Histidine Requirement Research Articles

Effect of dietary histidine on contents of carnosine and anserine in muscles of broilers.

Carnosine (β-alanyl-L-histidine) and anserine (β-alanyl-1-methyl-L-histidine) are dipeptides mainly found in skeletal muscle and brain of many vertebrates, and particularly high concentrations are observed in chicken pectoral muscles. It was reported that these peptides have many functions, such as antioxidant activity. In this study, we examined the effect of different levels of dietary histidine on carnosine and anserine contents in broiler muscles. The 14-days-old female Chunky strain broilers were given feeds containing three different levels of histidine; 67% (Low-His), 100% (Control) and 200% (High-His) of histidine requirement according to the NRC (1994). Chicks were fed experimental diets for 10 days. Both dipeptides in muscle were significantly decreased. In particular, carnosine was not detected at all in the Low-His group and was significantly increased in the High-His group. Both dipeptides were not detected in plasma. These results indicated the possibility to produce chicken meat with enhanced amount of these dipeptides by high histidine feeding.

Dietary histidine requirement of fingerlingCatla Catla(Hamilton) based on growth, protein gain, histidine gain, RNA/DNA ratio, haematological indices and carcass composition

To investigate the histidine requirement of fingerling Catla catla (3.65 ± 0.15 cm; 0.65 ± 0.36 g), six casein-gelatin based diets (33% CP; 13.58 kJ g−1 DE) containing graded levels of L-histidine (0.25%, 0.39%, 0.53%, 0.67%, 0.83%, 0.96% of the dry diet) were fed near to satiation thrice a day for 12 weeks. Maximum absolute weight gain (AWG; 8.63 g fish−1), protein gain (PG; 1.45 g fish−1), histidine gain (HG, 48.19 mg fish−1), RNA/DNA ratio (4.15), best feed conversion ratio (FCR; 1.31), highest haemoglobin (Hb, 9.61 g dL−1), RBCs (2.84 × 106 mm−3) and haematocrit (Ht, 30.12%) were recorded in fish fed diet containing 0.67% histidine. However, broken-line regression analysis of AWG, PG, HG, RNA/DNA ratio, FCR, Hb, Ht and RBCs against dietary histidine reflected the histidine requirement at 0.65%, 0.64%, 0.63%, 0.68%, 0.63%, 0.66%, 0.68% and 0.65% dry diet respectively. Carcass protein was found to improve significantly (P < 0.05) from 13.36% to 16.42% with the increase in dietary histidine from 0.25% to 0.67%. Based on regression analysis of AWG, PG, HG, RNA/DNA ratio, FCR, Hb, Ht and RBCs, it is recommended that the diet for fingerling catla should contain histidine in the range of 0.63–0.68% dry diet, equivalent to 1.91–2.06% of the dietary protein for optimum growth, feed utilization, blood profile and carcass composition.

Adult triploid Atlantic salmon (Salmo salar) have higher dietary histidine requirements to prevent cataract development in seawater

The study investigated cataract preventive effects of dietary histidine (His) supplementation in triploid Atlantic salmon during seawater grow-out. Groups of individually PIT tagged diploid (2N) and triploid (3N) postsmolts were fed one of two supplemented dietary histidine levels; low (L, 12.6 g kg−1 diet) or high (H, 17.4 g kg−1 diet) from March to September following their first sea winter. Low severity cataracts were detected in both ploidy prior to supplemented His diet application. Thereafter, 3N-L showed progression of cataract development in the second spring-summer period, while development was inhibited in 3N-H. Severity of cataract showed a strong family effect. A positive correlation between initial triploid seawater growth (weight and TGC) under increasing water temperature and cataract severity was identified as a major risk factor. The relationship was reversed at harvest, where triploids were on average 7.5% smaller than their diploid siblings. Lens N-acetyl-histidine content reflected dietary His inclusion level and cataract severity, although no significant differences in lens His content were evident between ploidy or dietary groups. Results indicate that triploid Atlantic salmon appear to have a higher dietary histidine requirement than diploids and that preventative measures can be taken to mitigate further cataract development.

