The aim should be to reduce the thermoregulatory effort for pigs, so that they can recover quickly after acute heat stress.


In growing pigs, similar inter-individual variability was also established.


Specific feed formulations In homeothermic animals, reduced metabolic heat production under heat stress conditions is an adaptation that helps to regulate the internal body temperature regardless of external influence. One third of the heat produced by the pig is due to the digestive and metabolic use of nutrients, so called the thermic effect of feed (TEF). This dietary characteristic can be assessed through the ratio between the net energy and metabolisable energy concentrations (NE/ME ratio). With regard to production of metabolic heat, a decrease in daily feed intake from 2.50 to 2.23 kg can be theoretically compensated through the increase in dietary NE content from 9.7 to 10.9 MJ/kg. Formulation of low TEF diets is usually achieved with a decreased value of the constraint applied to the maximum crude protein concentration (but for similar constraints in minimum concentration in essential amino acids), fat and fibres. Many research teams focus their investigations on the incorporation of specific additives (antioxidant molecules, functional amino acids/peptides, live yeasts, sodium bicarbonate…) in order to cover the specific need due to the thermoregulation efforts. However, up until recently these kinds of formulation have been mainly used in warm climates such as Asia and Australia. In Europe, they are used sometimes at the beginning of the warm season, to reduce the impact of a chronic heat stress on performance, mainly in lactating sows. In practice, it is difficult to switch from one diet to another in a reactive way based on feed delivery systems currently installed in commercial pig farms. But new equipment, such as electronic feed dispensers developed with two or three hoppers could help to modulate the quality of the diet delivered in a very reactive way.


Long-term effects on animal performance Recently, it has been shown that summer heat waves have short and long-term effects on animal performance. That includes a strong reduction in voluntary feed intake during the acute heat stress event (with subsequent effects on digestive physiology and growth) and thereafter a lack of compensatory responses to heat stress induced feeding restriction. In addition, both the dynamic of the physiological response and the sensitivity to temperature differ among individuals. An inter-individual variability has been observed for example in primiparous sows. Under high ambient temperature, daily feed intake and milk production remain very high for some of them whereas they decrease for others. Subsequently the risk of being culled is higher after weaning for these animals, while less sensitive sows are more likely to be kept longer in the herd.


Adjusted feed delivery A different partition of feed intake is expected to attenuate the impact of high ambient temperature. Trials performed in respiratory chambers at the experimental station INRAE (Saint-Gilles, Brittany, France) provided some information about the dynamics of heat production, especially heat released after a feed. The bigger the meal is, the more important the heat to be released is. However, the heat is not immediately released after the feed. Due to the metabolic process involved in the digestion and the physiological use of the energy intake, the short-term thermic effect of the diet is observed over the few hours following a feed (Figure 2). Then again after a feed, taken 1 hour before the time when the ambient temperature peaks above thermoneutral conditions, the amount of heat to be released is still important. The situation the animal faced was all the more difficult as the feed was spontaneously large. Difficulty losing heat under such conditions may have


▶ HEAT STRESS | MAY 2021 21


PHOTO: IFIP


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60