The impact of immune system stimulation (ISS) on the ileal nutrient digestibility and utilisation of dietary methionine plus cysteine (SAA) intake for whole-body protein deposition (PD) was evaluated in growing pigs. For this purpose, sixty barrows were used in two experiments: thirty-six pigs in Expt I and twenty-four pigs in Expt II. Pigs were feed restricted and assigned to five levels of dietary SAA allowance (three and two levels in Expt I and II, respectively) from SAA-limiting diets. Following adaptation, pigs at each dietary SAA level were injected with either increasing amounts of Escherichia coli lipopolysaccharide (ISSþ; eight and six pigs per dietary SAA level in Expt I and II, respectively) or saline (ISS2; four and six pigs in Expt I and II, respectively) while measuring the whole-body nitrogen (N) balance. After N-balance observations, pigs were euthanised, organs were removed and ileal digesta were collected for determining nutrient digestibility. Ileal digestibility of gross energy, crude protein and amino acids was not affected by ISS (P.0·20). ISS reduced PD at all levels of dietary SAA intake (P, 0·01). The linear relationship between daily dietary SAA intake and PD observed at the three lowest dietary SAA intake levels indicated that ISS increased extrapolated maintenance SAA requirements (P,0·05), but had no effect on the partial efficiency of the utilisation of dietary SAA intake for PD (P. 0·20). Physiological and metabolic changes associated with systemic ISS had no effect on the ileal digestibility of nutrients per se, but altered SAA requirements for PD in growing pigs.

Two experiments (EXPs) were conducted to evaluate models of immune system stimulation (ISS) that can be used in nutrient metabolism studies in growing pigs. In EXP I, the pig's immune response to three non-pathogenic immunogens was evaluated, whereas in EXP II the pig's more general response to one of the immunogens was contrasted with observations on non-ISS pigs. In EXP I, nine growing barrows were fitted with a jugular catheter, and after recovery assigned to one of three treatments. Three immunogens were tested during a 10-day ISS period: (i) repeated injection of increasing amounts of Escherichia coli lipopolysaccharide (LPS); (ii) repeated subcutaneous injection of turpentine (TURP); and (iii) feeding grains naturally contaminated with mycotoxins (MYCO). In EXP II, 36 growing barrows were injected repeatedly with either saline (n 5 12) or increasing amounts of LPS (n 5 24) for 7 days (initial dose 60 mg/kg body weight). Treating pigs with TURP and LPS reduced feed intake (P , 0.02), whereas feed intake was not reduced in pigs on MYCO. Average daily gain (ADG; kg/day) of pigs on LPS (0.50) was higher than that of pigs on TURP (0.19), but lower than that of pigs on MYCO (0.61; P , 0.01). Body temperature was elevated in pigs on LPS and TURP, by 0.88C and 0.78C, respectively, relative to pre-ISS challenge values (39.38C; P , 0.02), but remained unchanged in pigs on MYCO. Plasma concentrations of interleukin-1b were increased in pigs treated with LPS and TURP (56% and 55%, respectively, relative to 22.3 pg/ml for pre-ISS; P , 0.01), but not in MYCO-treated pigs. Plasma cortisol concentrations remained unchanged for pigs on MYCO and TURP, but were reduced in LPS-treated pigs (30% relative to 29.8 ng/ml for pre-ISS; P , 0.05). Red blood cell glutathione concentrations were lower in TURP-treated pigs (13% relative to 1.38 mM for pre-ISS; P , 0.05), but were unaffected in pigs on LPS and MYCO. In EXP I, TURP caused severe responses including skin ulceration and substantial reductions in feed intake and ADG, whereas MYCO did not induce effective ISS. In EXP II, ISS increased relative organ weights, eye temperature, white blood cell count and plasma acute-phase proteins (P , 0.05), confirming that repeated injection with increasing amounts of LPS induced chronic and relatively mild ISS. Repeated injection with increasing amounts of LPS is a suitable model for studying nutrient metabolism and evaluating the efficacy of nutritional intervention during chronic ISS in growing pigs.

Chronic subclinical levels of disease occur frequently in intensive swine production and compromise nutrient use efficiency. Feeding additional Met plus Cys (M+C) has been implicated in improving the response of the animal to immune system stimulation (ISS) because they can serve as substrates for generating compounds involved in the immune response, such as glutathione and acute phase proteins. A N-balance study was conducted to assess the optimal dietary Met to Met plus Cys ratio (M:M+C) during ISS in 20-kg pigs. Thirty-six pigs were fed 800 g/d of 1 of 5 M+C-limiting diets, containing graded levels of M:M+C (0.42, 0.47, 0.52, 0.57, and 0.62) and supplying 2.5 g/d of M+C. After adaptation, N balances were determined sequentially during a 5-d prechallenge period and 2 ISS periods of 3 and 4 d, respectively. To induce ISS, pigs were injected intramuscularly with repeated and increasing doses of Escherichia coli lipopolysaccharide. Eye temperature and blood profile confirmed effective ISS. During ISS period 1, ISS reduced the mean N balance more severely than ISS period 2 (8.7 ± 0.3 vs. 9.6 ± 0.4 g/d; P < 0.001) and was less than the prechallenge period (10.0 ± 0.2 g/d; P < 0.001). An interactive effect of ISS and diet on N balance was observed (P < 0.001). Based on quadratic-plateau regression analysis, the optimal dietary M:M+C was 0.57 ± 0.03 and 0.59 ± 0.02 for the prechallenge period and ISS period 2, respectively. The optimal dietary M:M+C for ISS period 1 was found to be greater than 0.62, indicating that the optimal M:M+C is greater during ISS. It is suggested that this is the result of preferential use of Met during ISS. In conclusion, ISS results in an increase in the optimal dietary M:M+C in growing pigs.

Rakhshandeh, A.; Weber, Thomas E.; Dekkers, Jack C. M.; Kerr, Brian J.; English, J.; and Gabler, Nicholas K., "Effect of immune system stimulation and divergent selection for residual feed intake on digestive capacity of the small intestine in growing pigs" (2012).