Dietary crude protein has minimal effect on the activity of selected enzymes of methionine catabolism in kittens fed diets near-limiting in methionine

Previous experiments have shown that increasing the dietary crude protein (CP) of cats does not increase urea cycle enzymes or alanine amino transferase as occurs in rats. Also when an essential amino acid (EAA) is limiting in a diet for growing kittens, the kittens do not exhibit an amino acid imbalance when other EAAs are added to the diet. To study the metabolic basis for these observations which are different from that found in omnivores and herbivores, the hypothesis that increased dietary CP decreases methionine catabolism, so more is spared for growth, was tested. Fifteen male kittens were randomly assigned to one of three dietary treatments. Each diet contained 2.5 g l-methionine/kg diet and 200, 300 or 500 g CP/kg diet. The livers and kidneys were removed and assayed for methionine transaminase (MTA), cystathionase (CASE) and cystathionine synthase (CS). Free amino acid concentrations were determined in liver, kidney and plasma. The 300 and 500 g CP/kg groups had significantly greater kidney weights and body weight gains than the 200 g CP/kg group. Hepatic MTA activity was lower in the 300 than the 200 or 500 g CP/kg groups (p < 0.05). Renal MTA and CASE activities were 35% and 50% greater, respectively, for the 500 g CP/kg group than for the 200 g CP/kg diet group (p < 0.05). Renal CS activities for the 300 and 500 g CP/kg groups were 29% (p > 0.05) and 38% (p < 0.05) greater, respectively, than the 200 g CP/kg group. Cyst(e)ine concentrations were lower in the livers of the 500 g CP/kg group than the 200 g CP/kg group (p < 0.05). Cystathionine was lower in plasma and kidney from the 500 g CP/kg diet group than from the 200 g CP/kg diet group (p < 0.05). It was concluded that the metabolic basis for the increased growth of kittens fed diets marginally limiting in methionine, with increasing concentrations of dietary CP, was not mediated through decreased enzyme activity associated with the catabolism of methionine, but was the result of an increase in food (methionine) intake.     

Increasing dietary crude protein does not increase the methionine requirement in kittens

The objective of this study was to determine if the methionine (met) requirement of kittens is correlated with the concentration of dietary crude protein (CP). The study used 48 male kittens in two replications of six 4 x 4 Latin squares, each representing one concentration of met (1.5, 2.5, 3.5, 4.5, 6.0 or 9.0 g/kg diet) with four CP concentrations (150, 200, 300 and 500 g/kg diet) in 2-week periods. Cystine was present in the lowest CP diet at 5.3 g/kg diet and increased as dietary CP increased. Body weight gain, food intake, nitrogen balance and plasma amino acids, glucose, insulin, cortisol, somatomedin C, T(3) and T(4) concentrations on day 12 were measured. From breakpoint analysis of the nitrogen retention curves, the met requirement of kittens was found to be 3.1, 3.8, 3.1 and 2.4 g met/kg for the 150, 200, 300 and 500 g CP/kg diets, respectively. When met was limiting (1.5 or 2.5 g/kg diet), increasing dietary CP did not decrease, but rather increased food intake, body weight gain and nitrogen retention. Plasma met concentrations increased as dietary met increased and at 2.5-3.5 g met/kg diet were not different among kittens fed the various CP diets. Total plasma T(3) and T(4) increased significantly as dietary CP increased in kittens given the 2.5 and 4.5 g met/kg diets. Results indicate that food intake and possibly altered hormonal secretion play a role in this growth response. In conclusion, the met requirement of growing kittens, unlike omnivores and herbivores studied, was not positively correlated with the concentration of dietary CP.     

Advances in low-protein diets for swine

Recent years have witnessed the great advantages of reducing dietary crude protein(CP) with free amino acids(AA)supplementation for sustainable swine industry, including saving protein ingredients, reducing nitrogen excretion, feed costs and the risk of gut disorders without impairing growth performance compared to traditional diets. However, a tendency toward increased fatness is a matter of concern when pigs are fed low-protein(LP) diets. In response, the use of the net energy system and balanced AA for formulation of LP diets has been proposed as a solution. Moreover, the extent to which dietary CP can be reduced is complicated. Meanwhile, the requirements for the first five limiting AA(lysine, threonine, sulfur-containing AA, tryptophan, and valine) that growing-finishing pigs fed LP diets were higher than pigs fed traditional diets, because the need for nitrogen for endogenous synthesis of non-essential AA to support protein synthesis may be increased when dietary CP is lowered. Overall, to address these concerns and give a better understanding of this nutritional strategy, this paper reviews recent advances in the study of LP diets for swine and provides some insights into future research directions.     

