Influence of dietary lysine concentration on the oxidation of an indicator amino acid by growing boars

The influence of dietary lysine concentration on the oxidation of 14C-phenylalanine by growing boars was determined. Forty-five crossbred boars (30 to 40 kg) were fed a ground corn diet fortified with crystalline L-lysine to provide .28, .50, .85, 1.00, 1.25 and 1.54% total lysine. All other essential amino acids were supplemented to provide 135% of NRC (1979) recommendations. Release of 14CO2 from L-[1-14C]-phenylalanine was measured for 1 h following a meal of the experimental diet, which contained 20 mu Ci 14C-phenylalanine. Increasing dietary lysine concentration from .28 to .85% decreased 14CO2 production. Regression analysis of the data using a two-phase linear regression crossover model indicated that phenylalanine oxidation was minimized at a dietary lysine concentration of .65%. It was concluded that a concentration of .65% lysine minimized the oxidation of amino acids and provided them as possible substrates for protein deposition. The oxidation of an indicator amino acid can, therefore, be used to determine the effect of dietary lysine concentration on the partition of amino acids between metabolic fuels and body protein.     

Effect of low levels of dietary tyrosine on the hair colour of cats

Experiments were conducted to investigate the basis for the change in hair colour of black cats to reddish-brown. Black cats were given purified diets based on gelatin, casein plus lactalbumin, or crystalline amino acids as protein sources. Diets that caused the colour of hair to change to reddish-brown were associated with a reduction in melanin in hair (observed by direct microscopic examination), a decreased total melanin concentration and low concentrations of tyrosine in plasma. Reddish hair coat was induced in black kittens born to queens given a tyrosine-deficient diet during pregnancy. Black hair colour was maintained or restored by diets containing a high concentration of tyrosine or phenylalanine. Current dietary recommendations for dietary tyrosine and phenylalanine for cats are below those required to support maximal melanin synthesis in black cats. The requirement appears to be greater than a combination of 4.5 g tyrosine plus 12 g phenylalanine/kg diet but less than 24 g phenylalanine alone/kg diet.     

The effect of diarrhea on the oxidation of 14C-phenylalanine in piglets receiving diets varying in protein and proline concentration.

The oxidation rate of L-[1-14C]phenylalanine in piglets suffering from diarrhea and receiving diets varying in concentration of protein or proline was compared to the oxidation rates in healthy animals. Phenylalanine oxidation was used to indicate the partition of absorbed amino acids between protein synthesis and oxidation. Piglets receiving adequate protein diets and suffering from diarrhea oxidized significantly more phenylalanine (P less than 0.001) than healthy piglets. Piglets receiving additional proline and with symptoms of diarrhea oxidized phenylalanine at rates 50 to 70% higher than healthy piglets. The results show that piglets with diarrhea are less able to retain absorbed amino acids for protein synthesis than healthy pigs. The reduced nitrogen retention commonly observed in animals with diarrhea may be partly explained by the increased catabolism of absorbed amino acids.     

Effects of 4,4'-dimethyldiphenyliodonium chloride on performance of growing cattle

Two 112-d studies were conducted to evaluate effects of the deaminase inhibitor, 4,4'-dimethyldiphenyliodonium chloride, on performance of growing cattle. With diets containing low levels of crude protein (i.e., 11%), 25 ppm of chemical in the diet increased (P less than .05) gain and improved (P less than .05) feed efficiency. Feed intake was not affected. Higher levels of chemical (50 and 100 ppm) produced equivalent responses. With a higher level of dietary crude protein (i.e., 14%) gain and feed efficiency were not improved and some decreases in feed intake were observed. Performance responses resulting from adjustments in ruminal nitrogen transactions to provide more alpha-amino-N depend upon whether the animal needs additional amino acids for maintenance and production. Our data demonstrated that the supply of amino acids can be increased either by adjustment of ruminal nitrogen transactions with a chemical agent or by increasing concentration of dietary protein.     

