Answering Key Questions about Heat Stress in Pigs

Answering 8 questions

About heat stress

1

What is the economic cost of heat stress? Learn more

2

Which countries are most at risk for heat stress?

Why do pigs increase their water intake during heat stress?

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Why does heat stress affect gut integrity?

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5

3 What are the consequences of heat stress? Learn more

4

Why is a decrease in feed intake observed?

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KEY TAKEAWAYS:

6

What is the impact of heat stress on the energy metabolism of pigs?

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How can nutrition help decrease the impact of heat stress?

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7

8

• Heat stress is becoming more and more a topic in swine production as the temperatures are globally increasing which represents millions of losses for the swine industry annually

• Pigs adapt their behavior to better face heat stress by reducing their feed intake and consequently slowing their growth. Among other effects, gut functions are becoming secondary and less efficient

• Nutritional strategies including diet formulation as well as solutions that will help sustain the optimal gut integrity and functions are of great interest. LEVUCELL SB has shown beneficial results in this context

Bruno BERTAUD

Technical manager Yeast derivatives & Swine solutions

THE AUTHOR

What is the economic cost of heat stress?

It is difficult to accurately determine the global economic consequences of heat stress on pig production, especially because heat stress may impact sows, their offspring as well as the growth and the carcass composition of pigs. A study performed by Pollman in 2010 estimated the economic impact of heat stress on sows alone - taking into account only low sow performance - costs the U.S. swine industry $450 million annually.

Which countries are most at risk for heat stress?

Heat stress management is becoming more crucial each year mainly due to climate change, but also because pork production has increased in some location where the tropical and subtropical conditions are maximizing the negative impact of heat stress for the animals (Ross et al., 2015).

Time spent under heat stress and associated potential feed intake reduction (Lallemand Animal Nutrition, unpublished)

Physiologically, pigs are less tolerant to heat stress than other species of production animals (Cottrell et al., 2015). In pigs, one of the first visible signs of heat stress is a reduction in feed intake. Reducing nutrient intake during thermal pressure is a way the animal can reduce its own metabolic heat production from the digestion process (Baumgard and Rhoads, 2013). Countries that are known to undergo hot summer conditions are at risk for heat stress. Increasingly, heat stress is a concern for northern countries

- like the Netherlands, Germany, Ireland – and more - which are considered as temperate climates. This is not only about climate. Relative humidity should be considered. For instance, sows can suffer from heat stress even during temperatures lower than 25°C, and fattening pigs can undergo heat stress when the room temperature goes above 25°C. That makes properly designed animal housing and management critical to controlling heat stress.

Figure 1

What are the consequences of heat stress?

In addition to reducing feed intake, heat stress also impacts carcass composition, can modify insulin metabolism, compromises intestinal health - and reduces reproductive success (Liu et al., 2022). Reduced feed intake is the main driver of declines in growth performance. Nevertheless, it is also clear that heat stress induces a switch in the use of nutrients and, therefore can result in carcass compositions with more fat and less lean by reducing muscle deposition and increasing adipose tissue (Collin et al., 2001).

EXTERNAL VISIBLE SIGNS

• Increase respiration rate

• Bradycardia

• Increase body temperature

REPRODUCTION

Infertility: early pregnancy loss, semen and oocyte quality reduction, altered oestrus-toovulation interval

• Compromise intestinal barrier function

• Impact on microbiota composition

• Increase sensivity to diseases

• Increase mortality

Why is a decrease in feed intake observed?

It is well documented in the literature that the increase in ambient temperature is associated with a decrease in feed intake for pigs. Le Dividich et al. (1998) reported the decrease can be estimated at between 40 to 80g/°C/day, which is correlated with factors like the breed, body weight range, and the diet. The higher the temperature, the lower the feed intake will be. When exposed to heat, the ingestion time per day is reduced as well as the time per day spent in front of the feeding station (Quiniou et al., 2000).

During heat stress, reduced nutrient intake occurs to decrease metabolic heat production (Baumgard and Rhoads, 2013). This effect is particularly pronounced in recent years because of genetic selection for growth and carcass traits that have increased pig’s thermal sensitivity (Renaudeau et al., 2011).

METABOLISM

• Increase plasma insuline

• Impact carcass composition: more fat and less lean

• Increase water consumption

• Reduce feed intake

• Slow weight gain

Figure 2

General consequences of heat stress

Figure

Crude protein is the main responsible nutrient for metabolic heat production after a meal. Compared to starch or fat, heat increments due to metabolic utilization of digestible crude protein are significantly higher (Noblet et al., 1994). This is due to the deamination of the excess of amino acids for the urea synthesis (Renaudeau et al., 2008).

