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Effects of dietary threonine:lysine ratio and sanitary conditions on performance and plasma urea nitrogen of weaned pigs fed antibiotic-free diets
A growth trial was conducted to determine the optimum standardized ileal digestible (SID) Thr:Lys ratio for weaned piglets 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 42-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 Thr:Lys ratios (55, 59, 63, 67 and 71%) 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. Pigs had ad libitum access to feed and water. For the first 21 d, CL group (90 piglets) were kept in a room that was disinfected before arrival of piglets and was cleaned weekly. The UCL group (90 piglets) followed immediately for the next 21 d in the same room. The UCL room was not disinfected and left uncleaned 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 and pen feed disappearance were recorded weekly to determine ADG, ADFI and G:F. Blood samples were collected on d 0 and d 14 via jugular venipuncture for determination of plasma urea nitrogen (PUN). There were no significant interactions (P > 0.05) between sanitary conditions and dietary levels on any response criteria. Unclean conditions reduced (P < 0.05) ADG and ADFI throughout the experimental period, and tended to reduce (P < 0.10) G:F. The overall ADG was 494 vs. 404 g and ADFI was 736 vs. 579 g, for CL and UCL, respectively. Unclean group had significantly higher (P<0.05) PUN (4.12 vs. 2.96) on d 14 compared to CL group. Increasing dietary SID Thr:Lys ratio had no effect on ADG and ADFI throughout the study, however, there was a linear trend (P <0.10) in G:F showing that SID Thr:Lys of 71% improved G:F. The highest ADG was achieved at SID Thr:Lys of 71% for CL and 67% for UCL pigs, respectively. In conclusion, unclean conditions reduced ADG and ADFI in piglets, and increasing levels of SID Thr:Lys to 71% could improve G:F after weaning.
Keywords: threonine, sanitation, piglets