Effects of heat stress on feeding behavior and energy metabolism of pigs submitted to an inflammatory challenge

Inflammatory response in mammals is known to be interfered by heat stress. The aim of this study is to evaluate the metabolic response of pigs to an inflammatory challenge when housed on heat stress conditions. Two pairs of growing pigs (approx. 50 kg BW; females), Pietrain x (Large White x Landrace) were exposed to conditions of thermo-neutrality (TN) at 24 degrees C or heat stress conditions (HT) 30 degrees C after acclimatization, during two consecutive periods: a first period (P1; 7 days) in which animals were not immunologically stimulated, and a second period (P2, 10 days) where E. Coli lipopolysaccharide (LPS) was injected every 48 hours in order to induce an inflammatory reaction. Animals were housed in two identical respiration chambers (one chamber in TN and the other in HT). The feed intake, weight, the components of the heat production (HP, measured by indirect calorimetry in the respiration chambers), feed digestibility, energy balance, nitrogen, water consumption and internal temperature were measured at 4 pigs, 2 per environmental condition in a total of eight replicates. There was a reduction in average daily feed intake (ADFI) due to the effect of temperature (P less than 0.01) and period (P equal to 0.02). Heat production (HP) was also affected by temperature (P less than 0.01) and period (P less than 0.01). There were changes in metabolic energy requirements for maintenance (MEm), affected by temperature (P less than 0.01) and period (P less than 0.01; 1139 TN kJ per BW0.60 per day in TN,P1; 1092 kJ per BW0.60 per day in TN,P2; 1013 HT kJ per BW0.60 per day in HT,P1; and 980 kJ per BW0.60 per day in HT,P2). The metabolized energy intake (ME intake) reduction caused a decrease in the energy retained (519 TN kJ per BW0.60 per day in TN,P; 233 kJ per BW0.60 per day in TN,P2; 264 HT kJ per BW0.60 per day in HT,P1; and 160 kJ per BW0.60 per day in HT,P2) which affected the deposition of protein (292 g per d in TN, P1; 133 g per d in HT, P2) and lipids (148 g per d in TN, P1; 23 g per d in HT, P2). Amino acids were used as energy source due to the energy shortage, the ratio Nretained per Ndigestible got affected. On the one hand feed efficiency was reduced due to stress factors, and secondly due to differences between the requirements and the nutrient supply. Thus, recommendations to adjust diets to the needs in stress situations may be useful to improve to improve the response of animals and to optimize the feed efficiency.