The determination of nutritional requirements in rats: mathematical modeling of sigmoidal, inhibited nutrient-response curves

DHA from microalgae Schizochytrium spp. (Thraustochytriaceae) modifies the inflammatory response and gonadal lipid profile in domestic cats

The present study aimed to evaluate the inflammatory response, oxidative status and fatty acid deposition in reproductive tissues of cats supplemented with the dried microalgae Schizochytrium spp. (Thraustochytriaceae) as a DHA source. Thirty-seven cats (males, n 21; females, n 16; 11·5 (sd 0·5) months of age) were divided by sex into five groups. Treatment diets contained algae biomass at 4·0, 8·0, 12·0 or 16·0 g/kg replacing poultry fat (n-6 source). Cats were fed the respective diet for 62 d and neutered on day 58. Blood samples were collected at the beginning of the experiment (day 1), before neutering (day 58) and 4 d after surgery (day 62) for analysis of inflammation and oxidative markers. Acute-phase protein levels were altered (P < 0·01) in the postoperative period, without any treatment effect (P > 0·05). PGE2 concentrations after surgery were reduced linearly (R2 0·8706; P = 0·002) with microalgal inclusion. Blood platelet count was reduced (P = 0·001) after the surgery regardless treatment, but it was higher in the DHA group compared with control (P < 0·001). The DHA deposition (testicles, R2 0·846; ovaries, R2 0·869) and the n-6:n-3 ratio (testicles, R2 0·859; ovaries, R2 0·955) in gonads had a pattern which fitted a quadratic model. DHA from Schizochytrium spp. modifies PGE2 response after the surgery in cats. The physiological roles of the DHA in the reproduction of cats were not investigated, but its gonadal deposition after supplementation was observed.

Weight gain responses of laying-type pullets to methionine plus cystine intake

Each individual in the population has a distinct maximum growth potential, and the growth curve may vary depending on the response to nutrient intake, growth phase and variability among animals. The present study aimed to (1) model weight gain (WG) response to methionine+cystine (Met+Cys) supply using different mathematical functions, (2) identify functions that better fit the growth responses of pullets, (3) determine the Met+Cys requirements that maximize WG based on breeding standards and (4) partition the Met+Cys requirements for WG and maintenance. Three trials were performed using 1448 laying-type pullets. We adopted a completely randomized design with eight treatments and six replicates. The first trial (2 to 6 weeks, P1) used 15 pullets per experimental unit. The second and third trials (8 to 12 weeks, P2; 14 to 18 weeks, P3) were used eight pullets per replicate. The Met+Cys levels were obtained using a dilution technique. The mathematical functions used to describe WG responses to Met+Cys intake were broken line, broken line with curvilinear ascendancy, Michaelis-Menten, saturation kinetics and three logistic and three exponential models. Models were selected using the Bayesian information criterion and evaluated by residual analysis. It was possible to model the responses using the studied functions. The best functions were obtained by logistic and sigmoidal models in P1 and P2, and with the broken line by the curvilinear ascendancy model in P3. The Met+Cys intake that determined the maximum potential for WG (WGmax) in P1, P2 and P3 were 313, 381 and 318 mg/day, respectively. The Met+Cys requirements for WG were 20, 22 and 27 mg/g, and for maintenance were 214, 53 and 30 mg/kgBW0.75 for P1, P2 and P3, respectively.

Relative Bioavailability of Niacin Supplements for Dairy Cows: Effects of Rumen Protection and of Feed Processing

The present study aimed to examine the effective systemic bioavailability of niacin- with particular focus on its galenic form-and feed processing. Experiment 1 was conducted with 35 dairy cows to investigate the effects of various doses of oral supplemented nicotinic acid (NA) either in differing galenic forms (non-rumen protected (nRP) vs. rumen protected form (RP)) on serum niacin concentrations. Experiment 2 was designed as a pharmacokinetic study examining the serum niacin kinetics over 24 h after giving a single oral bolus of 24 g nRP or RP NA admixed in either pelleted or ground concentrate. In both experiments, only the niacin vitamer nicotinamide (NAM) was detected. Results of experiment 1 showed that both galenic forms at a dose of 24 g/cow daily elevated NAM concentrations at the beginning of the experiment. Despite a daily supplementation, NAM concentrations decreased continuously towards the end of the experiment which was more steeply in nRP NA (p = 0.03). On experimental day 21, NAM concentrations were higher when feeding RP NA (p = 0.03) and the highest dose (24 g/day and cow) (p < 0.01). Results of experiment 2 indicated that nRP and RP were characterized by similar pharmacokinetic profiles resulting in similar areas under the curves as a net result of the kinetic counterbalancing alterations. Pelleting seemed not to influence the relative bioavailability.

