Studies On Digestible Lys, Met+Cys, Thr, Trp Profiles Of Low Protein Content Diets For Growing Pigs

An orthogonal design of quadratic regression was used to evaluate the effect of digestible lysine (DLys), Met+Cys (DMet+Cys), Threonine (DThr), and Tryptophan(DTrp) level of corn-soybean diet on performance of growing pigs. Optimum digestible amino acids requirement and the ratio relative to DLys was obtained based on the index of performance. And two feeding experiments and two metabolic experiments were further conducted to evaluate the effect of optimum amino acids profile and to evaluate the effect of different protein level, phosphorus level and phytase supplementation diets based on this profile on performance, serum parameters and nitrogen metabolism.Exp. 1. An orthogonal design of quadratic regression was used to evaluate the effect of digestible lysine (DLys), Met+Cys (DMet+Cys), Threonine (DThr), and Tryptophan(DTrp) level (as the percentage of dietary protein) of corn-soybean diet on performance of growing pigs. Average daily gain (ADG), average feed intake (ADFI), feed convertion rate (F/G), and serum urea (BUN) were determined. Quadratic regression equation mathematical models were set up by analyzing the effect of digestible four amino acids on the ADG, F/G, ADFI, and BUN. The quadratic regression equations were as follows: For ADG(kg/d):y=-5.5680+7.5878X₁+3.0452X₂+9.1835X₃+4.2269X₄+5.2004X,X₂-1.9056X₁X₃+2.2334X₁X₄-6.005 X₁²-7.3694X₂²-7.5432X₃²-22.0732X₄² R²=0.9640 (1)For F/G:y=12.1760-9.8436X₁-19.0432X₂-2.4867X₃-11.7330X4-1.8750X₁X₂-6.8750X₁X₃+1.5625X₁X₄+8.9866X₁²+23.2745X₂²+7.9684X₃²+33.4705X₄² R²=0.9213 (2)Analysis of these two equations indicated that maximum ADG (0.775kg/d) was gained when optimum digestible amino acids levels were: DLys 0.78%, DMet+Cys 0.48%, DThr 0.51%, and DTrp 0.14%, and the ratio of these amino acids relative to DLys were: Lys:Met+Cys:Thr:Trp =100:61:64:18; Minimum F/G (2.69) was gained when optimum digestible amino acids levels were: DLys 0.77%, DMet+Cys 0.44%, DThr 0.49%, and DTrp 0.15%, and the ratio of these amino acids relative to DLys were: Lys:Met+Cys:Thr:Trp=100:57:64:20. The optimum amino acids levels and ratios were some different for gaining maximum ADG and minimum F/G, Considering obtaining maximum ADG and minimum F/G compromisingly, the optimum digestible amino acids level and ratio range of DLys, DMet+Cys, DThr and DTrp for obtaining optimum performance were: DLys 0.77⁰.78%, DMet+Cys 0.44⁰.48%, DThr 0.49⁰.51%, and DTrp 0.14⁰.15%, Lys:Met+Cys:Thr:Trp=100:57⁶1:64:18²1 respectively.Exp. 2. Ninety growing crossbred pigs(average initial BW=30±2 kg ) were used to evaluate the response to three amino acid balance diets formulated based on the result of experiment 1 with three CP levels(14%,16%,18% ) and the same content digestible Lysine, Methinine, Threonine and Tryptophan, the ratio of these digestible amino acid :100:61:64:18 was used, pigs were allocated to three treatments randomly and fed with one of three corn-soybean meal diet above. Animal performance and serum parameters were examined. It was found that protein level of the diet with the same level of digestiblelysine, sulphur amino acids, threonine and trptophan have some effect on the ADFI, ADG, and FCR, but not significantly (P<0.05). protein level had some effect on serum parameters(i>>0.05).Exp. 3. Three growing crossbred castrated male pigs(average initial BW=40±2 kg ) were used in a three-week experiment to evaluate the response to three amino acid balance diets with three CP levels( 14%, 16%, 18% ) and the same content digestible Lysine, Methinine, Threonine and Tryptophan, the ratio of these digestible amino acid:100:61:64:18 was used, A 3x3 latin-square arrangement of treatments was employed using a corn-soybean meal diet, nutrients metabolism of Nitrogen, phosphorus, energy were examined. It was found that urine and fecal N excretion were decreased and the difference of Nitrogen digestibility and retention between CP14 and 18%, CP16% and CP18% diets was significant (P<0.05). There was no significant difference between CP 14% and CP 16% in Nitrogen digestibility and retention(/>>0.05). There is significant difference among three diets in fecal N excretion, urine N excretion and total N excretion. As dietary CP decreased, fecal N excretion, urine N excretion and total N excretion decreased. However there were no significant differences for phosphorus and Energy