Immune system stimulation of growing pigs does not alter apparent ileal amino acid digestibility but reduces the ratio between whole body nitrogen and sulfur retention ☆ A. Rakhshandeh a , J.K. Htoo b , C.F.M. de Lange a, ⁎ a Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario Canada N1G 2W1 b Evonik Degussa Canada Inc., Gibbons, Alberta Canada T0A 1N0 article info abstract Immune system stimulation (ISS) can cause morphological and physiological changes in the gastrointestinal tract and impact nutrient utilization in pigs. Apparent ileal digestibility (AID) of sulfur amino acids (SAA) and whole body nitrogen (N) to sulfur (S) balance ratios (N/S-balance) were measured to investigate the impact of ISS and SAA intake on SAA digestibility and utilization in growing pigs. Thirty-six barrows (initial BW 21.5 ± 3.5 kg) were fed 800 g/day of SAA-limiting diets that supplied 1.1, 2.1 or 3.2 g/day of SAA (L1, L2 and L3, respectively). Following adaptation, pigs were injected intramuscularly, with either saline (ISS-; 4 pigs at each SAA intake level) or increasing amounts of Escherichia coli lipopolysaccharide (LPS) (ISS+; 8 pigs at each SAA intake level), while measuring whole body N and S balances. At the end of the balance period, pigs were euthanized and digesta were collected from the distal 1.5 m of small intestine for measuring AID (%) of amino acids and energy. The AID of energy and amino acids were not affected by ISS. Whole body N and S retention increased with SAA intake (P b 0.01), while only N retention was reduced by ISS (P b 0.05). Whole body N/S-balance was reduced as SAA intake decreased; ISS further reduced the N/S-balance (P b 0.03), indicating an increase in whole body non-protein SAA pool size due to ISS. In conclusion, ISS per se does not change the AID of amino acids and energy but alters the partitioning of SAA in favor of non-protein body stores in growing pigs. © 2010 Elsevier B.V. All rights reserved. Keywords: Apparent ileal digestibility Sulfur amino acids Immune system stimulation N-balance S-balance Pigs 1. Introduction The gastrointestinal tract is involved in defense activities during immune system stimulation (ISS). This involvement results in morphological and physiological changes in intestinal tissue (Hang et al., 2007; Faure et al., 2007). However, little is known about the impact of ISS on measures of nutrient digestibility. The end-products of sulfur amino acid (SAA) catabo- lism, taurine, sulfate and ester sulfate are mainly excreted in the urine (Stipanuk, 1999). Therefore, urinary sulfur (S) excretion provides a measure of SAA catabolism. A distinguishing characteristic of SAA is the considerable storage of cysteine in non-protein pools, e.g. glutathione (GSH). GSH has lower nitrogen (N) to S ratio than body protein (Cho et al., 1981). Therefore, changes in the whole body N to S-balance ratio (N/S-balance) could indicate changes in non-protein SAA pool size with changes in metabolic status (Hou et al., 2003). Our objectives were to determine the impact of ISS on apparent ileal digestibility (AID) of nutrients and whole body N and S retention in growing pigs fed SAA-limiting diets. 2. Material and methods Thirty-six barrows (BW 21.5±3.5 kg) were fed 800 g/d of one of three semi-synthetic diets that were formulated Livestock Science 134 (2010) 21–23 ☆ This paper is part of the special issue entitled “11th International Symposium on Digestive Physiology of Pigs”. ⁎ Corresponding author. Tel.: +1 519 824 4120; fax: +1 519 836 9873. E-mail address: cdelange@uoguelph.ca (C.F.M. de Lange). 1871-1413/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2010.06.085 Contents lists available at ScienceDirect Livestock Science journal homepage: www.elsevier.com/locate/livsci