239. Heat Stress Alters Gastrointestinal Motility and Digestive Parameters in Finishing Pigs.

Abstract

Heat stress is a major challenge in livestock production, particularly in pigs. High-performance hybrids in the finishing phase are highly sensitive to elevated temperatures, which may compromise productivity, gut health and welfare. Heat stress triggers endocrine and metabolic responses that may impair gastrointestinal function and nutrient utilization. This study aimed to characterize changes in gastrointestinal motility and digesta parameters in finishing pigs during heat stress and the recovery period. In a controlled experiment, 18 PVTC-cannulated finishing pigs (DanBred × Large White × DanBred × Landrace; 86.4 ± 4.0 kg) were first maintained under thermoneutral conditions, followed by a 12-d heat stress period and a 4-d reacclimatization phase. Ambient temperature was 32 °C/26 °C (day/night) during heat stress and 20 °C under thermoneutral conditions. Smooth muscle electromyographic (EMG) activity of the small and large intestine was recorded continuously using skin surface electrodes, quantified every 30 min as Power Spectrum Maximum. Measurements were performed during the thermoneutral phase (TN, n = 5), on days 6 (short heat stress, SHS, n = 3) and 11 of the heat stress period (long heat stress, LHS, n = 3), and on day 3 of the reacclimatization period (RTN, n = 3). Fecal samples were collected on the same days as EMG recordings; ileal chyme samples were obtained at TN (7 d before heat stress), on days 7 and 12 of heat stress, and on day 4 of the recovery phase to measure chyme pH and viscosity. Data were analyzed using linear mixed-effects models with phase (TN, SHS, LHS, RTN) and time (within the day) as fixed effects and individual as a random effect; pairwise comparisons were performed using Tukey-adjusted post-hoc tests (P < 0.05). EMG recordings revealed gastrointestinal activity alterations across experimental phases. Compared with TN, small intestinal activity decreased during SHS (P = 0.043), remained unchanged during LHS (P = 0.76), and increased during RTN (P < 0.001), indicating a hypercompensatory response. Temporal patterns differed among phases (Phase × Time, P = 0.015; Phase × Time², P < 0.001). Large intestinal activity showed circadian variation with significant effects of time (P < 0.001) and phase–time interactions (P < 0.05). Large intestinal activity increased during SHS but declined during LHS, suggesting altered transit dynamics. Relative to TN conditions, activity was higher during SHS (P = 0.0005), LHS (P = 0.0197), and RTN (P < 0.001). Ileal digesta pH increased progressively from TN (5.05 ± 0.10) to SHS (5.55 ± 0.10), LHS (5.86 ± 0.11), and RTN (5.96 ± 0.11; all P < 0.05), whereas digesta viscosity remained unchanged among phases. Fecal dry matter content decreased in all heat stress and reacclimatization phases compared with TN (37.4 ± 0.7%, P < 0.001). Results demonstrate organ-specific gastrointestinal responses to heat stress in finishing pigs. These alterations may be considered when developing nutritional strategies to mitigate the negative effects of heat stress.