Dietary histidine requirement to reduce the risk and severity of cataracts is higher than the requirement for growth in Atlantic salmon smolts, independently of the dietary lipid source

The present study was carried out to investigate whether the dietary histidine requirement to reduce cataract development is higher than that for growth in Atlantic salmon smolts (Salmo salar L.) after seawater transfer and whether dietary vegetable oils contribute to cataractogenesis. Duplicate groups of salmon smolts were fed ten experimental diets with either fish oil (FO) or a vegetable oil (VO) mix replacing 70% FO and histidine at five target levels (10, 12, 14, 16 and 18g His/kg diet) for 13 weeks after seawater transfer. The VO diet-fed fish exhibited somewhat inferior growth and feed intakes compared with the FO diet-fed fish, irrespective of the dietary histidine concentration. Both cataract prevalence and severity were negatively correlated with the dietary histidine concentration, while lens N-acetyl-histidine (NAH) concentrations were positively correlated with it. The fatty acid profiles of muscle, heart and lens reflected that of the dietary oils to a descending degree and did not affect the observed cataract development. Muscle, heart and brain histidine concentrations reflected dietary histidine concentrations, while the corresponding tissue imidazole (anserine, carnosine and NAH) concentrations appeared to saturate differently with time. The expression level of liver histidase was not affected by the dietary histidine concentration, while the liver antioxidant response was affected in the VO diet-fed fish on a transcriptional level. The lowest severity of cataracts could be achieved by feeding 13·4g His/kg feed, independently of the dietary lipid source. However, the present study also suggests that the dietary histidine requirement to minimise the risk of cataract development is 14·4g His/kg feed.

Dietary Histidine Requirement for Juvenile Large Yellow Croaker, Pseudosciaena crocea R.

Dietary histidine requirements for large yellow croaker (initial average weight, 6.0 ± 0.10 g) were quantified by feeding isonitrogenous (crude protein 44%) and isocaloric (20 KJ/g) amino acid test diets with graded levels of histidine [0.45% (D1), 0.66% (D2), 0.78% (D3), 0.98% (D4), 1.24% (D5) and 1.40% (D6) of dry diet]. Each diet was randomly assigned to triplicate floating sea cages (1.0 × 1.0 × 1.5 m), 60 fish/cage. At the end of the 51 day experiment, the final weight (FW) and weight gain (WG) of large yellow croaker showed a positive correlation to increasing dietary histidine content (up to 0.78%), and thereafter declined. The growth of fish fed the D6 diet was significantly lower than fish maintained on the D2 and D3 diets; however, there were no significant differences in the growth of large yellow croaker among all the dietary treatments except D6. Fish fed the D3 diet had the highest FW and WG. The shift in feed efficiency (FE) values of fish fed D1 to D5 diets increased as dietary histidine content increased, and significantly decreased in fish fed the D6 diet. Based on the second-degree polynomial regression analyses of the growth data, optimum histidine requirement for juvenile large yellow croaker was 8.7 g/kg dry diet, (18.8 g/kg–20.8 g/kg of dietary protein within 95% confidence interval).

Multiple Genomic Changes Associated with Reorganization of Gene Regulation and Adaptation in Yeast

Frequently during evolution, new phenotypes evolved due to novelty in gene regulation, such as that caused by genome rewiring. This has been demonstrated by comparing common regulatory sequences among species and by identifying single regulatory mutations that are associated with new phenotypes. However, while a single mutation changes a single element, gene regulation is accomplished by a regulatory network involving multiple interactive elements. Therefore, to better understand regulatory evolution, we have studied how mutations contributed to the adaptation of cells to a regulatory challenge. We created a synthetic genome rewiring in yeast cells, challenged their gene regulation, and studied their adaptation. HIS3, an essential enzyme for histidine biosynthesis, was placed exclusively under a GAL promoter, which is induced by galactose and strongly repressed in glucose. Such rewired cells were faced with significant regulatory challenges in a repressive glucose medium. We identified several independent mutations in elements of the GAL system associated with the rapid adaptation of cells, such as the repressor GAL80 and the binding sites of the activator GAL4. Consistent with the extraordinarily high rate of cell adaptation, new regulation emerged during adaptation via multiple trajectories, including those involving mutations in elements of the GAL system. The new regulation of HIS3 tuned its expression according to histidine requirements with or without these significant mutations, indicating that additional factors participated in this regulation and that the regulatory network could reorganize in multiple ways to accommodate different mutations. This study, therefore, stresses network plasticity as an important property for regulatory adaptation and evolution.