Tryptophan requirement of growing pigs at various body weights

The purpose of this study was to determine the tryptophan (Trp) requirement of growing pigs at different body weight (BW) ranges. Three performance experiments were conducted with female pigs in the BW ranges of 25-50, 50-80 and 80-115 kg. In addition to the performance experiments, nitrogen balance experiments were carried out in which pigs weighing 56, 66 and 86 kg were used. Trp-deficient basal diets were formulated to which varying amounts of l-Trp were added. The amino acid concentrations of the diets were analysed; concentrations of standardized digestible amino acids were calculated on the basis of tabular values. The calculated concentrations of standardized ileal digestible tryptophan were 0.81, 1.11, 1.41, 1.71, 2.01 g/kg diet in the lower BW range (25-50 kg), 0.71, 0.96, 1.21, 1.46, 1.71 g/kg diet in the middle BW range (50-80 kg), and 0.49, 0.69, 0.89, 1.09, 1.29 g/kg diet in the upper BW range (80-115 kg). Dose-response relationships were evaluated by means of an exponential regression model. In all three age ranges, performance parameters as well as nitrogen retention were strongly influenced by the dietary concentration of standardized ileal digestible tryptophan. According to the exponential model, in the 25-50 kg BW range, 95% of the maximum feed consumption, BW gain and nitrogen retention were achieved at concentrations between 1.96 and 2.00 g of standardized ileal digestible Trp per kilogram diet, corresponding to 3.32-3.39 g/day. In the BW range of 50-80 kg, 95% of the maximum of these parameters occurred at concentrations of standardized ileal digestible tryptophan in excess of the highest concentration of 1.71 g/kg diet, corresponding to 3.71 g/day. In the BW range of 80-115 kg, 95% of the maximum of BW gain and nitrogen retention were recorded at concentrations of 1.22 and 0.84 g standardized ileal digestible Trp per kilogram diet, corresponding to 3.77 and 2.25 g/day, respectively. Related to the energy value of the diets, the optimal concentration of standardized ileal digestible tryptophan are between 140 and 143 mg/MJ metabolizable energy (ME) in the BW range of 25-50 kg, in excess of 127 mg/MJ ME in the BW range of 50-80 kg and between 62 and 90 mg/MJ ME in the BW range of 80-115 kg. In conclusion, it is suggested that the requirement of standardized ileal digestible tryptophan for growing pigs might be higher than currently assumed.     

Tryptophan and threonine requirements of young pigs and their effects on serum calcium, phosphorus and zinc concentrations

Four 28-d trials were conducted using a total of 432 pigs, with average initial weight across trials ranging from 6.3 to 9.7 kg, to estimate the tryptophan (trials 1 and 2) and threonine (trials 3 and 4) requirements of pigs fed low protein, corn-sunflower meal diets. The effect of tryptophan, threonine and protein level on serum calcium, phosphorus and zinc also was studied. The diets contained either 12 or 13% protein and were calculated to be adequate in all nutrients except crude protein and the amino acid being investigated. A lysine supplemented, 18% protein, corn-sunflower meal diet was included in all trials as a positive control. In trial 1, weight gains of pigs increased linearly (P less than .005) while feed conversion improved cubically (P less than .05) as dietary tryptophan increased from .14 to .22%. Pigs fed the 18% protein diet gained faster (P less than .05) and required less feed/gain than pigs fed low protein diets. In trial 2, weight gains improved quadratically (P less than .005) and feed conversion improved linearly (P less than .05) as dietary tryptophan increased from .104 to .204%. Serum phosphorus and zinc concentrations were lower (P less than .05) in pigs fed the 18% protein diet. In both trials, serum urea N responded quadratically (P less than .05) to increasing dietary tryptophan, and was lower (P less than .05) in pigs that were fed diets supplemented with L-tryptophan than in those fed the low protein basal or 18% protein diets.(ABSTRACT TRUNCATED AT 250 WORDS)     

Increasing dietary crude protein does not increase the essential amino acid requirements of kittens

