Response of Rats to Diets of Equal Chemical Score: Effect of Lysine or Threonine as the Limiting Amino Acid and of an Amino Acid Excess
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Limiting
Amino acid synthesis
Essential amino acid
ABSTRACT Bread fortified with 0.48% L‐lysine (0.6% L‐lysine‐HCl) and 0.3% L‐threonine was baked at 210°C for 43 min and analyzed (lysine) calorimetrically and (threonine) microbiologically. Lysine and thre‐onine found in loaves were respectively compared with the values added to the dough. Baking loss of lysine and threonine was respectively 5 ± 6% and 3 ± 2% in the crumb and 46 ± 11% and 54 ± 8% in the crust. Loss of lysine was 14 ± 8% and of threonine 15 ± 5% in the whole loaf. However, the losses of these amino acids in the loaf could not be verified by the rat feeding test. The reason was discussed.
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Rat growth experiments and microbiological assay methods were used to estimate the loss of added free L‐lysine·HCl and DL‐threonine during the baking of wheat bread. Introductory rat experiments showed that the optimum concentration for growth of L‐lysine. HCl added before baking was approximately 0.40‐0.45% of the fresh weight of the flour. The optimum concentrations of L‐lysine·HCl and DL‐threonine when added together were approximately 0.55% for the former amino acid and 0.30% for the latter. The loss of added L‐lysine·HCl during baking was found to be 10–15% as estimated by animal experiments and 5–10% as estimated by microbiological assays. The loss of L‐threonine (added as DL‐threonine) was significantly greater, amounting to approximately 40% as judged by the feeding trials and 20–25% according to the microbiological estimations. The amino acid compositions of the flour and the bread baked from the flour were also determined.
Wheat bread
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In adult fully grown rats deficient in L-Lysine, the speed of the irreversible degradation of free L-threonine equals 1.60 mmol/24 h/g as calculated for 1 mmol/kg administered. This speed is 23 per cent slower than that determined in non lysine deficient animals. This fact explains at least partially, the paradoxical resistance of the adult rat to the lysine deficiency.
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Over a 21-d experiment, the efficiency of lysine and threonine retention was determined in 80 male Sprague-Dawley rats (65.9 ± 0.3 g, means ± SE) fed purified diets containing an amino acid mix limiting in either lysine or threonine. With additional increments of the first limiting amino acid, lysine concentration in total body protein (g/16 g N) increased (P < 0.01) in rats fed lysine-limiting diets but, when fed threonine-limiting diets, lysine concentration in body protein first increased and then decreased (P < 0.01). As increments of the first limiting amino acid were added, the threonine concentration in total body protein increased then decreased when both lysine- (P < 0.01) and threonine- (P < 0.06) limiting diets were fed. Lysine and threonine retention were calculated based on comparative slaughter. Sixteen rats were killed on d 0 to estimate the grams of amino acid in the body. Retention responses were analyzed using a logistic equation in which lysine or threonine intake was used to predict retention. The maximum marginal efficiency (dr/dl, retention/intake) was observed at <40% of maximum retention. For lysine retention, it was 81% when lysine was limiting and 70% when threonine was limiting. For threonine retention, it was 58% when threonine was limiting and 49% when lysine was limiting. The maximum cumulative efficiency (retention adjusted for maintenance relative to cumulative intake) for lysine retention was 62% when lysine was limiting or 58% when threonine was limiting. For threonine retention, it was 51% when threonine was limiting and 35% when lysine was limiting. Thus, amino acid concentration in body protein is not constant, and amino acids are used with higher efficiency when first limiting.
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To screen highly resistant varieties of wheat to lysine plus threonine, according to the principle that the varieties with high lysine content genotype has high resistance to exogenous amino acids, embryo of 40 varieties of wheat was cultured using the stress medium with different lysine and threonine(L+T) concentration, and plant growth and reaction was also observed. The results showed that the common varieties grew normal and had no inhibition or a slight suppression in the culture medium with L+T=(1+1) mmol / L; however, the most varieties were serious inhibited in the culture medium with L+T=(2+2)mmol / L. Tritium durum and varieties form Sichuan, such as E277, E93, E100, E229, Chuan 50, had high resistance to lysine plus threonine, while varieties form Henan generally had weak resistance to lysine plus threonine. Moreover, the difference between varieties that had strong resistance or weak resistance to lysine plus threonine was small, and the ratio of the former was also small.