Estimation of the tryptophan requirement in piglets by meta-analysis

There is no consensus concerning the Trp requirement for piglets expressed relative to Lys on a standardized ileal digestible basis (SID Trp : Lys). A meta-analysis was performed to estimate the SID Trp : Lys ratio that maximizes performance of weaned piglets between 7 and 25 kg of BW. A database comprising 130 experiments on the Trp requirement in piglets was established. The nutritional values of the diets were calculated from the composition of feed ingredients. Among all experiments, 37 experiments were selected to be used in the meta-analysis because they were designed to express the Trp requirement relative to Lys (e.g. Lys was the second-limiting amino acid in the diet) while testing at least three levels of Trp. The linear-plateau (LP), curvilinear-plateau (CLP) and asymptotic (ASY) models were tested to estimate the SID Trp : Lys requirement using average daily gain (ADG), average daily feed intake (ADFI) and gain-to-feed ratio (G : F) as response criteria. A multiplicative trial effect was included in the models on the plateau value, assuming that the experimental conditions affected only this parameter and not the requirement or the shape of the response to Trp. Model choice appeared to have an important impact on the estimated requirement. Using ADG and ADFI as response criteria, the SID Trp : Lys requirement was estimated at 17% with the LP model, at 22% with the CLP model and at 26% with the ASY model. Requirement estimates were slightly lower when G : F was used as response criterion. The Trp requirement was not affected by the composition of the diet (corn v. a mixture of cereals). The CLP model appeared to be the best-adapted model to describe the response curve of a population. This model predicted that increasing the SID Trp : Lys ratio from 17% to 22% resulted in an increase in ADG by 8%.

Protein level affects the relative lysine requirement of growing rainbow trout (Oncorhynchus mykiss) fry

The effect of two digestible protein levels (310 and 469 g/kg DM) on the relative lysine (Lys; g Lys/kg DM or g Lys/100 g protein) and the absolute Lys (g Lys intake/kg0·75 per d) requirements was studied in rainbow trout fry using a dose–response trial. At each protein level, sixteen isoenergetic (22–23 MJ digestible energy/kg DM) diets were tested, involving a full range (2–70 g/kg DM) of sixteen Lys levels. Each diet was given to one group of sixty rainbow trout fry (mean initial body weight 0·78 g) reared at 15°C for 31 feeding d. The Lys requirements were estimated based on the relationships between weight, protein, and Lys gains (g/kg0·75 per d) and Lys concentration (g/kg DM or g/100 g protein) or Lys intake (g/kg0·75 per d), using the broken-line model (BLM) and the non-linear four-parameter saturation kinetics model (SKM-4). Both the model and the response criterion chosen markedly impacted the relative Lys requirement. The relative Lys requirement for Lys gain of rainbow trout estimated with the BLM (and SKM-4 at 90 % of the maximum response) increased from 16·8 (19·6) g/kg DM at a low protein level to 23·4 (24·5) g/kg DM at a high protein level. However, the dietary protein content affected neither the absolute Lys requirement nor the relative Lys requirement expressed as g Lys/100 g protein nor the Lys requirement for maintenance (21 mg Lys/kg0·75 per d).

