Effects of dietary tryptophan:lysine ratio and sanitary conditions on performance of weaned pigs fed antibiotic-free diets
The aim of this study was to determine the optimum standardized ileal digestible (SID) Trp:Lys ratio for weaned pigs reared in clean or unclean sanitary conditions and fed antibiotic-free diets. Mixed-sex pigs (Duroc x [Yorkshire x Landrace]; average initial BW of 7.0 ± 0.5 kg) weaned at 21 ± 1 d were randomly assigned to 10 dietary treatments in a 2 x 5 factorial arrangement in a 28-d study giving 6 replicates (3 pigs per pen) per treatment. The main factors were sanitary conditions (clean, CL and unclean, UCL) and 5 dietary SID Trp:Lys (16, 18, 20, 22 and 24%) in a completely randomized design. Diets were corn-wheat-soybean meal based with a constant SID Lys of 1.18% that was set to be seconding limiting AA. For the first 14 d, CL group (n=90) were kept in pens, followed immediately by the UCL group (n=90) for the next 14 d in the same room. Piglets were provided ad libitum access to feed and water. Under the CL condition, the room was disinfected before arrival of piglets and the room was cleaned weekly. For the UCL pigs, the room was not disinfected and cleaned after CL group and manure from swine herd was added (5 kg per pen) to the pens on d 0 and d 7 of the experiment. Pigs BW and pen feed disappearance were recorded weekly to determine ADG, ADFI and G:F. The effect of sanitary conditions was observed (P < 0.05) for ADG and G:F throughout the study. During d 0 to 7 and d 8 to 14, the ADG for CL vs. UCL were 206 vs. 160 g and 420 vs. 364 g, respectively. During d 0 to 7 and d 8 to 14, the G:F for CL vs. UCL was 0.73 vs. 0.54 and 0.76 vs. 0.64, respectively. Increasing dietary SID Trp:Lys ratio did not affect ADG and ADFI during d 0 to 14. The highest ADG was achieved at SID Trp:Lys of 20% for CL and 24% for UCL pigs, respectively. Increasing dietary Trp:Lys had a linear trend (P < 0.10) towards improved G:F during d 0 to 7 in the UCL group showing that SID Trp:Lys of 24% improved G:F. In conclusion, pigs raised under unsanitary conditions had reduced ADG and G:F in piglets, and increasing the level of SID Trp:Lys 24% could improve G:F after weaning.
Keywords: tryptophan, sanitation, piglets