Nitrogen balance and ileal amino acid digestibility in growing pigs fed diets reduced in protein concentration

Two studies were conducted to assess the effect of dietary protein reduction on N utilization, N excretion, and AA digestibility in growing pigs. The objective was to determine whether pigs fed diets with a reduced CP concentration could maintain the same N retention as pigs fed an adequate diet. The second objective was to test whether reducing dietary CP concentration decreases AA digestibility. In each study, six barrows were allotted to one of six dietary treatments in a Latin square design. Treatments consisted of four corn-soybean meal-based diets containing 15, 12, 9, and 6% CP, a casein-based diet containing 15% CP, and a protein-free diet. Crystalline AA were included in the 12, 9, and 6% CP diets. The indispensable:dispensable AA ratio was maintained at 45:55 with the addition of L-glutamic acid to the 9 and 6% CP diets. The casein-based and protein-free diets were used to determine endogenous total tract N and ileal AA losses. In the first study, total N losses and N absorbed decreased linearly (P < 0.001) as dietary CP concentration decreased from 15 to 6%. Both a linear (P < 0.001) and a quadratic (P < 0.05) decrease in N retention were found with decreasing dietary CP concentration. Nitrogen retained as a percentage of intake and absorbed increased (P < 0.001) as dietary CP concentration was reduced from 15 to 6%. In the second study, six barrows were surgically fitted with a T-cannula at the terminal ileum to determine ileal AA digestibility. For all dispensable and most indispensable AA, apparent and standardized ileal digestibility increased linearly (P 0.01, and for arginine, P < 0.05) as dietary CP concentration decreased. These results indicate that dietary CP concentration can be decreased from 15 to 12% with crystalline AA supplementation to meet an ideal AA profile without adversely affecting N retention, and that decreasing dietary CP concentration from 15 to 6% increases both dispensable and indispensable AA ileal digestibility.     

Limiting order of amino acids and the effects of phytase on protein quality in corn gluten meal fed to young chicks

An amino acid deletion assay, a protein efficiency ratio (PER) assay, and a slope-ratio growth assay were used to establish the limiting order of AA, and to determine the effects of microbial phytase on protein utilization in corn gluten meal (CGM) fed to chicks during the period of 8 to 21 d posthatching. In Assay 1, a 12% CP CGM diet was fortified with AA to fulfill the digestible AA ideal profile (only Phe + Tyr, Leu, and Pro exceeded requirements) for young chicks. Amino acids were then individually deleted, and all diets were fortified to 23% CP, with Glu varying as necessary. A Met-fortified 23% CP corn-soybean meal diet served as a positive control. No weight gain or feed efficiency differences were observed between the fully fortified CGM basal diet and the corn-soybean meal positive-control diet. The limiting order of AA established in CGM was 1) Lys, 2) Trp, 3) Arg, 4) Thr, 5) Val, 6) Ile, 7) His, 8) cystine, and 9) Met. In Assay 2, diets with 10% CP furnished by CGM or casein were fed in the presence and absence of 1,200 U/kg phytase. A protein source x phytase interaction (P < 0.05) was observed for weight gain, gain:feed, and PER, indicating positive responses to phytase when casein was fed but negative responses to phytase when CGM was fed. In Assay 3, graded levels of protein (8, 16, and 24% CP) furnished by CGM were fed in the presence and absence of 1,200 U/kg phytase. Weight gain and gain:feed increased linearly (P < 0.05) as a function of protein intake, but phytase supplementation had no effect on weight gain or gain:feed slopes. These results indicate that 1,200 U/kg phytase did not increase either CP or AA utilization in CGM for young chicks.     

Effects of citric acid and microbial phytase on amino acid digestibility in broiler chickens

