Avoid losing money during heat waves due to loss of performance and health issues

1. Consequences of heat stress in ruminants

Unlike other animals, cattle have great difficulty in dissipating their heat loads efficiently, as they do not sweat much and rely on respiration to cool down.

Moreover, the fermentation processes that take place in the rumen generate additional heat that the animal has to dissipate. Heat stress refers to the inability of the body to maintain a normal temperature under conditions of high temperature and humidity. An unbalance occurs between the metabolic heat produced inside an animal’s body and its dissipation to the surroundings. Animals increase their respiratory rate and consume energy to dissipate excess heat, which contributes to a significant increase in their maintenance requirements. Heat stress can be evaluated through the Temperature Humidity Index (THI). The higher the THI is, the more cattle need to fight the heat.

Heat stress is one of the main challenges that livestock farmers face. Indeed, over the last quarter of a century, cows, as well as other livestock, have mainly been selected on the basis of their productivity and not for their thermotolerance or climate adaptation capacity. As a result, animals have evolved to be highly productive but also particularly sensitive to environmental variations and hot conditions. Furthermore, in the context of global warming, which is accompanied by an increase in the frequency of heat waves, exposure to heat stress is becoming increasingly common and is likely to intensify in the coming years.

Visible signs of heat stress result from the physiological and metabolic responses of an animal to heat stress as shown in Figure 1. The harmful effects of heat stress are due to these responses and to the animal’s efforts to re-establish body homeostasis. In particular, these responses cause oxidative stress, which compromises the health status of animals and leads to immunosuppression, as well as a drop in production and reproductive performance.

Figure 1: Physiological and metabolic responses to heat stress (Gonzales-Rivas et al, 2020)

2. Economic losses due to heat stress

Heat stress causes significant economic losses on livestock farms due to various factors including a drop in milk production, slower growth rates, lower fertility, increased veterinary costs and lower milk quality, all of which result in increased costs and reduced profits which lower margins for producers.

St-Pierre et al. (2003) developed a model that can be used to calculate the economic losses due to heat stress by taking into account the effects of heat stress on dry matter intake, milk production, reproduction, culling, and death of both young stock and adult cows. They estimated that US $2.4 billion is lost annually in livestock production due to heat stress, with losses by the dairy industry accounting for roughly US $900 million. Adding to this are the veterinary costs associated with the increased incidence of mastitis and acidosis due to heat stress. These losses can be as high as several hundred dollars per dairy cow per year.

Furthermore, as global temperatures rise, and heat waves become more frequent, higher economic losses from heat stress can be expected. Investments in heat abatement systems and more effective nutritional and long-term solutions to combat the harmful effects of heat stress are therefore needed to cope with this present and future challenge. A study has been conducted to investigate the cost-effectiveness of heat abatement strategies during the 21st century using climate projections. It has shown that intense heat stress abatement strategies (e.g., with air conditioning) in the mid-21st century would reduce the costs by -US $30 to US $190 /dairy cow and -US $20 to US $590 /dairy cow in late 21st century (Gunn et al., 2019).

3. Limit heat stress through nutritional management

Nutritional management is an effective tool to manage heat stress when used in complement with rearing practices such as:

• Adapting the rhythm of the day to the heat
• Optimize water access
• Adjusting the feed
• Avoiding other sources of stress
• Increasing the airflow around the animals
• Using sprinklers
• Decreasing fly populations
• Maximizing shade

3.1 The importance of selenium supplementation

To counteract the effect of heat stress, an animal’s antioxidant defense mechanism works by scavenging free radicals, detoxifying the products of their metabolism, and repairing damaged molecules (Figure 2). These systems are based on the synthesis of biological antioxidants, including antioxidant enzymes, glutathione, thioredoxin and coenzyme Q. The main players in the antioxidant system are vitamin E, vitamin C, carotenoids, polyphenolics, and Se (through antioxidant enzymes such as glutathione peroxidase, and the thioredoxin system). Dietary supplementation with those antioxidants helps support the animal’s antioxidant defense, thereby improving the animal’s health status and maintaining its performance.