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A total of 360 pigs (initially 22.2 lb and 31 d of age) was used in a 21-d growth assay. This trial was conducted as a combination of two separate trials in order to simultaneously examine both the true ileal digestible lysine and true ileal digestible threonine requirement and determine the appropriate threonine:lysine ratio. The first part of the trial consisted of five treatments with increasing dietary lysine (1.0. 1.1, 1.2, 1.3 and 1.4% true digestible lysine). The second part consisted of five treatments with increasing dietary threonine (0.66, 0.72, 0.78, 0.84 and 0.91% true ileal digestible threonine). The highest level of both lysine and threonine (1.4% and 0.91% respectively) served as a positive control, and this diet was combined as one treatment to give a total of nine treatments. Average daily gain increased to 1.3% true ileal digestible lysine, and then plateaued, while ADG increased to 0.78% true ileal digestible threonine, suggesting a threonine:lysine ratio of 60% for ADG. Increasing dietary lysine improved F/G linearly through 1.4% true ileal digestible lysine, while F/G improved up to a level of 0.84% true ileal digestible threonine. Using a level of 1.4% true ileal digestible lysine, a threonine:lysine ratio of approximately 60% is implicated for F/G. Amino acid and plasma urea N values were measured on d 10 of the trial. Plasma lysine concentrations were maintained steadily as the true ileal digestible lysine level increased, with a slight increase in plasma lysine concentration observed as the true ileal digestible lysine level increased from 1.3% to 1.4%. A linear increase (P<.0001) in plasma threonine concentration was observed as true ileal digestible threonine increased from 0.66% to 0.91%. Plasma urea N decreased linearly (P<0.0003) with increasing true ileal digestible lysine. As true ileal digestible threonine increased, there was no difference seen in plasma urea N concentration. Following analysis of the data, a true ileal digestible threonine to lysine ratio of 60% is suggested. A second study is in progress where the higher true digestible lysine level of 1.5% is used to verify trial results.; Swine Day, 2003, Kansas State University, Manhattan, KS, 2003
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Two experiments were conducted to determine the efficiency of dietary lysine and threonine retention for carcass protein accretion in pigs within a body weight range of 10–20 kg. At the beginning of the experiments, an initial representative group of 6 pigs were killed for carcass compositional analysis. In the first experiment, conducted to determine the efficiency of dietary lysine retention, a basal diet was formulated to contain 6 g of lysine kg −1 . Twelve pigs were fed the basal diet supplemented with L-lysine∙HCl to contain 6, 7, or 8 g of lysine kg −1 . Daily weight gain and gain:feed ratio were higher (P < 0.05) for pigs fed 8 g of lysine than for pigs fed 6 g of lysine kg −1 diet. The accretion rates of dry matter, protein, ash, and lysine in the carcass were higher for pigs fed 8 g of lysine than for pigs fed 6 g of lysine kg −1 diet. A linear regression of daily carcass lysine accretion on daily lysine intake resulted in a 72% efficiency of carcass lysine accretion above maintenance. In the second experiment, three diets including a basal diet formulated to contain 4 g of threonine kg −1 and supplemented with L-threonine to contain 4, 4.65, or 5.3 g of threonine kg −1 were fed to 12 pigs. Rate and efficiency of body weight gain exhibited a dose-response improvement (P < 0.05) to an increase in dietary threonine. Carcass protein, ash, and threonine accretion rates were higher (P < 0.05) for pigs fed 5.3 g of threonine than those fed 4 g of threonine kg −1 diet. Linear regression of daily carcass threonine accretion on daily threonine intake resulted in extra-maintenance efficiency of threonine retention of 60%. The efficiencies of dietary lysine and threonine utilization for carcass growth in pigs within the liveweight range of 10–20 kg are 72 and 60%, respectively. Key words: Lysine, threonine, retention efficiency, amino acids, pigs
Basal (medicine)
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A total of 1800 pigs (Exp 1, 360; Exp. 2, 1440) were used in two experiments to evaluate the true ileal digestible (TID) lysine and threonine requirement for 24- to 44-lb pigs. In Exp. 1, there were eight pens per treatment, with five pigs (Genetiporc, initially 23.6 lb and 34 d of age) per pen. Experiment 1 was conducted as a combination of two separate trials to simultaneously examine both the TID lysine and threonine requirement, and hence, determine the appropriate threonine-to-lysine ratio. The first part of the trial consisted of five treatments formulated to contain 0.9, 1.0, 1.1, 1.2, or 1.3% TID lysine, with TID threonine at 66% of lysine. The second part consisted of five treatments formulated to 1.3% TID lysine with increasing TID threonine (0.60, 0.66, 0.73, 0.79, or 0.85%). Other amino acids were formulated to either meet or exceed requirement estimates, thereby ensuring lysine and threonine were first limiting. The highest concentrations of both lysine and threonine (1.3% and 0.85%, respectively) were combined in a single diet, which was used in both trials, to give a total of 10 treatments. From d 0 to 17, ADG and feed efficiency (F/G) improved as TID lysine (quadratic, P<0.02) and threonine (ADG, linear, P<0.03; F/G, quadratic, P<0.04) increased. Regression analysis showed that 95% or more of the maximum response was obtained at a TID threonine-to-lysine ratio of approximately 64% for ADG and 66% for F/G. In Exp. 2, there were 48 pigs per experimental unit (2 pens sharing a fenceline feeder) and six replications per treatment. Pigs (PIC, 24 lb and 39 d of age) were fed experimental diets containing 1.1% TID lysine (calculated to be less than their requirement estimate), with added Lthreonine to give TID threonine concentrations of 0.55, 0.60, 0.66, 0.72, or 0.77% and TID threonine-to-lysine ratios of 50, 55, 60, 65, and 70%. For the 21-d trial, ADG (quadratic, P<0.07) and F/G (quadratic, P<0.01) improved with increasing TID threonine. The best ADG and F/G were observed at 0.72% TID threonine. Hence, it seems that pigs weighing between 22 and 44 lb require approximately 0.72% TID threonine (0.81% total threonine) when fed 1.1% TID lysine, which corresponds to a TID threonine-tolysine ratio of 65%, similar to results in Exp. 1. Data from these two studies indicate an optimal TID threonine-to-lysine ratio of approximately 64 to 66% for 24- to 44-lb pigs.; Swine Day, 2004, Kansas State University, Manhattan, KS, 2004
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Determining the optimal threonine: lysine ratio in starter diets for the segregated early-weaned pig
A 35-day growth trial was conducted to determine the threonine: lysine ratio necessary to optimize growth performance of the segregated early-weaned (SEW) pig. Twelve experimental diets included two levels of lysine (1.15% and 1.5% digestible lysine) and six digestible threonine:lysine ratios (50, 55, 60, 65, 70, and 75%) in a 2 x 6 factorial arrangement. Growth performance was improved by feeding 1.5% digestible lysine, rather than 1. 15% digestible lysine. However, growth performance was not improved by increasing dietary threonine. These data indicate that the threonine requirement is no more than 50% of digestible lysine.; Swine Day, Manhattan, KS, November 16, 1995
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