Effects of Hydration Level and Heat Stress on Thermoregulatory Responses, Hematological and Blood Rheological Properties in Growing Pigs Xavier Waltz 1,2,3. , Michelle Baillot 2. , Philippe Connes 1,2,3,4 *, Bruno Bocage 5 , David Renaudeau 5,6 1 UMR Inserm 1134, Pointe-a `-Pitre, F-97159 Guadeloupe, Universite ´ des Antilles et de la Guyane, Pointe-a `-Pitre, France, 2 Laboratoire ACTES (EA 3596), De ´ partement de Physiologie, Universite ´ des Antilles et de la Guyane, Pointe-a `-Pitre, Guadeloupe, France, 3 Laboratory of Excellence GR-Ex, PRES Sorbonne Paris Cite ´ , Paris, France, 4 Institut Universitaire de France, Paris, France, 5 INRA, UR 143, Unite ´ de Recherches Zootechniques (URZ), Petit Bourg, France, 6 INRA, UMR 1348, Physiologie, Environnement et Ge ´ne ´tique pour l’Animal et les Syste `mes d’Elevage (PEGASE), Rennes, France Abstract Heat stress is one of the major limiting factors of production efficiency in the swine industry. The aims of the present study were 1) to observe if hemorheological and hematological parameters could be associated to physiological acclimation during the first days of heat stress exposure and 2) to determine if water restriction could modulate the effect of thermal heat stress on physiological, hematological and hemorheological parameters. Twelve Large White male pigs were divided into an ad libitum and a water restricted group. All pigs were submitted to one week at 24uC (D-7 to D-1). Then, at D0, temperature was progressively increased until 32uC and maintained during one week (D1 to D7). We performed daily measurements of water and feed intake. Physiological (i.e., skin temperature, rectal temperature, respiratory rate), hematological and hemorheological parameters were measured on D-6, D-5, D0, D1, D2 and D7. Water restriction had no effect on physiological, hematological and hemorheological parameters. The first days of heat stress caused an increase in the three physiological parameters followed by a reduction of these parameters suggesting a successful acclimation of pigs to heat stress. We showed an increase in hematocrit, red blood cell aggregation and red blood cell aggregation strength during heat stress. Further, we observed an important release of reticulocytes, an increase of red blood cell deformability and a reduction of feed intake and blood viscosity under heat stress. This study suggests that physiological acute adaptation to heat stress is accompanied by large hematological and hemorheological changes. Citation: Waltz X, Baillot M, Connes P, Bocage B, Renaudeau D (2014) Effects of Hydration Level and Heat Stress on Thermoregulatory Responses, Hematological and Blood Rheological Properties in Growing Pigs. PLoS ONE 9(7): e102537. doi:10.1371/journal.pone.0102537 Editor: Antonio Gonzalez-Bulnes, INIA, Spain Received March 7, 2014; Accepted June 15, 2014; Published July 11, 2014 Copyright: ß 2014 Waltz et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: The authors confirm that all data underlying the findings are fully available without restriction. All data are included within the paper. Funding: The present study has been funded by INRA (PigChange project 2012–2015). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * Email: pconnes@yahoo.fr . These authors contributed equally to this work. Introduction Heat stress is one of the major limiting factors of production efficiency in the swine industry by reducing voluntary feed intake with subsequent negative consequences on growth performance [1,2]. While thermal stress is an occasional problem in temperate areas during the 2–3 summer months, it is a chronic issue in many tropical countries where pig production has grown at a high rate during the last two decades [1]. Blood rheology is a key factor of blood flow and cardiovascular functioning [3,4] and hemorheological changes under heat stress could interfere with the physiological thermoregulatory adapta- tions [5]. We recently investigated the effect of heat stress on physiological, hematological, hemorheological parameters in different pig breeds [5]. In this experiment, three different pig breeds with assumed different heat stress tolerance were studied: Large White (little tolerance), Creole (good tolerance) and a cross between Large White and Creole breeds. Although red blood cell deformability was higher in Creole pigs exposed to heat stress compared to Large White pigs, the hematological and hemorheo- logical responses to heat stress were very similar [5]. However, in this previous study, the physiological, hematological and hemo- rheological parameters were measured after 5 days of heat stress exposure and pigs were probably acclimatized at that time. It was thus not possible to compare the ability of pigs to adapt to heat stress. To the best of our knowledge, the time for hematological and hemorheological parameters to normalize under heat exposure is unknown in pigs and might be connected to animal thermoregulatory responses. The aims of the present study were 1) to observe if hemorheological and hematological changes could be associated to physiological acclimation during the first days of heat stress exposure and 2) to determine if water restriction could modulate the effect of thermal heat stress on physiological, hematological and hemorheological parameters. We hypothesized that short- term physiological adaptation to heat stress could be accompanied by hematological and hemorheological changes. In addition, we hypothesized that the lack of changes in hematological and PLOS ONE | www.plosone.org 1 July 2014 | Volume 9 | Issue 7 | e102537