Figure 2: Antioxidant defense mechanisms in the body (Surai et al, 2019)

Animals supplemented with Selenium (Se) are more resistant to oxidative stress and maintain their performance and their general state of health. Indeed, Se plays a pivotal role within the antioxidant system (Figure 3); it is a key component of two amino acids, selenomethionine (SeMet) and selenocysteine (SeCys). The natural storage form of selenium is
SeMet, while SeCys is the active form found at the catalytic site of selenoproteins. Currently, 25 selenoproteins have been identified in animal tissues and more than half of them are directly or indirectly involved in the maintenance of the body’s redox balance and antioxidant defense (e.g., glutathione peroxidase). Selenoproteins are also involved in thyroid metabolism, spermatozoa function, as well as inflammatory and immune responses.

Bioavailability of Se depends on the form of dietary Se that is offered to the animal. Selenium additives can be divided into two main families:

• inorganic sources, such as sodium selenite (SS), selenate, proteinate and glycinate (which are SS-based products);
• organic sources, including seleno-yeasts (SY) – which provide on average 60% of Se as SeMet -and the pure forms of organic Se – providing 100% of Se as SeMet or OH-SeMet (Selisseo® 2%).

The main advantage of feeding SeMet to animals is that the dietary SeMet is stored in body tissues in advance of a stressful episode. This allows the creation of a reservoir of Se that the animal can utilize when stress levels increase and the intake of nutrients, Se and of other antioxidants decrease. This feature allows the animals to maintain selenoprotein synthesis even during stressful situations and to help them to cope better with heat stress and to maintain better performance.

Figure 3: Selenium the chief-executive of the antioxidant system

Read more on the effect of Selisseo® in dairy cows

3.2 Amino acid balancing through protected methionine supplementation

Methionine is an essential nutrient that was known first for its effect on the production of milk, milk protein, and milk fat during lactation. Its impacts on health and reproduction pre- and post-calving have been established more recently. Now research is defining how methionine minimizes the negative impact of heat stress.

“The number of dairy nutritionists routinely balancing the amino acid levels in dairy rations for pre-fresh and lactating cows continues to climb. By answering the cow’s needs for methionine, the production of milk and components, health status at transition, and reproductive efficiency can each increase,” says Dr. Brian Sloan, Business Director – Protected Amino Acids, Adisseo.

Research at Nanjing Agricultural University in China showed that dairy cows challenged to temperatures up to 36°C (96.8°F) displayed blood biomarker levels typical of heat stress. Providing methionine, typically the first-limiting amino acid, to amino acid balance the rations stabilized the heat stress markers. This suggests that balancing rations by adding methionine helps counteract heat stress in cows.

Table 1: Biomarker levels of animals under heat stress conditions supplemented with MetaSmart® Dry

Research at the University of Illinois looked at the effect of heat stress on lactation performance when cows were fed with supplemental methionine as Smartamine® M, or without rumen-protected methionine (Control). Heat stress had a significant negative effect on milk protein and milk fat content, whereas supplemental methionine significantly improved milk protein and milk fat content during heat stress (Pate et al., 2020).

Figure 4: Change in Component Concentration ± Supplemental Methionine during a heat stress challenge

Further research into the role of methionine as a functional nutrient at the University of Illinois showed how fully meeting the methionine needs of lactating cows mitigates the impact of heat stress. Amino acid balancing with additional methionine provides dairy cows with the capacity to modulate mRNA and the protein abundance of genes and proteins related to metabolism, immune responses, and antioxidant systems, making the cows more resilient to the impact of heat stress (Coleman et al., 2022a and b).

“Being proactive in preparing cows for optimal performance during heat stress is good herd management. It enables cows to perform better during and after heat stress,” Dr. Sloan says.

Ongoing research will further define the methionine requirement of dairy cows and allow us to maximize her ability to perform at her best during heat stress.

Conclusion

The metabolic and physiological responses of an animal under heat stress have negative impacts on its performance, in terms of production and reproduction, and alter its general state of health. It is an annual problem, and it will surely get worse due to global warming. The economic consequences are and will become more serious for livestock farms. However, there are solutions available to limit the harmful effects of heat stress. Feeds in particular are a major lever of action. Supplementing animals with antioxidants and amino acid balancing rations are effective ways to fight and mitigate effects of heat stress.

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