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

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 < 0.01), while only N retention was reduced by ISS ( P < 0.05). Whole body N/S-balance was reduced as SAA intake decreased; ISS further reduced the N/S-balance ( P < 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.