1. Two experiments with growing chickens were carried out to study the effects of the inclusion of a microbial phytase (Natuphos 5000) and citric acid (CA) in maize-soybean-based diets on the performance and apparent ileal digestibility (AID) of crude protein (CP) and amino acids (AA). In both experiments the diets were formulated to contain the same amounts of energy and protein. 2. In the first experiment, data were analysed as a 2 x 2 factorial arrangement with two concentrations of available phosphorus (AP) from one day to 3 weeks of age (3.5 and 2.2 g/kg) and for 3 to 6 weeks (2.7 and 1.4 g/kg), and two inclusions of commercial phytase (0 and 500 FTU/kg) in each period. The AID of CP and dispensable and indispensable AA were not modified by the AP content of the diet. Addition of phytase improved the AID of CP and dispensable and indispensable AA only at low AP levels. 3. In the second experiment, data were analysed as a 3 x 2 factorial arrangement with three concentrations of citric acid (0, 20 and 50 g/kg) and two inclusions of commercial phytase (0 and 750 FTU/kg). Diets were formulated with deficient contents of AP (2.5 g/kg). Performance was not affected by commercial phytase addition. The addition of CA reduced the weight gain but did not modify the feed intake and gain:feed. In general, the AID of CP and dispensable and indispensable AA were not affected by CA addition. Commercial phytase increased the apparent ileal digestibility of crude protein but had no effect on AID of dispensable and indispensable AA. 4. In conclusion, the present work showed that microbial phytase enhanced AA digestibility in maize-soy-based diet only at very low AP concentrations, and that CA had no affect on the AID of CP and dispensable and indispensable AA. No synergism between CA and microbial phytase was detected.     

Nitrogen metabolism and growth performance of gilts fed standard corn-soybean meal diets or low-crude protein,amino acid-supplemented diets

Two experiments were conducted to determine the CP concentration below which N retention and growth performance are reduced when low-protein, amino acid-supplemented, corn-soybean meal diets are fed. In a N balance trial (Exp. 1), 12 gilts (initial weight 41 kg) were fitted with urinary catheters and fed six different diets during three 7-d periods in an incomplete block design. The diets were: 1) 18% CP; 2) 14% CP + AA, 3) 16% CP; 4) 12% CP + AA; 5) 14% CP; and 6) 10% CP + AA. Amino acids (lysine, threonine, tryptophan, and methionine) were supplemented such that the concentrations in the low-protein diets were equal to those in their standard (4% CP higher) counterparts. Nitrogen retention (g/d) decreased (P < 0.01) as CP decreased, in both standard (27.10, 24.53, and 20.99) and low-protein (21.51, 19.18, and 15.83) diets, but was lower (P < 0.01) in low-protein diets. There were no differences among treatments (P > 0.05) in biological value (68.2% standard vs 71.0% low-protein). In a growth performance trial (Exp. 2), 36 gilts (initial weight 19.5 kg) were penned individually and fed one of six diets for 35 d in a randomized complete block design. Dietary treatments were a 16% CP standard diet and low-protein diets formulated to contain 15, 14, 13, 12, and 11% CP supplemented with crystalline lysine, tryptophan, threonine, and methionine to equal the total concentrations in the standard diet. Protein concentration affected (P < or = 0.05) ADG, ADFI, feed efficiency, fat-free lean gain, longissimus muscle area, plasma urea, and plasma concentrations of most essential AA. For most of these traits, the major difference was poor performance of pigs fed the 11% CP diet. Thus, in Exp. 1, at AA concentrations from deficient to excess, low-protein, amino acid-supplemented diets failed to produce the same N retention as the equivalent corn-soybean meal diets. However in Exp. 2, the same performance was obtained with 16, 15, 14, 13, and 12% CP. Based on these data, we suggest that N balance is more sensitive than growth to amino acid adequacy andthat other AA (e.g., isoleucine and valine) may limit growth performance when the protein concentration is reduced by more than four percentage units.     

Dietary protein levels and amino acid supplementation patterns alter the composition and functions of colonic microbiota in pigs

Different dietary nitrogen (N) patterns may have different effects on gut microbiota. To investigate the effects of different crude protein (CP) levels or essential amino acids (EAA) supplementation patterns on the structure and functions of colonic microbiota, 42 barrows (25 ± 0.39 kg) were randomly assigned to 7 dietary treatments including: diet 1, a high CP diet with balanced 10 EAA; diet 2, a medium CP diet with approximately 2% decreased CP level from diet 1 and balanced 10 EAA; diets 3, 4, 5, 6 and 7, low CP diets with 4% decreased CP level from diet 1. Specifically, diet 3 was only balanced for Lys, Met, Thr and Trp; diets 4, 5 and 6 were further supplemented with Ile, Val and Ile + Val on the basis of diet 3, respectively; and diet 7 was balanced for 10 EAA. Results over a 110-d trial showed that reducing the CP level by 2% or 4% dramatically decreased N intake and excretion (P < 0.05) in the presence of balanced 10 EAA, which was not observed when altering the EAA supplementation patterns in low CP diet (−4%). With balanced 10 EAA, 2% reduction in dietary CP significantly reduced Firmicutes-to-Bacteroidetes (F:B) ratio and significantly elevated the abundance of Prevotellaceae NK3B31 (P < 0.05); whereas 4% reduction evidently increased the abundances of Proteobacteria, Succinivibrio and Lachnospiraceae XPB1014 (P < 0.05). Among the 5 low CP diets (−4%), supplementation with Ile, or Val + Ile, or balanced 10 EAA increased F:B ratio and the abundance of Proteobacteria. In addition, the predicted functions revealed that different CP levels and EAA balanced patterns dramatically altered the mRNA expression profiles of N-metabolizing genes, the “N and energy metabolism” pathways or the metabolism of some small substances, such as amino acids (AA) and vitamins. Our findings suggested that reducing the dietary CP levels by 2% to 4% with balancing 10 EAA, or only further supplementation with Ile or Val + Ile to a low protein diet (−4%) reduced the N contents entering the hindgut to various degrees, altered the abundances of N-metabolizing bacteria, and improved the abilities of N utilization.     

