Additional dietary tryptophan and methionine improves feed conversion efficiency and markers of inflammation in weaner pigs infected with Escherichia coli

Activation of the innate immune system after weaning leading to inflammation of the gastrointestinal tract (GIT) has been linked to compromised GIT barrier function, increased risk of enteric disorders, and poorer performance (Gallois et al. 2009). To counteract these effects, the dietary requirement for some amino acids such as tryptophan (Trp) and (or) sulphur amino acids (SAA) may increase. The present experiment tested the hypothesis that additional dietary Trp and (or) SAA would improve growth performance and ameliorate indicators of inflammation in weaner pigs experimentally infected with Escherichia coli.

Male pigs (n = 76) (Landrace × Large White) with an initial body weight (BW) of 6.2 ± 0.78 kg (mean ± SD) were stratified into one of four treatments according to a 2 × 2 factorial arrangement, with the factors being ratios of: 0.16 or 0.24 standardised ileal digestible (SID) Trp:Lysine (Lys); and 0.52 or 0.60 SID SAA:Lys (using SID coefficients from Sauvant et al. 2004). Diets were formulated to contain 11.2 MJ net energy/kg, 14 g SID Lys/kg and 198 g/kg crude protein, and were fed to pigs in meal form ad libitum for 2 weeks after weaning. Pigs were infected with 6, 8 and 10 mL of an enterotoxigenic strain of E. coli (3.44 × 10⁸ colony forming units/mL; serotype O149:K98:K88; toxins LT, ST, and STb) on d 5, 6 and 7 after weaning, respectively. Blood samples were taken on d 8 after weaning and measured for C-reactive protein (C-RP), pig major acute-phase protein (PigMAP), apolipoprotein (APO-A1) and interferon-gamma (IFN-γ). An acute phase protein index (APP Index) was calculated as follows: APP Index = (C-RP × PigMAP)/APOA1 (Heegaard et al. 2011). Data were analysed using GLM procedures (IBM SPSS, Version 21.0; USA).

Pigs fed a higher level of Trp tended to increase ADG (P = 0.080) (Table 1). Pigs fed more Trp (P = 0.036) and SAA (P = 0.028) had better FCR, and higher levels of both Trp and SAA tended to improve FCR (interaction; P = 0.092). Pigs fed more SAA had a lower APP Index (P = 0.045), while increasing Trp in the diet tended to decrease the APP Index (P = 0.075). An interaction occurred for IFN-γ, with pigs fed low Trp and high SAA having lower levels of IFN-γ, and pigs fed either low Trp and low SAA or high Trp and high SAA having higher levels of IFN-γ (P = 0.027). These data suggest that both Trp and SAA play important roles in mediating the inflammatory responses of pigs after weaning. Additional supplementation of Trp and SAA (as Met) improved performance in the 2-week period after weaning.

Table 1.  Growth performance, the acute phase protein index and plasma interferon-gamma (IFN- γ) levels in pigs fed low and high levels of tryptophan (Trp) and sulphur amino acids (SAA) and experimentally infected with E. coli after weaning