Essential amino acid (EAA) requirements of omnivores and herbivores (e.g. chicks, lambs, pigs and rats) are directly related to the concentration of dietary crude protein (CP). When an EAA is limiting in the diet, addition of a mixture of EAA lacking the limiting one (which increases dietary CP) results in a decrease in food intake and weight gain. This interaction has been referred to as an AA imbalance and has not been studied in depth in strict carnivores. The objectives of these experiments were to examine the effects on growing kittens (2-week periods) of the addition to diets of a mixture of AA lacking the limiting one. The control diets were at the requirement of the respective limiting EAA (or about 85% of the 1986 National Research Council requirement). In experiment 1, with the dietary EAAs at the minimally determined requirements, the concentration of the essential or dispensable amino acids was increased to determine if CP or an EAA was limiting. Results of growth rates (n = 12) and plasma AA concentrations indicated that tryptophan was limiting, but increased body weight gain also occurred when the concentration of CP was increased as dispensable amino acids without additional tryptophan. Experiment 1 was repeated in experiment 2 using a crossover design. Again, when tryptophan was limiting additional concentrations of dispensable AAs increased body weight gain. This response is the opposite of that in herbivores and omnivores. Experiment 3 consisted of 10 separate crossover trials, one for each of the 10 EAA and examined the effect of two concentrations of dietary CP (200 and 300 g CP/kg diet) on body weight gain of kittens (n = 8) offered diets limiting in each respective EAA. Body weight gain was numerically greater when diets contained 300 g CP/kg than 200 g CP/kg for eight of 10 EAAs (p < 0.05 for only isoleucine and threonine) when each amino acid was limiting. This response is the reverse of that which occurs in chicks, lambs, pigs and rats when an EAA is limiting and dietary CP lacking the limiting EAA is increased. These results indicate that the EAA requirements of kittens are not positively correlated with dietary CP concentrations.     

Amino acid requirements of growing chickens.

1. Using 18% protein diets (N times 6-25), consisting mainly of conventional ingredients of known amino acid composition, the amino acid requirements as percentages of diet and of dietary protein respectively for broiler chickens between 14 and 28 d of age were found to be: threonine 0-50-0-52% of diet (2-8-2-9% of dietary protein); glycine 0-48-0-50 (2-7-2-8); valine 0-69-0-71 (3-8-3-9); methionine+cystine 0-58 (3-2); isoleucine smaller than 0-48 (smaller than 2-7); leucine smaller than 1-05 (smaller than 5-8); tyrosine+phenylalanine 1-09-1-12 (6-1-6-2); lysine 0-87 (4-8); histidine smaller than 0-34 (smaller than 1-9); arginine smaller than 0-76 (smaller than 4-2); tryptophan smaller than 0-14 (smaller than 0-78). 2. Values found were in general lower than those determined using diets consisting entirely of purified amino acids and the reasons for this are discussed.     

Effect of deficiencies of single essential amino acids on nitrogen and energy utilisation in chicks.

1. Diets 50% deficient in single essential amino acids were fed to chicks from day 8 to day 18 after hatching to evaluate body-weight gain, food consumption, body composition, nitrogen (N) and energy utilisation. 2. Body-weight gain was reduced most severely by deficiency of isoleucine followed in decreasing order by threonine, arginine, valine, histidine, tryptophan, methionine plus cystine, phenylalanine plus tyrosine, leucine and lysine, and possible reasons for the differences are discussed. 3. Body-weight gain and food efficiency were highly correlated with food consumption but metabolisable energy value of diets was not affected by single essential amino acid deficiencies. 4. Generally N retention (N retained/N consumed) and energy retention (energy retained/energy consumed) reflected food consumption, except for a lower N retention by chicks fed on the methionine plus cystine-deficient diet and for a lower energy retention by chicks fed on the valine deficient diet. 5. The amino acid deficient in the diet was present at very low concentration in the blood plasma.     