Influence of dietary protein and carbohydrate sources on nitrogen metabolism and carbohydrate fermentation by ruminal microbes in continuous culture

Four diets containing 15% CP were formulated to study the effects of dietary carbohydrate and protein sources on N metabolism and carbohydrate fermentation by ruminal bacteria. Diets were supplied to eight dual-flow continuous culture fermenters during three experimental periods in a randomized complete block design. Six replications were obtained for each diet. Treatments were arranged as a 2 X 2 factorial with two carbohydrate and two protein sources. Carbohydrate sources were corn and barley and protein sources were soybean meal (SBM) and fish meal (FM). Approximately 40% of the dietary CP was derived from SBM or FM and corn or barley provided 39% of dietary DM. All diets contained 15% grass hay, 20% wheat straw, and 10.1 to 15.3% solka floc (DM basis). Interactions (P less than .05) were observed between dietary carbohydrate and protein sources, resulting in a depression of VFA production (moles/day) and digestion (percentage) of ADF and cellulose when the corn-FM diet was fed. True OM digestion (percentage) was higher (P less than .05) for SBM than for FM diets and for corn than for barley diets. Although dietary CP degradation (percentage) was higher (P less than .05) for SBM than for FM diets, non-NH3 N in the effluent (grams/day) was not different among diets due to a greater (P less than .05) bacterial N flow for SBM than for FM diets. Despite the lower amino acid (AA) intake (P less than .05) for corn than for barley diets and also for FM than for SBM diets, flows (grams/day) of total AA, essential AA (EAA), and nonessential AA (NEAA) were similar (P greater than .05) among diets. However, greater (P less than .05) total AA, EAA, and NEAA flows (percentage of AA intake) were found for corn than for barley diets and for FM than for SBM diets. It is concluded, therefore, that ruminal escape protein derived from corn or FM has a significant effect on manipulating AA leaving the ruminal fermentation.     

Effects of high peanut meal with different crude protein level supplemented with amino acids on performance,carcass traits and nitrogen retention of Chinese Yellow broilers

This study assessed the effects of feeding high peanut meal diets of reduced crude protein (CP) content supplemented with essential amino acids (EAA) on growth performance, carcass traits, biochemical indices in plasma, and nitrogen (N) retention of male and female Lingnan Yellow broilers from day 22 to day 42 of age. Each of four dietary treatments (19%, 18%, 17% or 16% CP, dietary CP level reduced by the reduced dietary peanut meal) contained six replicate pens with 35 birds of each sex (males and females with equal number), separately (1680 in total). The three diets with reduced CP were supplemented with 5 EAA to meet the requirements and provide the same levels as in the 19% CP diet. Average daily gain decreased and feed:gain ratio was worse in both sexes with reduced CP% (linear, p < 0.05). Dressing percentage increased as CP% decreased in males (linear, p < 0.05) and thigh muscle percentage reduced slightly in females (linear, p < 0.05). Abdominal fat percentage of males fed the 17% CP was the lowest (quadratic, p < 0.05). The plasma metabolic indices, concentrations of triglycerides and malondialdehyde, showed linear responses to reduced CP% (p < 0.05) with triglycerides increasing while malondialdehyde decreased. Plasma uric acid increased in females (linear, p < 0.05), but not in males, as CP% decreased. Efficiency of N retention increased and N excretion strikingly decreased with lower CP diets (p < 0.001), and both variables showed significant (p < 0.05) linear and quadratic effects. It is concluded that there was a limit to which dietary CP of broilers could be reduced without adverse effects. Dietary CP could be reduced to 17% for males and 18% for females (or 18% when fed together) between day 22 and day 42, if diets are supplemented with synthetic EAA.     