Dietary amino acid l -histidine requirement of fingerling Indian catfish, Heteropneustes fossilis (Bloch), estimated by growth and whole body protein and fat composition

An eight-week feeding trial was conducted to determine the dietary histidine requirement of Indian catfish, Heteropneustes fossilis (6.20 ± 1.25 cm, 4.65 ± 0.48 g) in 75-L flow-through circular troughs. Six isonitrogenous (40%) and isoenergetic (17.90 kJ g−1) amino acid test diets with graded levels of l-histidine (0.25–0.75%, dry diet), in gradation of 0.10% histidine were formulated. Fish were randomly stocked in triplicate groups and fed experimental diets at 4% BW per day at 08:00 and 18:00 h. Maximum live weight gain (288%), best FCR (1.40) and PER (1.78) were occurred at 0.55% dietary histidine level. For the live weight gain, FCR, PER and body protein deposition data were examined using quadratic regression analysis, the breakpoints indicating requirements for histidine at 0.58, 0.54, 0.53 and 0.54% of dry diet, respectively. Significantly (P < 0.05) low moisture and higher whole body protein content were obtained in the 0.55% histidine diet, while body fat showed an increasing trend with the increase in dietary concentrations. Ash content remained insignificantly (P > 0.05) low among all dietary groups, except in diet I and diet II. Based on the above results, the recommended diet for young H. fossilis should contain histidine at 0.54% of dry diet, corresponding to 1.35% of dietary protein for optimum growth and efficient feed utilization.

Dietary histidine requirement of Singhi,Heteropneustes fossilisfry (Bloch)

Amino acids are vital for all living organisms including fish and histidine is an essential amino acid for fish. In view of this, dietary histidine requirement of fry Heteropneustes fossilis was determined by feeding casein–gelatin-based isonitrogenous (430 g kg−1 CP) and isocaloric (17.9 MJ kg−1 GE; 15.5 MJ kg−1 DE) amino acid test diets (10 to 20 g histidine kg−1 dry diet) to quadruplicate groups of randomly assigned fish to apparent satiety for 12 weeks. Maximum absolute weight gain (AWG; 44 g fish−1), protein retention efficiency (PRE; 20%), protein efficiency ratio (PER; 1.04), haemoglobin (Hb; 11.24 g dL−1), haematocrit (Hct; 35.11%), red blood count (RBCs; 2.98 × 109 mL−1) and lowest erythrocyte sedimentation rate (ESR; 1.92 mm h−1) were obtained at 16 g histidine kg−1 dry diet. The 95% maximum quadratic response of above data exhibited the requirement to be at 15.2, 15.1, 15.6 and 15.5 g histidine kg−1 diet. As histidine is found in higher concentration in haemoglobin, requirement obtained for Hct% and Hb is 4% greater than that required for maximizing weight gain and protein retention. Based on these results, dietary histidine requirement of H. fossilis fry is recommended between 15.1 and 15.6 g kg−1, corresponding to 35.1–36.3 g kg−1 protein.

Antimutagenic effects of compounds obtained from Eclipta alba linn. against strains of Salmonella typhimurium