Methionine requirement of the finishing pig

Two pig experiments were conducted using a methionine (Met)-deficient feather meal-corn-soybean meal basal diet (13% CP; 3,400 kcal ME/kg diet, .126% Met, 456% cystine) supplemented with an amino acid mixture (lysine, tryptophan, histidine, threonine and phenylalanine) to determine the Met requirement of finishing pigs between 50 and 80 kg live weight. Using young chicks in a Met bioavailability growth assay and cecectomized adult cockerels in a Met digestibility assay, the Met-deficient basal diet was found to contain .115% bioavailable and .110% digestible Met. These results gave a bioavailability estimate (relative to DL-Met set at 100%) of 91.3 +/- 2.5% and a true digestibility estimate of 87.0 +/- 2.2% for Met in the basal pig diet. In Exp. 1, 21 crossbred pigs averaging 61 kg initially were individually fed diets containing .115, .165 or .215% bioavailable Met for 21 d. Average daily gain and gain:feed ratio increased quadratically (P less than .05) as level of Met increased. In Exp. 2, 30 crossbred pigs averaging 53 kg were individually fed diets containing .115, .135, .155, .175 or .195% bioavailable Met for 27 d. Daily gain and gain;feed ratio responded linearly (P less than .01) as Met level increased. Based on the results of Exp. 2, the bioavailable Met requirement of finishing pigs in the weight range 50 to 80 kg was estimated to be .182% of the diet. Assuming an 88% bioavailability of Met in commercial diets based on corn and soybean meal, the total Met level needed in practice would be .207%. If 55% of the finishing pig's sulfur amino acid need can be furnished by cystine, the total sulfur amino acid requirement would be .45% of the diet.     

Performance and nutrient balance in growing swine fed low-protein diets supplemented with amino acids and potassium

Five experiments, using 216 barrows and gilts (initial weight 19.9 to 23.7 kg), were conducted to evaluate the effects of improving amino acid balance by supplementing low-protein corn-soybean meal diets with essential amino acids. Three experiments were growth studies lasting approximately 3 wk, and the other two were 4-d metabolism trials. The control diets in each of the experiments were formulated to contain .80% lysine and contained approximately 17% CP. The other diets were formulated from a basal diet containing a 10.9% CP, fortified corn-soybean meal mixture, which included crystalline L-lysine.HCI, L-tryptophan, L-threonine, L-isoleucine, DL-methionine and L-valine to correct amino acid deficiencies. Nonessential N (glutamic acid or urea) also was added to some of the diets to increase the CP equivalent to 12 or 13%. Supplemental K (as a salt of bicarbonate or glutamate) was included in selected diets to increase the K concentration to the same level as that of the control diet. Growth rate of pigs fed the basal diet was similar (P greater than .05) to that of the control diets in only one growth study. Added glutamic acid and urea did not improve either growth rate or N retention. Added K improved K digestibility but did not increase K retention, N retention or growth rate. Improving amino acid balance by adding essential amino acids to low-protein diets did not benefit performance beyond that of a typical corn-soybean meal diet. Under our conditions, K, N, and nonessential N were not limiting.     

Efficiency of amino acid utilization in the growing pig at suboptimal levels of intake: lysine, threonine, sulphur amino acids and tryptophan

A series of N balance experiments using growing pigs was conducted to study the efficiency of utilization of lysine, threonine, sulphur amino acids and tryptophan and to estimate their maintenance requirements. Purified diets based on casein and crystalline amino acids as the sole source of N contained graded levels of each amino acid, corresponding to expected protein accretion rate of 0, 33, 66, 99 and 132 g/day, respectively. N retention increased linearly (p < 0.01) as the dietary concentration of the limiting amino acid increased. Based on linear regression equations relating amino acid deposition in body protein to amino acid intake, marginal efficiencies of ileal digestible amino acid utilization were calculated to be lysine 0.91, threonine 0.83, sulphur amino acids 0.85 and tryptophan 0.66. Extrapolating the regression equations to zero N retention, the daily requirements of amino acids for N equilibrium were estimated to be (mg/kg(0.75)) lysine 39, threonine 49, sulphur amino acids 46 and tryptophan 16.     