Effect of dietary crude protein level on basal ileal endogenous losses and standardized ileal digestibilities of crude protein and amino acids in newly weaned pigs

The study was carried out to estimate basal ileal endogenous crude protein and amino acid losses (IAAL_B) and standardized ileal digestibilities (SID) of crude protein (CP) and amino acids (AA) originating from casein in newly weaned pigs from linear relationships between ileal recoveries and dietary intakes of graded levels of CP and AA. A total of 14 (12 + 2 for replacement) 3‐week‐old barrows weighing 5.7 kg was fitted with simple T cannulas at the distal ileum. At 28 days of age, the pigs were randomly allocated to the six experimental diets with two pigs per diet in four weekly repeated measurements. Corn starch‐based diets, containing six graded levels of CP from casein (90, 155, 220, 285, 350, 415 g/kg CP as‐fed basis respectively), were formulated. Titanium dioxide (TiO₂) was included as a digestibility marker. Each experimental period consisted of 7 days. Ileal digesta were collected for a total of 24 h during day 6 and 8. Splitting the total range of 90 to 415 g/kg CP into smaller ranges, i.e. from 90 to 220, 220 to 350 or 285 to 415 g/kg CP, provides estimates for CP and AA recoveries which are not significantly different from zero. As a result, dietary CP and AA originating from casein are completely digested and absorbed until the end of the small intestine. In addition, the use of large ranges of dietary CP levels showed that IAAL_B were affected (p < 0.050) by the dietary CP content. Accepting that ileal recoveries of CP and AA are exclusively of endogenous origin when purified corn starch casein‐based diets are fed, IAAL_B were estimated as a function of the dietary CP level. There were linear increases (p < 0.050) in IAAL_B when the dietary CP content was increased from 90 to 415 g/kg. Average IAAL_B expressed in g/kg dry matter intake (DMI) were 16.3, 0.7, 0.2, 0.9 and 0.2 for CP, lysine, methionine, threonine and tryptophan respectively. These values are in close agreement with IAAL_B obtained in grower‐finisher pigs.     

Ideal amino acid pattern for 10-kilogram pigs.

Two growth assays and one nitrogen balance experiment were conducted to develop an ideal amino acid pattern for 10-kg pigs. Crossbred pigs were fed chemically defined amino acid diets containing four indispensable amino acid (AA) patterns: 1) the Illinois final amino acid pattern (IFP), a recently developed AA profile for purified diets; 2) the Illinois ideal amino acid pattern (IIP), a modification of IFP; 3) the Wang and Fuller ideal amino acid pattern (WFIP); and 4) the 1988 National Research Council (NRC) amino acid requirement pattern for 10-kg pigs (NRCP). A mixture of dispensable AA consisting of glutamate, glycine, and proline that had been proven to be an efficient mixture of dispensable AA nitrogen was fed together with the indispensable AA patterns. Diets were made isonitrogenous and isoenergetic within experiments. In Exp. 1, pigs were given ad libitum access to experimental diets with AA levels set above the NRC AA requirements. Regardless of which AA pattern was fed, pigs had similar (P greater than .05) daily gains, daily feed intakes, and gain:feed ratios. In Exp. 2, all levels of indispensable and dispensable AA were reduced to 50% of levels present in Exp. 1. When pigs had ad libitum access to these diets, daily gains of pigs fed IIP were superior (P greater than .05) to those of pigs fed IFP or NRCP, but similar (P greater than .05) weight gains occurred in pigs fed IFP, WFIP, and NRCP. In Exp. 3, the efficiency of nitrogen utilization of the four indispensable AA patterns was evaluated by a nitrogen balance experiment in pigs equally fed the same experimental diets fed in Exp. 2. Pigs fed NRCP utilized nitrogen with an efficiency of 74%, which was less (P less than .001) than the efficiencies of 79 to 80% obtained in pigs fed IFP, IIP, and WFIP. Nitrogen retained (grams) per gram of nitrogen intake from indispensable AA was greater (P less than .01) for IIP than for either IFP or WFIP. The results of these experiments indicate that WFIP contains excesses of leucine, valine, phenylalanine plus tyrosine, methionine plus cystine, and threonine for pigs between 10 and 20 kg BW. Also, NRCP is probably first-limiting in leucine and also limiting in other AA, resulting in lower nitrogen utilization than IIP. The pattern of indispensable AA in IIP (grams of AA/100 g lysine) is as follows: lysine (100), methionine+cystine (60), threonine (65), tryptophan (18), phenylalanine+tyrosine (95), leucine (100), isoleucine (60), valine (68), arginine (42), and histidine (32).     

