Gut integrity is affected by heat stress HS can lead to functional disorders, inflammation, and an increased risk of infections of the digestive tract. Research has shown that HS compromises intestinal integrity, triggering increased levels of cortisol (corticosterone), pro-inflammatory cytokines and reactive oxidative species (ROS), hence resulting in inadequate levels of nutrient uptake, poor performance, suboptimal overall health, and mortality. Therefore, minimising the negative impact of heat stress on an intestinal level is an important approach to maintain produc- tivity and health of farm animals. There are several nutritional interventions available, e.g. the use of feed ingredients with high digestibility, optimal amino acid balance and low heat in- crement. Furthermore, specific bioactive compounds have shown positive effects supporting the animal under HS condi- tions, including electrolytes, vitamins, antioxidants and select- ed plant-derived compounds (e.g. betaine, plant extracts). There is an increasing body of evidence indicating that botani- cal bioactive compounds have the potential to alleviate HS-induced losses in performance and livability. Since the quantification of the impact of HS is challenging, con- trolled experiments are necessary to evaluate the potential of nutritional solutions in HS challenge trials. A recent study investigated the impact of specific botanical compounds (isoquinoline alkaloids, IQs) in broilers undergoing controlled HS. The study confirmed that HS significantly re- duced feed intake (-20%), growth rate (BW -20%) and feed effi- ciency (FCR +6%) (data not shown). However, supplementation with botanical IQs increased performance of the heat stressed birds (Figure 1a,b). Broilers were better able to cope with the impact of HS. Levels of corticosterone, the major glucocorticoid involved in the stress response of birds, and the pro-inflamma- tory cytokine interleukin-6 were down-regulated compared to the HS-Control. Furthermore, reduced levels of FITC-dextran in the blood indicated enhanced gut integrity. FITC-dextran is a suitable marker for gut integrity as the transfer of this com- pound from the intestine into the blood is usually limited and increases in case of enhanced paracellular gut permeability. Pigs are also highly susceptible to HS. Like in other species,
the consequences of HS in pigs include (1) reduced feed in- take in order for the animal to reduce the generation of meta- bolic heat, (2) increased blood flow to the body periphery to facilitate radiant heat loss, and (3) accelerated respiration rate to increase evaporative heat loss. In a study with grower pigs Le et al. (2020) found that supplementation with botanical IQs ameliorated the consequences of HS and helped to pro- tect the animals against HS-induced increases in intestinal permeability in the colon. Respiration rate and body temper- ature were lower in pigs fed supplemented diets (Figure 2). These controlled experiments demonstrate the potential of dietary strategies to assist pigs and poultry in coping with the consequences of HS.
New nutritional solutions Poor growth performance and health associated with heat stress are mediated by a decline in gut integrity. New nutrition- al solutions including specific botanical compounds help to al- leviate the negative impact of heat stress on the intestinal bar- rier. Such strategies can be implemented to reduce production losses and to support productivity during hot seasons.
References are available on request
Figure 2 - Respiration rate, rectal and skin temperature in pigs (LW 32.7 kg) exposed to heat stress with or without supplementation of betaine or botanical compounds. Respiration rate
190 170
150 130 110 90 70 50
* *
39.5 39
38.5 38
Control Bet IQs Control Bet IQs *
Rectal temperature 40.5
40 *
39.5 39
38.5 38
Control Bet
Adapted from Le et al. (2020) *significant difference vs. Control (p < 0.05). HS = 35° from 9 am-5 pm and 28° from 5 pm-9 am.
▶ HEAT STRESS | MAY 2021 47 IQs 40.5 40 * *
There are many parameters to determine the impact of HS. For example feed and water intake, panting score and FCR.
Skin temperature
Breaths/minute
°C
°C
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