In this experimental study, antimutagenic activity of compounds obtained from Eclipta alba Linn was screened by using Ames assay for detecting direct mutagenic activity and those requiring the metabolic activation. The crude compound extracted from Eclipta alba was considered as antimutagen and analyzed in this experiment. Two strains of Salmonella typhimurium, TA163 and TA96 were used to analyze the test. These two strains are confirmed as histidine requiring mutant strains. When the mutagen is added to the culture, the strain is mutated back, thereby loosing the histidine dependence for its growth. By this study, the crude compound of Eclipta alba prevents the strain to be mutated back to the non dependence for the genotyping of the Salmonella strains were performed by histidine requirement, rfa mutation analysis, UVrB mutation, R-factor analysis toxicity tests and antimutagenicity assay. The antimutagens obtained from the plant extract were determined for antimutagenic activity against direct acting mutagens and mutagen needing activation. For direct acting mutagens, NPD (N- nitro-o-phenyl diamine), MNNG (N- methyl-N-nitro-N-nitro soguanidine) and NaNa3 (sodium azide) with 1mg of the plant extract gives 98%, 95.2% and 90.7% inhibition the reverted colonies were observed whereas the mutagen needing activation 2-AAf (2-acetyl aminofluorine) gives 96.6% inhibition was observed. These above results indicated that the extract could inhibit the mutagenicity induced by direct acting mutagens as well as mutagens needing activation. Thus the extracts isolated from the test plant have possibility of antimutagenic activity of compound and further biochemicals extracted from the test plant will be analyzed.

Effects of dietary histidine levels on growth performance, body composition and intestinal enzymes activities of juvenile Jian carp (Cyprinus carpio var. Jian)

A total of 1200 juvenile Jian carp (Cyprinus carpio var. Jian) (8.76 ± 0.02 g) were fed diets containing graded levels of histidine at 2.3 (unsupplemented control), 4.4, 6.3, 8.6, 10.8 and 12.7 g kg−1 diet for 60 days to investigate the effects of histidine levels on growth performance, body composition, intestinal enzymes activities and microflora. Specific growth rate (SGR), feed efficiency, protein efficiency ratio, protein productive value, body protein content and lipid content of fish were lowest in fish fed the basal diet (P < 0.05). Activities of glutamate-pyruvate transaminase in muscle and hepatopancreas, trypsin, chymotrypsin, amylase, lipase activities in intestine and hepatopancreas, and Na+, K+-ATPase, creatine kinase, alkaline phosphatase, γ-glutamyl transpeptidase activities in three intestinal segments were improved by dietary histidine (P < 0.05), whereas glutamate-oxaloacetate transaminase activities and plasma ammonia content followed an opposite trend. The amounts of Lactobacillus, Escherichia coli and Aeromonas were significantly affected by dietary histidine levels (P < 0.05). These results suggested that histidine could improve growth and enhance intestinal enzymes activities of juvenile Jian carp. The dietary histidine requirement of juvenile Jian carp (8.76–68.02 g) based on SGR was 7.8 g kg−1 diet or 2.38 g 100 g−1 protein by quadratic regression analysis.

Interplay between Iron Homeostasis and the Osmotic Stress Response in the Halophilic Bacterium Chromohalobacter salexigens

In this study, the connection between iron homeostasis and the osmostress response in the halophile Chromohalobacter salexigens was investigated. A decrease in the requirement for both iron and histidine and a lower level of siderophore synthesis were observed at high salinity, and these findings were correlated with a lower protein content in salt-stressed cells. A six-gene operon (cfuABC-fur-hisI-orf6 operon) located downstream of the ectABC ectoine synthesis genes was characterized. A fur strain (in which the ferric iron uptake regulator Fur was affected) had the Mn resistance phenotype typical of fur mutants, was deregulated for siderophore production, and displayed delayed growth under iron limitation conditions, indicating that fur encodes a functional iron regulator. hisI was essential for histidine synthesis, which in turn was necessary for siderophore production. Fur boxes were found in the promoters of the cfuABC-fur-hisI-orf6 and ectABC operons, suggesting that Fur directly interacts with DNA in these regions. Fur mediated the osmoregulated inhibition of cfuABC-fur-hisI-orf6 operon expression by iron and functioned as a positive regulator of the ectABC genes under high-salinity conditions, linking the salt stress response with iron homeostasis. Excess iron led to a higher cytoplasmic hydroxyectoine content, suggesting that hydroxyectoine protects against the oxidative stress caused by iron better than ectoine. This study provides the first evidence of involvement of the iron homeostasis regulator Fur as part of the complex circuit that controls the response to osmotic stress in halophilic bacteria.

