronic heat stress can reduce the metabolic capacity of mitochondria due to it upregulating the UCPs, downregulating antioxidant enzymes, and depleting the body’s antioxidants reserves which causes accumulation of ROS—breaking the oxidative balance and inducing oxidative stress (Akbarian et al., 2016).
4. How does oxidative stress affect animal?
The imbalance of free radicals in animal cells can affect the growth, health and reproduction of livestock. Free radicals can cause damage cells by reacting strongly to protein molecules, DNA structures and essential fatty acids on the lipid membrane, leading to cell damage and death.
Stress affects the mental and physical conditions through neuro-endocrine-immune reactions. It is this impact that will reduce resistance of animals to environmental pathogens.
Modern centralized breeding systems tend to increase oxidative stress due to overcrowding and risks of disease. During oxidative stress, livestock consume a lot of energy to recover rather than concentrate on production and reproduction, thereby increasing the cost of disease prevention and treatment. As a result, livestock will suffer a lot of health and livestock performance losses. Cell and tissue damage also affects the quality of meat, eggs and milk.
Oxidative stress severely affects livestock productivity and implications for reproductive potential, animal health and livestock product quality.
5. Solutions to optimize livestock performance in peak hot seasons
A thorough understanding of the etiology and pathophysiology of oxidative stress in livestock will allow producers and nutritionists to design specific anti-oxidant stress solutions, in accordance with the status of each farm in each species of pet. Here are effective ways to reduce oxidative stress as well as prevent livestock losses:
Polyphenol – potential attenuators of heat stress and oxidative stress in livestock
Polyphenols have attracted much attention in recent years due to their antioxidant ability and thus, are an effective attenuator of heat stress. As one of the critical secondary metabolic substances, polyphenols widely exist in a variety of plants and have been used for various purposes because of their strong antioxidant ability. Polyphenols can help activate the activity of stress-responsive proteins such as thermal shock proteins and antioxidant enzymes that can inhibit reactive oxygen species (ROS).
Nor-Grape 80 – Natural antioxidants from grape
Many research have evaluated antioxidant properties of many plants and found that grape byproducts are highly concentrated in polyphenols. Among different parts of grape, some research showed that the highest antioxidant capacity was found in grape seeds and skin, which contains bioactive and highly bioavailable, polyphenols such as antocyanins and proanthocyanidins.
Being extracted from an excellent source of natural antioxidants found in selected grape seeds and peels, known as possessing protective effects against oxidative stress, Nor-Grape engages significantly in the detoxification of Reactive oxygen species (ROS) and reinforces the animal defense system. Moreover, Nor Grape is able to regenerate and strengthen the activity of Vitamins like Vit E and Vit C, and increasing the production of endogeneous enzymes like Super Oxide Dismutase and Glutation Peroxidase, improving the animal resistance capacity against the Heat-Stress.
Stop heat app: a tool to optimize farm management, nutrition and antioxidant balance