HEAT STRESS ▶▶▶


Amino acids to overcome heat stress problems


Grower pigs can feel the negative effects of heat stress in various ways. To overcome this, a nutritional strategy of lowering crude protein levels and stepping up the amino acid levels can help. The type of amino acids, however, makes all the difference.


BY DR ING JOHN HTOO, DIRECTOR TECHNICAL CONSULTANCY – SWINE, EVONIK P Water intake


igs exposed to an ambient temperature of 31°C or more show signs of heat stress, making it one of the biggest challenges for pig production in many countries. Pigs are sensitive to heat, and under heat


stress they typically reduce voluntary feed intake by 20–40% to reduce heat production and maintain thermal homeosta- sis. Lowering feed intake directly reduces nutrient intake and availability for the pigs. Under heat stress, pigs also have in- creased blood flow to the external surface, such as the face and neck, to dissipate heat. However, this reduces oxygen and nutrient supply to the internal organs, causing impaired gut integrity. Heat stress exposure can also lead to oxidative stress, caus- ing cell membrane damage associated with increased use of amino acids for antioxidant function, which then reduces


Figure 1 - Impact of heat stress on digestive physiology, nutrient supply and growth of pigs.


Heat stress Body temperature


O2 & nutrients to internal organs


(blood redirection) Feed intake Intestinal integrity Nutrient intake


Altered Intestinal physiology


Nutrient absorption and availability


12 Growth performance


amino acids available for growth. All these factors cause a re- duction in pig performance, resulting in economic losses for swine production (see Figure 1). As well as adequate farm management (ventilation, stocking density; cooling, water intake), nutritional strategies (low protein diets and feed additives) can mitigate the negative effects of heat stress in pigs. Researchers at Evonik conducted two experiments in collab- oration with the Universidad Autónoma de Baja California in Mexicali, Mexico, to determine the effect of dietary level and whether the form of amino acids affects nutrient utilisation and growth of heat-stressed pigs.


Oxidative stress (ROS production)


Cell membrane damage


AA need for antioxidant function


AA availability for growth


Trial results: Experiment 1 In experiment 1, to determine the effect of heat stress on the performance of pigs fed high or low crude protein diet, pigs of roughly 31 kg were assigned to three treatments for 21 days. • Treatment 1 was a 22% high crude protein (CP) diet based on wheat, soybean meal and canola oil (without supplemental amino acids) but adequate in all amino acids (standardised ile- al digestible [SID] lysine of 0.98%) according to the National Research Council (2012). Pigs were kept under thermoneutral conditions with ambient temperatures of 20–24°C. • Treatment 2 was the same as treatment 1, but pigs were kept in heat stress conditions with ambient temperatures in the range 25–43°C. • Treatment 3 was a 14% low CP diet based on wheat, soy- bean meal and nine supplemental amino acids, and adequate in all amino acids (0.98% SID lysine), but pigs were kept under heat stress conditions. The main results of experiment 1 are shown in Figure 2. Com- pared with pigs kept in thermoneutral conditions, exposure to heat stress reduced feed intake and average daily gain (ADG) of pigs fed both high CP and low CP diets. Under heat stress, reducing dietary CP from 22% to 14% significantly im- proved gain:feed (G:F) efficiency, which was similar to pigs kept under thermoneutral conditions.


Trial results: Experiment 2 A simple approach to counteract reduced amino acids intake due to low feed intake is to supply more amino acids in the diet. As such, the aim of experiment 2 was to determine the effect of extra amino acid supply from protein-bound or free


▶ PIG PROGRESS | Volume 37, No. 5/6, 2021


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