Why do pigs increase their water intake during heat stress?

Water plays a crucial role in the mechanism of heat exchange for temperature regulation and maintenance of hydric balance. In the case of heat stress, evaporation becomes the most important mechanism to evacuate heat. Indeed, high ambient temperatures increase water requirements for pigs. For example, when the ambient temperature increases from 20°C to 29°C, the sow’s water intake is multiplied by two moving from 4 to 8 L/kg of feed intake (Renaudeau et al., 2001). During respiration, water exchanges occur by evaporation from the body to the environment (called the latent heat loss route)

which helps reduce body temperature. This mechanism depends on the ambient temperature and relative humidity gradient. This process becomes quickly saturated even if pigs increase water consumption and, therefore, increase urinary water loss to disperse body heat (Renaudeau et al., 2008). The temperature of the water plays also a non negligeable role in the heat exchange mechanism efficacy. Supplying water at 15°C instead of 22°C to the sows improved performance of lactating sows and their piglets during heat stress events (Jeon et al., 2006).

Figure 4

Heat production variations linked to feeding activity and behavior (Serviento, 2022)

Under heat stress, pig reduce their activities to reduce heat production

Why does heat stress affect gut integrity?

During heat stress, there is a redirection of the blood stream to the skin’s surface to maximize the heat exchange by convection, conduction - and radiation (called sensible heat loss routes). The consequence of that is a vasoconstriction at the gastrointestinal tract level to redirect the blood flow towards peripheral circulation (Tang et al., 2022), which affects gut integrity of the epithelium (Lambert, 2009). The absorption of nutrients is therefore reduced, which also contributes to decreased growth performance and a reduction in feed intake.

• Weakened gut integrity and compromised gut barrier function

• Translocation of bacterial endotoxins into the blood circulation

• Activation of inflammatory responses

Figure

Redirection of bloodstream and associated consequences on gut barrier

Figure 6

Latent heat loss: respiration and evaporation to dissipate heat

Cui and Gu (2015) and Varasteh et al. (2015) described that heat stress weakens gut integrity and increases the epithelium’s permeability to pathogens and their toxins. This leads to an inflammatory response, cytokine production (including IL-6, IL-1beta and TNF-alpha) and - in more severe situations - leaky gut and diarrhea. Gabler et al. (2018) have also shown an increase by 50% of the circulating endotoxins due to the higher intestinal permeability of pigs exposed to heat stress, and the translocation of the pathogens can trigger systemic inflammation.

The inflammatory response is also responsible for a reduction of the energy expenditure for growth performance.

In addition to the inflammation, heat stress also reduces the standardized ileal digestibility of some amino acids like histidine (92.5-90%) or arginine (94-92%) as shown by Morales et al., 2016 but did not affect fat digestibility (Kellner et al., 2016). Therefore, growth performance and carcass composition of pigs exposed to heat stress will be affected.

What is the impact of heat stress on the energy metabolism of pigs?

Heat stress may affect carcass composition. Young pigs are generally less affected than heavier pigs (Christon, 1988), and it is quite clear that heat stress alters carcass composition with more fat and less lean (Close et al., 1971; Verstegen et al., 1978; Heath 1983, Bridges et al., 1998; Collin et al., 2001). This is due to a switch in the hierarchy of the normal nutrient utilization, which also leads to a reduction in growth performance (Ross et al., 2015).

Insulin also plays an important role in the thermal regulation of pigs exposed to heat stress (Baumgard and Rhoads, 2013). It has notably been shown that heat stress decreases insulin sensitivity (Yuen et al., 2013; Liu et al., 2017; Cottrell et al., 2019), which may induce - among other effects - changes in pigs’ feeding behavior. Pigs tend to reduce their feed intake as well as meal frequency when exposed to heat stress with negative consequences on growth performance.

DID YOU KNOW?

HEAT STRESS IMPACT ON MICROBIOTA

It is now well documented that the gut microbiota is strongly connected with the central nervous system and behavior by playing important physiological functions (Kraimi et al., 2019), called the gut microbiotabrain axis. Among other implications, the microbiota is involved in thermal heat acclimatization and fecal microbiota of growing pigs is affected by heat stress (Le Sciellour et a., 2019).