in digestibility and retention among three diets.Exp. 4. Ninety growing pigs (DurocxLandracexYorkshire, average body weight 3O±3kg)were selected to randomly allotted to 3 treatments with 5 replicates per treatment and 6 pigs per replicates in order to evaluate the effect of different phosphorus level and phytase supplementation of low protein diet on growth performance and serum parameters. Following three corn-soybean meal diets were formulated to contain:( 1)0.30% AP-high phosphorus diet (2)0.24% AP-control diet (3)0.15% AP plus phytase supplementation. The results indicated that there is a trend to improve Average daily feed intake(ADFI), average daily gain(ADG), and feed/gain for pigs fed high phosphorus diet compared to pigs fed control diet and low phosphorus plus phytase diet. High phosphorus diet :increased average daily feed intake by 1.03%, average daily gain by 2.27% and decreased the feed to gain ratio by 1.38% compared to pigs fed control diet; increased average daily feed intake by 1.21%, average daily gain by 2.77% and decreased the feed to gain ratio by 1.75% compared to pigs fed control diet. The growth performance was comparative between control diet and low phosphorus plus phytase diet. Serum calcium concentration has a trend to decrease with the decrease of phosphorus level(P>0.05), high phosphorus diet decreased serum calcium concentration by 4.82%-. 11.08% respectively compared control diet and low phosphorus plus phytase diet. Serum phosphorus concentration has a trend to increase with the increase of phosphorus level (P<0.05), high phosphorus diet increased serum phosphorus concentration by 0.52%% 18.94% respectively compared control diet and low phosphorus plus phytase diet. The serum phosphorus concentration of control diet was higher by 18.06% than that for low phosphorus plus phytase diet(/><0.05). and no difference existed for serum phosphorus concentration between high phosphorus diet and control diet, serum ALP activity increased with the decrease of diet phosphorus level( P<0.05), serum alkaline phosphatase (ALP) activity of low phosphorus plus phytase diet was highest by 44.49%> 40.48%than that for control diets and high phosphorus diet respectively(/><0.05), and there was no difference for serum ALP activity between highphosphorus diet and control diet(P>0.05). It was concluded that increased diet phosphorus level had a trend to increase animal performance. Supplementation with 500U/ kg and in low phosphorus diet could not affect animal performance compared to that of control diet, there is a trend: to increase for serum phosphorus concentration with the increase of diet phosphorus level and to increase for serum calcium concentration to increase with the decrease of diet phosphorus level. There was a negative correlation between serum ALP and serum phosphorus concentration.Exp. 5. Three growing crossbred castrated male pigs(average initial BW=40±2 kg ) were used in a three-week metabolic experiment to evaluate the response to different phosphorus level and phytase supplementation low protein diets (0.30% high phosphorus diet, 0.24% control diet and 0.15%+phytase low phosphorus plus phytase diet) formulated based on experiment 2 and 3, with the same content digestible Lysine, Methionine, Threonine and Tryptophan, the ratio of these digestible amino acid:100:61:64:18 was used, A 3x3 latin-square arrangement of treatments was employed using a corn-soybean meal diet, N metabolism and other nutrients availability were examined. The results indicated that there is no significant difference for N metabolism between three treatments(/)>0.05). Fecal P excretion decreases with P content decrease(/><0.05), pigs fed low phosphorus plus phytase diet excreted fecal P less than 58% and 43% respectively compared with that pigs fed high phosphorus diet and control diet. However there were no significant differences for phosphorus retention among three diets(/>>0.05). Decreasing phosphorus level and supplementation of phytase had no significantly effect on the digestibility of DM, crude fat, crude fiber, crude ash, and NFE. In all, phosphorus level and supplementation of phytase has no significantly on nitrogen metabolism, and decreasing phosphorus level and supplemental phytase 500U/kg in the diet had no significantly on DM, crude fat, crude fiber, crude ash, and NFE, but increased phosphorus digestibility and significantly decreased phosph orus excretion.