Energy utilization of low-protein diets in growing pigs

Three trials were conducted to measure the effects of reducing the dietary CP content on digestive and metabolic utilization of N and energy in growing pigs. Sixty barrows weighing about 65 kg were used. In Trial 1, four semisynthetic diets with CP content decreasing from 18.9 to 12.3% were formulated. In Trials 2 and 3, two diets with 17.4 and 13.9% CP were formulated using conventional ingredients. In the three trials, diets were supplemented with variable amounts of industrial AA in order to maintain a constant standardized digestible lysine/NE ratio (0.76 g/MJ) and ratios between essential AA relative to lysine of at least 60, 65, 20, 60, and 70% for methionine + cystine, threonine, tryptophan, isoleucine, and valine, respectively. In Trials 1 and 2, feed was given in four meals per day, whereas, in Trial 3, two feeding frequencies (two and seven meals per day) were compared. Five or six N and energy balance (indirect calorimetry) measurements were conducted for each treatment, and components of heat production were estimated. Results of Trial 3 showed no effect of meal frequency on either N or energy utilization. Reduction of dietary CP content had no effect on N retention or animal performance but markedly decreased N excretion (-40% in Trials 2 and 3, and -58% in Trial 1). In the three trials, the lower N excretion with low-CP diets was accompanied by a reduction in urinary energy loss equivalent to 3.5 kJ/g of decrease in protein intake. Data of the three trials indicated that heat production was lower when CP was reduced (-7 kJ/g decrease in protein intake). This lower heat production was attributed to a reduction of the thermic effect of feed, whereas heat production associated with physical activity and maintenance were not affected. Reduction of dietary CP was associated with higher energy gain, mainly as fat. But, this effect was no longer significant when data were adjusted for similar NE intakes. These results confirm the possibility of limiting N excretion, while maintaining a high level of performance, by reducing CP level in the feed with adequate AA supplementation. This study also confirms the superiority of the NE system (in comparison with DE or ME systems) for predicting performance and energy gain of pigs and controlling carcass adiposity, especially in situations of feeds with variable CP contents.     

Effects of dietary threonine and crude protein on growth performance, carcase and meat composition of broiler chickens

1. The aim of the study was to investigate the effects of dietary threonine (Thr) and crude protein (CP) in maize-soybean meal based diets on the growth performance, carcase traits and meat composition of broiler chickens and to determine the dietary Thr requirement for optimum performance (weight gain and feed conversion efficiency (FCE)) at 0 to 3 weeks and 3 to 6 weeks of age. 2. Two basal diets that differed in CP (191.3 or 179.7 and 176.7 or 165.4 g/kg at 0 to 3 and 3 to 6 weeks, respectively) were formulated to have identical contents of Thr (6.0 and 5.4 g/kg), energy (12.97 and 13.39 MJ ME/kg) and other essential amino acids except for Gly + Ser. Basal diets were supplemented with L-Thr from 0.6 to 1.8 g/kg in 0.6 g/kg increments. Broiler chicks (540) were randomly allocated to 9 dietary treatments with 6 replicates of 10 (5 female, 5 male) chicks. 3. A significant interaction between dietary CP and Thr was found for feed intake, body weight (BW) gain and FCE. Increasing Thr supplementation improved feed intake, BW gain and FCE, especially in high CP diets in both feeding periods. 4. Incremental increases in dietary Thr increased breast yield at both CP levels and drumstick yield only on high CP diets. The proportion of thigh decreased with Thr concentration. Liver weight was significantly reduced by Thr supplementation; abdominal fat was not affected. 5. Estimated Thr requirements for FCE increased as dietary CP increased according to an exponential model. This model indicated higher Thr requirements than those of broken-line models for growth performance.     

Nitrogen balance in barrows fed low-protein diets supplemented with essential amino acids

This study was conducted to determine the effect of addition of essential amino acids (EAA) to low-protein diets on N balance in barrows. Thirty barrows (Duroc × Yorkshire) with an initial BW of 36 kg were fed 5 corn- and soybean meal-based diets containing 13.6 to 18.2% crude protein (CP) for 10 d in a randomized complete block design. The 18.2% CP diet was formulated without addition of EAA (Lys, Met or Thr). The other diets contained 13.6 to 16.5% CP and were supplemented with EAA to provide 0.83% true digestible lysine equal to that in the 18.2% CP diet. Fecal, urinary, and total N excretion as well as N retention (g/d) decreased with decreasing dietary CP level (P < 0.01). The apparent digestibility of N was almost the same for the 18.2 and 16.5 CP diets, but the value was 2% higher (P = 0.07) than that for the 13.6% CP diet. These findings indicate that, compared with the 18.2% CP diets, supplementation with three EAA to the lowest-protein diets (13.6 CP) is inadequate for maximum intestinal protein digestion, amino acid absorption, or tissue protein deposition in growing barrows.     