Protonation of Individual Histidine Residues Is Not Required for the pH-Dependent Entry of West Nile Virus: Evaluation of the “Histidine Switch” Hypothesis

Histidine residues have been hypothesized to function as sensors of environmental pH that can trigger the activity of viral fusion proteins. We investigated a requirement for histidine residues in the envelope (E) protein of West Nile virus during pH-dependent entry into cells. Each histidine was individually replaced with a nonionizable amino acid and tested functionally. In each instance, mutants capable of orchestrating pH-dependent infection were identified. These results do not support a requirement for any single histidine as a pH-sensing "switch," and they suggest that additional features of the E protein are involved in triggering pH-dependent steps in the flavivirus life cycle.

HISTIDINE REQUIREMENT IN INFANCY.

Histidine Requirement in Infancy Nutrition Reviews, Volume 22, Issue 4, April 1964, Pages 114–115, https://doi.org/10.1111/j.1753-4887.1964.tb04853.x Published: 01 April 1964

Optimum histidine requirement of fry African catfish,Clarias gariepinus(Burchell)

Dietary histidine requirement of fry African catfish, Clarias gariepinus (2.57 ± 0.02 cm; 0.22 ± 0.03 g) was quantified by feeding casein–gelatin-based isonitrogenous (40% crude protein) and isocaloric (17.90 kJ g−1 gross energy) amino acid test diets with graded levels of histidine (0.25%, 0.30%, 0.35%, 0.40%, 0.45% and 0.50% dry diet) in eighteen 80 L indoor circular aqua-coloured troughs provided with the flow-through system for 12 weeks. Maximum absolute weight gain (2.66), best feed conversion ratio (1.29), highest protein efficiency ratio (1.94), protein retention efficiency (34%) and energy retention efficiency (70.4%) were achieved at 0.40% dietary histidine. Broken-line and non-linear regression models were adopted to assess dietary histidine requirement for C. gariepinus. When analysed using broken-line regression model these parameters were also best at 0.40% dietary histidine corresponding to 1.0% protein, respectively, whereas using second-degree polynomial regression analysis, histidine requirement was obtained at 0.42%, 0.41%, 0.40%, 0.41% and 0.41% of dry diet, corresponding to 1.05%, 1.02%, 1.0%, 1.02% and 1.02% protein respectively. Based on the broken-line and second-degree polynomial regression analyses of the growth and nutrient retention data, optimum histidine requirement of fry C. gariepinus was found to be in the range of 0.40–0.42% dry diet, corresponding to 1.0–1.05% of dietary protein.

Functional Analysis of a Histidine Auxotrophic Mutation in Gibberella zeae

A plant pathogenic fungus, Gibberella zeae (anamorph: Fusarium graminearum), not only generates economic losses by causing disease on cereal grains, but also leads to severe toxicosis in human and animals through the production of mycotoxins in infected plants. Here, we characterized a histidine auxotrophic mutant of G. zeae, designated Z43R1092, which was generated using a restriction enzyme-mediated integration (REMI) procedure. The mutant exhibited pleiotropic phenotypic changes, including a reduction in mycelial growth and virulence and loss of sexual reproduction. Outcrossing analysis confirmed that the histidine auxotrophy is linked to the insertional vector in Z43R1092. Molecular analysis showed that the histidine requirement of Z43R1092 is caused by a disruption of an open reading frame, designated GzHIS7. The deduced product of GzHIS7 encodes a putative enzyme with an N-terminal glutamine amidotransferase and a C-terminal cyclase domain, similar to the Saccharomyces cerevisiae HIS7 required for histidine biosynthesis. The subsequent gene deletion and complementation analyses confirmed the functions of GzHIS7 in G. zeae. This is the first report of the molecular characterization of histidine auxotrophy in G. zeae, and our results demonstrate that correct histidine biosynthesis is essential for virulence, as well as sexual development, in G. zeae. In addition, our results could provide a G. zeae histidine auxotroph as a recipient strain for genetic transformation using this new selectable marker.

