Effects of reduced protein and diet complexity on performance and cost of nursery pigs

Two 35-d experiments were conducted to investigate the effect of reducing crude protein by 2.5% and diet complexity with amino acid supplementation on performance and feed cost during the nursery phase. In Exp. 1 and 2, 32 PIC barrows (initial wt. = 7.28 ± 0.44 and 6.89 ± 0.77 kg, respectively) were weaned at 21 d and allotted to one of four dietary treatments in a completely randomized design (RCD) with four replicate pens per treatment with two pigs/pen. The four diets were: 1) corn-soybean meal based diet; 2) diet 1 with inclusion of fishmeal (FM) and spray-dried plasma (SDP) in Exp. 1 or soy protein concentrate (SPC) and spray-dried blood cells (SDBC) in Exp. 2; 3) low crude-protein diet (LCP) with 2.5% reduction; 4) LCP containing FM and SDP in Exp. 1 or SPC and SDBC in Exp. 2. In order to reduce CP by 2.5%, diets were supplemented with synthetic lysine, methionine, threonine and tryptophan (Trp) in Exp. 1 and in Exp. 2, LCP diets were additionally fortified with synthetic valine (Val) and isoleucine (Ile). Blood samples were collected on d 14, 21, 28 and 35 xi for determining plasma urea N (PUN). Growth performance was determined weekly. Overall in Exp. 1, pigs fed corn-soybean meal based diet containing higher CP had greater ADG (P = 0.001) than pigs fed LCP diet (0.60 vs. 0.52 kg/d, respectively) and final BW (25.28 vs. 22.95 kg, respectively) (P = 0.002). Pigs fed diets containing FM and SDP had higher final BW when compared to pigs fed less complex diets (24.87 vs. 23.35 kg, respectively) (P = 0.034). These data suggest that Val and Ile become the next limiting amino acids in LCP nursery diets. In Exp. 2, there was no effect on overall ADG and final BW. However, pigs fed HCP diets had decreased ADFI (P = 0.009) when compared to pigs fed LCP diets (0.92 vs. 1.01 kg/d, respectively). Meanwhile, pigs fed diets containing SDBC and SPC had decreased ADFI (P = 0.019) compared to pigs fed noncomplex diets (0.93 vs. 1.00 kg/d, respectively). Overall in Exp. 1 and 2, pigs fed LCP diets had lower PUN concentration (P < 0.001). Pigs fed LCP diets had an average PUN concentration of 3.47 or 3.02 mg/dl, compared to pigs fed high CP diets that had PUN concentrations of 6.69 or 6.51 mg/dl, respectively. In Exp. 1 and 2, the nursery phase resulted in LCP diets averaging $0.09 or $0.08 more per kg/gain, respectively, compared to typical corn-soybean meal animal protein based diets. In conclusion, LCP diets can be fed to nursery pigs if Val and Ile requirements are met. However, the current cost of synthetic Trp, Val and Ile do not make these diets economical.