Ruminal degradability and intestinal digestibility of individual amino acids in mixed diets with different crude protein levels measured by the modified in vitro three‐step and mobile nylon bag technique

The ruminal degradability and intestinal digestibility of dry matter (DM), crude protein (CP) and amino acids (AA) in three total mixed rations with different CP levels were estimated using the modified in vitro three‐step procedure (TSP) and mobile nylon bag (MNB) technique on growing lambs. The ruminal effective degradability of DM and CP did not respond with increasing dietary CP level. However, the intestinal digestibility of DM was significantly increased with increasing dietary CP level estimated by TSP (P < 0.05) or MNB method (P < 0.01). Intestinal digestibility coefficients of CP determined by TSP were lower than those of the MNB method. Histidine was extensively degraded by rumen micro‐organisms, while tyrosine was the most anti‐degradable AA among the samples. The ruminal AA degradability exhibited no significant differences except for threonine, tryptophan, alanine, aspartic acid and proline for the three diets. Similarly, only a few AAs (i.e. histidine, methionine, tryptophan, aspartic acid and cysteine in TSP; histidine, tryptophan, aspartic acid and serine in MNB) had significant differences in their intestinal digestibility; in addition, values of MNB were lower than that of the TSP method, indicating that intestinal digestibility of DM seems to be overestimated in TSP, while that of CP might be overestimated in the MNB method.     

Impact of dietary crude protein and amino acids status on performance and some excreta characteristics of broiler chicks during 10–28 days of age

A study was conducted in a completely randomised design to evaluate the effects of providing almost all important essential amino acids (EAA) in low‐crude protein (CP) diets equal to that of higher CP diets in broiler chickens. Also the effects of additional mixture of glycine (Gly) and glutamic acid (Glu) or supplementation of excess EAA to low‐CP diets on the live performance and excreta characteristics including pH, moisture, nitrogen, uric acid and ammonia concentration were measured to ascertain the optimum CP concentration for the maximum performance and reduced excreta ammonia concentration. Male, broiler chickens growing from 10 to 28 days of age were fed eight experimental diets. Reducing dietary CP below 19% negatively affected performance. Adding the Gly and Glu mixtures to 17% CP diets improved live performance. Reducing CP to 19% with a normal amino acids status declined N, ammonia, uric acid, moisture and pH of excreta significantly. These findings suggest that diminishing dietary CP from 23% to 19% while maintaining adequate EAA levels during 10–28 days of age results in not only a significant decline in N emission, but also a probable reduction in the NH₃ volatilisation because of reduction in pH and moisture. Contrary to expectations, reduction of dietary CP below the minimum level (19%) resulted in more ammonia. All these factors may improve on litter and air quality within the housing facility and reduce the ventilation rate required to emit the elevated ammonia gas concentrations.     

Effect of the ratio between essential and nonessential amino acids in the diet on utilization of nitrogen and amino acids by growing pigs.