Insulin is a major regulator of metabolism and organ functions (Yee, L.D., 2020)

How can nutrition help decrease the impact of heat stress?

Strategies to reduce the negative impact of heat stress on pigs should be considered with a global approach including the management of the environment and especially the farm building (isolation, air temperature, cooling systems, etc.). The choice of genetics with lower sensitivities to heat stress as well as the nutritional strategies should also be considered. The feed plays a non negligeable role in the regulation of heat produced at the metabolic level. The Thermic Effect of Feeding (TEF) is a measure of how much the feed increases energy expenditure

– expressed as heat – due to the energy required to digest, absorb, and metabolize the nutrients. Pig diets are made up of three main categories of macronutrients: carbohydrates, proteins and fats. Each macronutrient goes through a different metabolic process to be broken down during the digestion process before absorption. Some of these metabolic processes are more efficient than others. The more efficient, the less energy in the form of heat is lost and therefore the less heat pigs will produce.

PROTEIN

DIETARY FIBER

Increased levels of dietary fiber generates heat due to fiber fermentation in the large intestine and reduces the bodyweight of sows exposed to heat stress (Renaudeau et al., 2003). Fat digestion and assimilation generates less heat production compared to protein or fiber. Formulating diets with an increased level of dietary fat and reduced levels of dietary protein and dietary fiber contributes to lower thermic effect of feeding diets.

ANTIOXIDANTS

Other nutritional strategies might be considered like the use of dietary antioxidants, chromium and/or betaine. Several authors (Rhoads et al., 2013; Montilla et al., 2013, 2014; Liu et al., 2015a) have demonstrated relationship between heat stress and oxidative stress in pigs. An imbalance between free radical production (Reactive Oxygen Species) and antioxidative capacity is observed in cases of heat stress and, in this context, dietary antioxidants help alleviate oxidative damage.

CHROMIUM

Chromium, added into the diet during summer periods, reduces the negative impact of heat stress (Hung et al., 2010, 2015). Chromium increases insulin sensitivity by increasing binding of insulin to cell receptors. Chromium supplementation also reduces plasma cortisol levels when animals are exposed to heat stress (Chang and Mowat, 1992; Samanta et al., 2008; Zha et al., 2009: Hung et al., 2014). Cortisol acts as an insulin antagonist. Reducing cortisol helps reduce glucose concentrations in the blood plasma and increases glucose utilization by peripheral tissues, which indicates a better insulin sensitivity.

BETAINE

Betaine is involved in osmotic regulation and plays an important role in several metabolic reactions. Among them, betaine can decrease the energy requirements for the pump mechanisms of cellular ions and leads to a whole-body energy savings of around 8% (Cronje, 2005) and a reduction of metabolic heat production.

GUT HEALTH STRATEGY

Other dietary strategies, acting on the gut integrity, must be considered as many of the negative consequences of heat stress affect the gut structure. By positively acting on the gut integrity, and also through several other mechanisms, Saccharomyces cerevisiae boulardii (CNCM I-1079) supplementation to pigs during heat stress has shown beneficial results in reducing its negative consequences.

LIVE YEAST IMPROVES PIGS RESILIENCE TO HEAT STRESS

HEAT STRESS, WHICH CONSEQUENCES?

A reduced feed intake is usually observed when pigs are exposed to heat stress during a long period of time. As they have a limited capacity to evacuate the heat, and due to the thermic effect of feeding, they modify their feeding behavior to limit their body heat production. Main physiological and metabolic consequences of heat stress are impaired intestinal barrier function, perturbations to the hormonal system, changes in thermoregulation responses...

The sensitivity of insulin, a key hormone involved in the regulation of multiple metabolic process such as the energy metabolism, may also be affected under heat stress.

SPECIFIC PROBIOTIC YEAST

LEVUCELL SB is the specific probiotic yeast Saccharomyces cerevisiae boulardii CNCM I-1079. More than 50 scientific publications in monogastric feeding have documented its beneficial effects on gut health.

Under heat stress conditions, LEVUCELL SB helps maintain optimal gut barrier integrity functions and reduces the risk of pathogen endotoxin translocation into the blood stream with associated inflammation.

Supplemented pigs with LEVUCELL SB better cope with heat stress. Lactation performance are improved, and fattening pigs are more efficient converting feed into growth.

Maintenance of healthy gut functions

Metabolic response adaptations

Insulin sensitivity

OVERALL BETTER ADAPTATION TO HEAT STRESS

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