Study On The Limiting Amino Acid Pattern For Late Finishing Pigs Fed Protein Reduced Diet

Five experiments including468late finishing gilts (Duroc x Landrace x Large White) were conducted to estimate the optimum ratio to standardized ileal digestible (SID) lysine (Lys) of threonine (Thr), sulfur amino acid (SAA) and trytophan (Trp) for finishing gilts fed low protein diets. In Exp.1,108gilts (87.8±5.9kg) were randomly allotted to1of6diets which consisted of a high CP (13.5%) diet with0.61%SID Lys or5low CP (10%) diets providing SID Lys levels of0.49%,0.55%,0.61%,0.67%and0.73%, respectively. Gilts were housed in3pigs per pen with6pens per treatment. At the end of the28day experiment,36gilts (one pig per pen) with average body weight (BW) of116kg were killed to evaluate carcass traits. Increasing SID Lys increased ADG (linear and quadratic effect, P<0.05) and also improved FCR (linear and quadratic effect, P<0.05). SUN decreased as the SID Lys increased (linear and quadratic effect, P<0.05). The SID Lys levels required to maximize average daily gain (ADG) and optimize feed conversion ratio (FCR) as well as to minimize serum urea nitrogen (SUN) levels were0.57%,0.58%and0.61%using a linear-break point model and0.65%,0.65%and0.66%using a quadratic model. The fat-free lean gain tended to increase linearly with the increase in dietary SID Lys levels from0.49%to0.73%when gilts receiving a low CP diet (linear effect, P=0.06). Exp.2-4were the dose response studies and formulated to contain0.51%SID Lys (which is slightly lower than the gilt’s requirement) with SID Thr to Lys ratios of0.54,0.60,0.66,0.72and0.78(Exp.2, intial BW90.6±5.7kg), SID Trp to Lys ratios of0.12,0.15,0.18,0.21and0.24(Exp.3, intial BW89.1±5.1kg), and SID SAA to Lys ratios of0.48,0.53,0.58,0.63and0.68(Exp.4, intial BW96.6±5.6kg), respectively, In Exp.2, increased ratios of dietary SID Thr to Lys from0.54to0.78resulted in an increase in ADG (linear and quadratic effect, P<0.05) and an improvement in FCR (linear and quadratic effect, P<0.05). SUN (linear and quadratic effect, P<0.05) decreased as dietary SID Thr to Lys ratio increased. With the exception of L*lightness (linear effect, P<0.05), no effects on carcass characteristics were observed with the increase in dietary SID Thr to Lys ratio. Linear-break point analysis estimated the break points of dietary SID Thr to Lys ratio as0.61,0.63and0.64to maximize ADG, optimize FCR and minimize SUN, respectively. Quadratic analysis estimated the optimum SID Thr to Lys ratios as0.70,0.75and0.74to maximize ADG, optimize FCR and minimize SUN, respectively. In Exp.3, ADG increased (linear and quadratic effect, P<0.05), FCR improved (linear and quadratic effect, P<0.05) as the SID Trp to Lys ratio increased. Increased SID Trp to Lys ratio resulted in a decrease in SUN (linear and quadratic effect, P<0.05). L*lightness (quadratic effect, P<0.05) and marbling (quadratic effect, P<0.05) were affected by increasing the SID Trp to Lys ratio from0.12to0.24. The linear broken-line model estimated the optimum dietary SID Trp to Lys ratios as0.16,0.17and0.16to maximize ADG and FCR and minimize SUN. The quadratic analysis model estimated the optimum SID Trp to Lys ratios as0.20,0.20and0.20to maximize ADG and FCR and minimize SUN. In Exp.4, increasing the SID SAA to Lys ratio increased ADG (linear and quadratic effect, P<0.05), improved FCR (linear and quadratic effect, P<0.05) and decreased SUN concentration (linear and quadratic effect, P<0.05) of finishing gilts. No effect was obtained for carcass traits. The optimum SID SAA to Lys ratios to maximize ADG as well as to minimize FCR and SUN levels were0.57,0.58and0.53using a linear-break point model and0.64,0.62and0.61using a quadratic model. In Exp.5,90gilts (93.8±5.5kg) were randomly allotted to1of5diets which consisted of a high CP (13.6%CP) diet with0.64%SID Lys or4low CP (10.5%CP) diets with0.70%SID Lys. The basal diet was formulated by supplementing Lys, Thr and SAA in a low CP diet. The diets of Ⅱ, Ⅲ, and Ⅳ were supplemented with Trp, Trp+Val or Trp+Val+Ile orderly on the basis of basal diet. The highest ADG was obtained in gilts fed the diet III, which was higher than gilts fed the basal diet (P<0.05). The highest level of SUN was obtained in gilts fed the normal CP diet, which was higher than other treatments (P<0.05). The fat-free lean gain (quadratic effect, P<0.05) and ADG increased (linear and quadratic effect, P<0.05), SUN decreased (linear and quadratic effect, P<0.05) as adding the crystalline amino acids gradually in the low CP diets.