Histidine maintenance requirement and efficiency of its utilization in young pigs

An experiment was conducted in young pigs (initial BW 10.1 kg) to estimate the maintenance requirement for histidine and its efficiency of utilization for protein accretion using a comparative slaughter technique. Three groups of six pigs each were fed a purified diet supplying 0, 14 or 56 mg histidine per kg BW0.75. Following 21 d of feeding, pigs were killed for whole body compositional analysis. A representative group of six pigs was killed at the beginning of the experiment. Retention of histidine and total N were the main criteria of response. Histidine retention (R2 = 0.73) and N retention (R2 = 0.78) were linear functions of histidine intake (p < 0.001). Histidine requirement for zero histidine retention was 15.5 mg/kg BW0.75, whereas histidine required for zero N retention was 4.1 mg/kg BW0.75. At zero histidine retention, the pigs retained daily 82 mg N/kg BW0.75, presumably due to the degradation of histidine-rich compounds such as haemoglobin and/or carnosine. The slope of the regression line relating histidine retention to N retention indicated that 105 mg of histidine was deposited per gram of total N which was considerably less than the estimated histidine concentration in body protein (179 mg/g N). Based on the slopes of regression equations for histidine and N retention, marginal efficiency of histidine utilization was calculated to be 0.94 and 1.34, respectively.

Dietary histidine requirement of fingerling Indian major carp, Cirrhinus mrigala (Hamilton)

An 8-week growth trial was conducted to determine the dietary histidine requirement of the Indian major carp, Cirrhinus mrigala fingerling (length 4.22 ± 0.45 cm; weight 0.61 ± 0.08 g; n = 40). Isonitrogenous (400 g kg−1 crude protein) and isoenergetic (17.90 kJ g−1 gross energy) diets with graded levels of l-histidine (2.5, 5.0, 7.5, 10.0, 12.5 and 15.0 g kg−1 dry diet) were formulated using casein and gelatin as a source of intact protein, supplemented with l-crystalline amino acids. Twenty fish were randomly stocked in 70-L indoor polyvinyl circular fish tank (water volume 55-L, water exchange rate 1–1.5 L min−1) and fed experimental diets at the rate of 5% of their body weight/day divided over two feedings at 08:00 and 16:00 h. Maximum live weight gain (295%), best feed conversion ratio (FCR) (1.48) and protein efficiency ratio (PER) (1.69) occurred at 7.5 g kg−1 of dietary histidine level. When live weight gain, FCR and PER data were analysed using second-degree polynomial regression, the break points indicated histidine requirements at 9.4, 8.6 and 8.5 g kg−1 of dry diet respectively. Significantly (P < 0.05) higher whole body protein and low moisture values were recorded at 7.5 g kg−1 histidine level. Body fat increased significantly (P < 0.05) with increasing histidine levels. However, at 7.5 and 10 g kg−1 histidine diets body fat did not differ (P > 0.05) to each other. Ash content of fish fed diets containing various levels of histidine did not differ except at 2.5 and 5.0 g kg−1 inclusion levels where significantly (P < 0.05) higher ash was recorded. Protein deposition was also found to be significantly (P < 0.05) higher in the 7.5 g kg−1 histidine diet. Based on the polynomial regression analysis of FCR and PER data, it is recommended that the diet for fingerling C. mrigala should contain histidine at 8.5 g kg−1 of dry diet, corresponding to 21.25 g kg−1 of dietary protein for optimum growth and efficient utilization of feed.

Revisiting Purine-Histidine Cross-Pathway Regulation in Saccharomyces cerevisiae

Because some metabolic intermediates are involved in more than one pathway, crosstalk between pathways is crucial to maintaining homeostasis. AMP and histidine biosynthesis pathways are coregulated at the transcriptional level in response to adenine availability. 5'-Phosphoribosyl-4-carboxamide-5-aminoimidazole (AICAR), a metabolic intermediate at the crossroads between these two pathways, is shown here to be critical for activation of the transcriptional response in the absence of adenine. In this study, we show that both AMP and histidine pathways significantly contribute to AICAR synthesis. Furthermore, we show that upregulation of the histidine pathway clearly interferes with regulation of the AMP pathway, thus providing an explanation for the regulatory crosstalk between these pathways. Finally, we revisit the histidine auxotrophy of ade3 or ade16 ade17 mutants. Interestingly, overexpression of PMU1, encoding a potential phosphomutase, partially suppresses the histidine requirement of an ade3 ade16 ade17 triple mutant, most probably by reducing the level of AICAR in this mutant. Together our data clearly establish that AICAR is not just a metabolic intermediate but also acts as a true regulatory molecule.