In 36 growing pigs (30 to 60 kg), N balance and amino acid (AA) composition of weight gain were measured to evaluate the interactive effect of the ratio between N from essential amino acids (EAA(N)) to nonessential amino acids (NEAA(N)) and total N level (T(N)) in the diet on N retention and utilization of N, EAA(N), NEAA(N), and AA. Nine diets composed from ordinary feedstuffs and supplemented with crystalline AA were used (three EAA(N):NEAA(N) ratios of 38:62, 50:50, and 62:38 at three T(N) levels of 18.8, 22.9, and 30.0 g/kg). Pigs were fed restrictedly, at a level of 2.8 x energy for maintenance. In all diets, EAA (including arginine) supply was according to or slightly above the recommended ratios to lysine. Measurements were done in four blocks of nine pigs each. In a concomitant slaughter experiment, the AA composition of deposited body protein was determined to estimate AA utilization. The effects of T(N) and EAA(N):NEAA(N) and their interaction for N retention and utilization were significant. Nitrogen retention increased with higher T(N) in the diet. Increasing EAA(N):NEAA(N) from 38:62 to 50:50 improved N retention only at the two lower T(N) levels. Increasing EAA(N): NEAA(N) above 50:50 failed to improve N retention significantly at any of the three T(N) levels. Lowering T(N) improved the utilization of total and digested N and of EAA(N) and NEAA(N). The increase in EAA(N): NEAA(N) consistently resulted in a lower utilization of EAA(N), but this was compensated by a higher utilization of NEAA(N). The utilization of T(N) was improved by increasing EAA(N):NEAA(N) from 38:62 to 50:50 at the two lower T(N) levels and was relatively unaffected by EAA(N):NEAA(N) at the highest T(N). However, a lower utilization of N was observed at a ratio of 62:38 at a T(N) level of 22.9 g/kg. The effects were similar for utilization of individual EAA and NEAA. Utilization of alanine, aspartic acid, and glycine was close to or >100% at the highest EAA(N):NEAA(N), which was expected because all of these AA are synthesized in pigs. Also, the utilization of arginine was >100% in most of the treatments, which confirms the semiessential character of this AA for maintenance. We concluded that the required ratio of EAA(N):NEAA(N) for optimal N retention and utilization is approximately 50:50. The EAA(N):NEAA(N) is more important at lower dietary protein levels. This study indicates that EAA(N): NEAA(N) can be increased up to 70:30 without lowering the utilization of N. Thus, deaminated EAA(N) was efficiently utilized for the synthesis of NEAA(N).     

低蛋白质补充合成氨基酸饲粮对肉仔鸡生长性能、氮排泄及胴体品质的影响

本研究分2个试验,旨在探讨低蛋白质补充合成氨基酸饲粮对肉仔鸡生长性能、氮排泄和胴体品质的影响.试验1选用600只1日龄爱拔益加肉仔鸡(公母各占1/2),分1～21 d,22～42 d和43～49 d 3个阶段饲养,饲粮共设5个处理,粗蛋白质水平分别为:生长前期(1～21 d):22.8%、21.9%、21.0%、19.5%和19.0%;生长中期(22～42 d):20.1%、18.8%、17.8%、16.5%和16.0%;生长后期(43～49 d):18.0%、16.9%、15.9%、15.0%和13.8%.各个处理蛋氨酸、赖氨酸和苏氨酸水平均满足NRC(1994)肉仔鸡营养需要.试验2的5组肉鸡饲粮的蛋白质水平与试验1的生长前期和生长中期饲粮相同,同时补充了足够的合成氨基酸以满足肉仔鸡对所有可消化必需氨基酸的需要量.结果表明:降低饲粮粗蛋白质水平同时补充合成氨基酸不影响试验1各个阶段肉仔鸡的生长性能(P>0.05).当以可消化氨基酸为基础配制饲粮时(试验2),生长前期肉仔鸡的日增重和饲料转化效率得到显著改善(P<0.01),但生长中期和生长全期肉仔鸡日增重和饲料转化效率差异不显著(P>0.05).降低饲粮粗蛋白质水平线性增加了试验1中肉仔鸡的脂肪沉积率(P<0.05),但对其他胴体指标没有显著影响(P>0.05).氮排泄随饲粮粗蛋白质水平的降低而线性减少(P<0.01).此外,降低饲粮粗蛋白质水平还降低了试验2中肉仔鸡血浆甘氨酸和苯丙氨酸的含量(P<0.05).综上所述,降低肉仔鸡饲粮粗蛋白质水平同时补充合成氨基酸可获得使用高蛋白质饲粮时的生长性能和胴体品质.     

Influence of the ratio of essential to non essential amino acids on performance and carcase composition of the broiler chick

Male broilers were fed on isocaloric diets containing 140, 180 or 220 g/kg crude protein from 1 to 3 weeks of age. Four diets were formulated for each protein concentration so that essential amino acids (EAA), all balanced in proportion to requirement, supplied 350, 450, 550 or 650 g/kg crude protein. Weight gain, efficiency of food utilisation and total carcase protein reached plateaux at 550 g EAA/kg protein irrespective of the dietary protein content, whereas the proportion of carcase fat decreased and that of carcase protein increased as the proportion of EAA in the dietary protein increased. All EAA in the diet containing 550 g EAA/kg protein were supplied at 125% of requirement, suggesting that the amino acid requirements as reported are inaccurate. Weight gain and carcase protein were shown to be significantly (P less than 0.001) dependent on total intake of EAA rather than on the proportion of EAA in the diet per se. In order to supply sufficient EAA for maximum gains, the diet had to contain more than 140 g crude protein/kg and 450 g EAA/kg protein.