Estimating the standardised ileal digestible tryptophan requirement of pigs kept under commercial conditions in the immediate post-weaning period

Animal Feed Science and Technology, January 2020. Vol 259: 114342

J. C. Kim, J. K. Htoo C. F. M. de Lange, B. P. Mullan, J. W. Resink, C. F. Hansen, P. A. Stumbles, D. J. Hampson, N. Ferguson and J. R. Pluske

by M. M. Capozzalo on 09/12/2019
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Animal Feed Science and Technology


This experiment was conducted to determine the optimum standardised ileal digestible (SID) ratio of tryptophan (Trp) to lysine (Lys; Trp:Lys) for commercially housed pigs fed without a dietary antibiotic, but including pharmacological levels of zinc oxide in the immediate post-weaning period. The hypothesis tested was that pigs would positively respond to an increased SID Trp:Lys ratio with improved performance indices and lower levels of circulating biomarkers indicative of an inflammatory response. Forty-two pens were randomly allocated to 1 of 6 treatment groups with varied levels of calculated dietary SID Trp:Lys ratios (0.16, 0.18, 0.20, 0.22, 0.24 and 0.26). Male to female ratios were 3:4 in treatments with 0.16, 0.20, 0.24 SID Trp:Lys and 4:3 for treatments with 0.18, 0.22 and 0.26 SID Trp:Lys. A total of 2430 pigs (6.3 ± 1.09 kg; weaning occurred between 17–20 days (d) of age) were then allocated to 42 pens according to sex and a visual estimate of weight (medium and heavy). Pigs were weighed as a pen on d 1, 8 and 15. Diets were fed for 2 weeks after weaning. Blood samples were taken on d 5 and d 12, with C-reactive protein (C-RP) levels determined on d 5 and d 12 and haptoglobin and plasma urea (PU) levels determined on d 12. Based on analysed amino acid contents in the diets, calculations were made based on SID coefficients and the SID Trp:Lys ratios in diets 1–6 were corrected to 0.168, 0.182, 0.205, 0.211, 0.234 and 0.253. The greatest average daily gain (ADG) and optimal feed conversion ratio (FCR) during the overall 2-week period after weaning were achieved with pigs fed a diet with 0.234 SID Trp:Lys (P =0.05). Levels of C-RP showed a strong trend whereby pigs fed a SID Trp:Lys ratio of 0.253 had the lowest C-RP values and pigs fed a SID Trp:Lys ratio of 0.234 had the highest C-RP values (P =0.061). No differences were found for plasma levels of PU or haptoglobin (P > 0.05) between ratios, suggesting that pigs in the present trial were not under a significant inflammation challenge. Nevertheless, a dietary ratio of 0.234 SID Trp:Lys was found to optimise both ADG and FCR of weaned pigs.