Efficiency of amino acid utilization in the growing pig at suboptimal levels of intake: branched-chain amino acids, histidine and phenylalanine + tyrosine

Five balance experiments on growing pigs were carried out to study the marginal efficiency of utilization of isoleucine, leucine, valine, histidine and phenylalanine + tyrosine and to estimate their requirements for maintenance. Purified diets based on casein and crystalline amino acids as the sole source of N contained graded levels of each amino acid, corresponding to protein accretion rates of 0, 33, 66, 99 and 132 g/day, respectively. All other essential amino acids were given in a 30% excess. N retention increased linearly (p < 0.01) as the dietary concentration of the limiting amino acid increased. Based on linear regression equations relating amino acid deposition in body protein to amino acid intake, marginal efficiencies of ileal digestible amino acid utilization were calculated to be isoleucine - 0.81, leucine - 0.81, valine - 0.82, histidine - 1.17 and phenylalanine + tyrosine - 0.67. Extrapolating the regression equations to zero N retention, the daily requirements of amino acids for N equilibrium were estimated to be (mg/kg0.75) isoleucine - 18, leucine - 33, valine - 23, histidine - 14 and phenylalanine + tyrosine - 43.     

Dietary crude protein concentration does not affect the leucine requirement of growing dogs

The objective of the present study was to examine the interaction between graded levels of leucine and dietary crude protein. Dose–response curves were generated using four 3 × 3 Latin squares (two dogs/square). Each square represented one of two concentrations of crude protein (140 or 280 g/kg diet) and one of two combinations of three concentrations of leucine (5.0, 7.0 and 9.0 g/kg diet or 9.0, 11 and 13 g/kg diet). An additional experiment was performed by feeding crude protein at 210 g/kg diet with either 7.0 or 11 g leucine/kg diet. Weight gain, food intake, nitrogen retention, plasma albumin and plasma amino acids were measured. The requirement was determined to be the minimum leucine concentration required to maximize weight gain and nitrogen retention. For 8–14-week-old male Beagle dogs, 140 g crude protein/kg diet in a diet containing 18 kJ metabolizable energy/g does not appear to support maximal growth. The leucine requirement was not affected by doubling the dietary crude protein level from 140 to 280 g/kg diet. From these results, the leucine requirement of 8–14-week-old Beagle dogs appears to be 11 g leucine/kg diet independent of the level of dietary crude protein, whereas dogs over 14 weeks require only 7 g leucine/kg diet for maximal nitrogen retention.     

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.     

Tryptophan availability of some feedstuffs determined by pig growth assay

Three experiments were conducted with young pigs to measure the availability of tryptophan in soybean meal, meat and bone meal, cottonseed meal, corn and sorghum. In Exp. 1, a 17.5% crude protein corn and gelatin-based diet, deficient in tryptophan, was supplemented with graded levels of L-tryptophan to establish the growth response of 10- to 20-kg pigs to graded additions of dietary tryptophan. From these data the requirement for maximal growth was calculated to be .16% of the diet using a broken-line model. In Exp. 2, the effects of excess amino acids in a test feedstuff, i.e., soybean meal, on the growth assay method for estimating tryptophan availability was evaluated. The addition of excess crystalline amino acids to the basal diet in proportions equal to the excesses contributed by a test level of soybean meal resulted in a 17.7 percentage unit reduction in the estimate of tryptophan availability (82.3%). When the standard diet was supplemented with amino acids to provide the pattern of excess amino acids found in the corn-gelatin basal diet with added soybean meal, the availability of tryptophan in soybean meal was estimated to be 95.2%. In Exp. 3, the tryptophan availabilities for meat and bone meal, cottonseed meal, corn and sorghum were estimated to be 82.2%, 80.9%, 94.0% and 86.4%, respectively. The diets used in this experiment were supplemented to contain excesses of individual amino acids in the same proportions as found in the basal diet, with the test feed ingredient added as a source of tryptophan. In these experiments the tryptophan content of the various feedstuffs was measured by ion-exchange liquid chromatography following alkaline hydrolysis.     

