Threonine and tryptophan supplementation enhance porcine respiratory and reproductive syndrome (PRRS) vaccine-induced immune responses of growing pigs.

The aim of the present study was to investigate influences of threonine and tryptophan supplementation (TTS) on immune response of growing pigs inoculated with modified live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine. Twenty growing barrows (Landrace × Yorkshire) were randomly assigned to four groups according to the PRRS vaccination and TTS. Serum samples were collected from all pigs at days 0, 7, 14, 21, 28, 35, 49 post-vaccination (day 0 defined as the day of vaccination). Pigs were euthanized and samples collected at day 49 post-vaccination. The results showed that TTS tended to increase weight gain and average daily gain (ADG) of pigs (P < 0.1). PRRS vaccine enhanced serum PRRSV-specific antibody, serum virus neutralizing (SVN) antibody and interferon-γ, interleukin (IL)-10 and IL-1β concentrations (P < 0.05). The expression of TLR3 and TLR7 mRNA in lymph nodes were higher in TTS than in the control group after PRRS vaccine inoculation (P < 0.05). TTS diet mitigated lung damage which is induced by PRRS vaccination from microscopic evaluation. These results suggest that dietary TTS could improve growth performance of growing pigs, which may be ascribed to the improved immune response and mitigated lung damage.