Dietary Histidine Requirement Of Fingerling Indian Major Carp, Labeo Rohita (Hamilton)

A 6-week growth trial was conducted to assess the dietary histidine requirement of fingerling Indian major carp, Labeo rohita (3.50±0.04 cm; 0.40±0.02 g) by using amino acid test diets (40% crude protein; 4.28 kcal/g) containing casein, gelatin, and L-crystalline amino acids. Diets with graded levels of histidine (0.25, 0.50, 0.75, 1.00, 1.25, and 1.50% of the diet) were fed to tripli- cate groups of fingerlings at 5% of their body weight divided into two feedings (07:00 and 17:30). Live weight gain, specific growth rate, protein efficiency ratio, and feed conversion ratio were sig- nificantly (p&lt;0.05) affected by dietary histidine concentration. Weight gain and conversion effi- ciencies were best at 0.75% dietary histidine. Whole body protein content was highest and mois- ture and fat were lowest in the 0.75% dietary histidine treatment while whole body ash was the same at all treatment levels. Second-degree polynomial regression analysis of the live weight gain and feed conversion ratio resulted in more accurate histidine requirement estimates of 0.90 and 0.82% of the dry diet, respectively, corresponding to 2.25 and 2.05% of the dietary protein. It is recommended that dietary histidine be included at a level of 0.82% of the feed, correspond- ing to 2.05% of the dietary protein, for optimal growth in L. rohita fingerlings.

Optimum Ratio of Histidine in the Piglet Ideal Protein Model and its Effects on the Body Metabolism

Two growth trails were conducted to determine the optimum ration of histidine in 10-20kg piglet ideal protein model. Four diets containing 0.23%, 0.31%, 0.39% and 0.47% digestible histidine (0, 0.08%, 0.16%, 0.24% crystalline histidine supplemented into the basal diet) were fed to 96 piglets of mean initial body weight 10.3 ± 1.08kg for 18d in Experiment 1. Average daily gain, average daily feed intake and feed conversion efficiency were inhibited (P < 0.05) with the diet containing 0.23% digestible histidine. Performance was maximized with 0.31% digestible histidine. As the dietary histidine increased, blood urea nitrogen and serum cholesterol concentration were influenced significantly. The concentrations of serum histamine and free histidine did not change with increase in digestible histidine from 0.23 to 0.31%, but higher supplementation resulted in a significant linear increase in both serum parameters. It was concluded that the dietary level of 0.23% digestible histidine does not meet the requirement of 10-20kg piglets. Based on the results from Experiment 1, Experiment 2 was designed to determine the optimum ratio of lysine:histidine in the ideal protein model of 10-20kg piglet. Ninety-six Large White ‐ Landrace piglets weighing 10.2 ± 0.88kg were divided into 4 groups. They were fed four diets containing 0.26, 0.29, 0.32 or 0.35% digestible histidine, formulated by adding 0.03, 0.06, 0.09 or 0.12% crystalline histidine to the basal diet. The trial lasted for 21 days. Results showed that performance was significantly improved with 0.32 and 0.35% digestible histidine. As dietary histidine increased, blood urea nitrogen tended to decrease but not significant at P < 0.05. Serum cholesterol concentration increased with an increase in dietary histidine level and reached a maximum at 0.35%. Serum histamine increased with increasing dietary histidine. Free serum histidine increased linearly with increased dietary histidine. From both experiments it was concluded that the digestible histidine requirement for 10-20kg piglets was 0.31% and that the optimum ratio of dietary lysine to histidine should be 100:30. The concentrations of cholesterol, histamine and free histidine in serum were sensitive parameters to measure changes in dietary histidine levels.