Postprandial oxidative losses of free and protein‐bound amino acids in the diet: interactions and adaptation

Postprandial oxidation of dietary free amino acids or egg white protein was studied using the [¹³CO₂] breath test in rats, as well as in humans. Thirty‐eight male rats were assigned to four dietary test groups. Two diets only differed in their protein fraction. Diet I contained 21% egg white protein. For the breath test egg white protein, intrinsically labelled with [1‐¹³C]‐leucine, was used as a substrate. Diet II contained the same amino acids as diet I, though not as egg white protein but in free form. Free [1‐¹³C]‐leucine was used to label this diet. In addition, two 1:1 mixtures of both diets were used. During the breath test either the free amino acid or the protein fraction was labelled as in diets I or II. The animals were breath‐tested following short‐term (day 5) and long‐term adaptation (day 20) to their experimental diet. For all diets, including the mixed diets, postprandial oxidative losses on day 5 were significantly higher for the free leucine compared with the protein‐derived leucine. Differences between free and protein‐derived leucine oxidation had, however, largely disappeared on day 20. The human subjects were breath‐tested without any adaptation period to the diets. The oxidative losses of free leucine were also higher than those of protein‐derived leucine. None of the studies showed any indication for an interaction between the oxidation of protein‐derived amino acids and free amino acids. It is concluded that free and protein‐derived amino acids in the diet are mainly metabolized independently.     

The amino acid requirements of the growing chick. I. Determination of amino acid requirements

The amino acid requirements of the growing chick have been determined using a diet based on soybean meal and maize meal. The diet contained 18% protein (N% x 6.25, dry matter basis) made up to 14% contributed by conventional ingredients and 4% protein equivalent in the form of amino acids. Starting with a diet formulated to meet the reference levels recommended by Dean and Scott (1965) a programme of experiments was carried out to improve this amino acid balance. The results indicated that the growing chick requires not more than 0.53% threonine, 0.61% glycine, 0.79% valine, 0.62% isoleucine, 1.34% leucine, 0.75% phenylalanine (or 1.3% phenylalanine plus tyrosine), 0.85 % lysine, 0.4% histidine, 0.86% arginine, 0.17% tryptophan and 0.39% methionine (or 0.79% methionine plus cystine).     

Effect of dietary electrolyte balance on growth and acid-base status in swine

The effect of dietary electrolyte balance on pigs fed lysine- or tryptophan-adequate or tryptophan-deficient diets was investigated in four experiments using 8- to 12-wk-old pigs. Electrolyte balance, expressed as Na+K-Cl in meq/kg of diet, was varied by altering dietary levels of Na and Cl while holding all other minerals constant. In two experiments in which the basal diet contained a balance of 135 meq/kg, simple lysine or tryptophan deficiences caused depressed growth, feed intake and efficiency of feed utilization, but none of these responses was altered by dietary supplementation with NaHCO3. In one experiment in which the electrolyte balance of the basal diet was 61 meq/kg and in which both lysine and tryptophan were limiting. NaHCO3 supplementation significantly increased growth and feed intake. This did not occur if the diet was also supplemented with tryptophan. A final experiment was conducted to determine the response of pigs to a range of electrolyte balance (-85 to 341 meq/kg) in a practical corn-soy diet containing adequate levels of all amino acids. Growth and feed intake appeared to be maximal for balances of 0 to 341 meq/kg Na+K-Cl, but were decreased at -85 meq/kg (P less than .05). Acid-base balance was adversely affected at 0 meq/kg. The results suggest that the response of lysine-deficient pigs to sodium bicarbonate is dependent upon the electrolyte balance of the diet, and also is influenced by other dietary amino acids.     

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.