Kinetics and metabolism of zearalenone in young female pigs

The fate of a single bolus of the Fusarium mycotoxin zearalenone (ZON) given intravenously to pigs was followed up. Pigs were equipped with duodenal re-entrant cannulas, post-valvular T-shape cannulas and with a urinary bladder balloon catheter. The animals were divided into three groups. Pigs of the control group were injected with ZON (Co), and pigs of the second group were also injected with ZON but their duodenal digesta was quantitatively exchanged for 12 h with corresponding pigs of the third group, not injected with ZON. Therefore, the second group had a disrupted entero-hepatic cycling of ZON (DEHC) and the third one had an induced entero-hepatic cycling of ZON (IEHC). The kinetic profile of ZON and its metabolites in plasma and their flow with urine, duodenal and ileal digesta and with faeces was examined over the next 72 h after the bolus was given. Eleven days later, pigs were slaughtered for collection of bile, urine and liver to analyse ZON residues. In all specimens examined, alpha-zearalenol (ZOL) was detected as the only metabolite of ZON. Kinetic evaluation of the plasma data revealed that the terminal elimination half-life of ZON was reduced from 2.63 h in pigs of Co-group to 1.1 h when EHC of ZON was disrupted for 12 h (DEHC-group). The maximum ZON concentration in plasma of pigs with the IEHC was found at 2.73 h after the bolus was given to their counterparts. The percentage of the alpha-ZOL- and ZON-area under the curves (AUC) estimated for the IEHC-group amounted to approximately 18% of the corresponding AUC of the Co-group which would suggest that a substantial proportion of both substances are re-cycled via entero-hepatic re-circulation. Cumulative recovery of ZON and alpha-ZOL, expressed as percentage of the ZON-bolus was characterized by a saturation kinetics in urine and duodenal digesta, and after 72 h, the respective values for Co-, DEH-, and IEHC-groups were 70%, 55% and 12%; and 35%, 22% and 11%. Faecal excretion started to increase steeply after 48 h and still continued to increase after 72 h when the cumulative excretion was 6%, 3% and 2% for Co-, DEHC- and IEHC-groups respectively. Fourteen days after the bolus injection, ZON and alpha-ZOL concentrations in bile, liver and urine were lower than the detection limits of the applied method. The results would suggest that within this period of time a massive single bolus of ZON is nearly completely eliminated from the body.

Partition of Nitrogen Excretion in Urine and the Feces of Holstein Replacement Heifers

Increasing public concern has been focused on animal production systems as a major nonpoint source of pollution. These studies were conducted to further our understanding of whole-animal N metabolism, N excretion, and its partition between feces and urine in growing dairy heifers. Isocaloric diets [2.31 Mcal of metabolizable energy (ME)/kg of dry matter (DM)], ranging from 12.4 to 34.2 g of N/kg of DM, were fed to Holstein heifers in 2 experiments at approximately 1.8 times maintenance. Diets were formulated to provide 54 to 143% of the ruminal ammonia requirements as predicted by the Cornell Net Carbohydrate and Protein System. Increasing the N content of the diet increased urinary N excretion and N balance, but did not affect fecal N excretion. Holstein heifers fed low N diets were able to maintain growth rates consistent with current recommendations while at the same time reducing N excretion, in particular nitrogenous compounds that are readily converted to ammonia. However, more research is needed before this type of diet is recommended for growing heifers because of possible changes in body composition that may affect future milk production and performance.

Meta-analysis of nitrogen balance studies for estimating protein requirements in healthy adults

BACKGROUND

The most recent international dietary protein recommendations for healthy adults are those developed and proposed by the 1985 FAO/WHO/UNU Joint Expert Consultation.

OBJECTIVE

The objective was to analyze available nitrogen balance data to establish new recommendations for the protein required by healthy adults.

DESIGN

Data were gathered from published nitrogen balance studies that had as their primary objective either the estimation of basal or maintenance requirements or the testing of the adequacy of specific nitrogen intakes in healthy adults. These data were synthesized to characterize the distribution of individual protein requirements; the effects of climate of the study site, adult age, sex, and dietary protein source on individual requirements; and the midpoint of and the variability between the protein requirements of healthy persons.

RESULTS

Data for 235 individual subjects, each studied at >or= 3 test protein intakes, were gathered from 19 studies. The median estimated average requirement (EAR) of nitrogen from these data was 105 mg N x kg(-1) x d(-1). Individual requirements were found to fit a log-normal distribution. The median EAR was estimated as the median of this distribution, 105 mg N x kg(-1) x d(-1), whereas the 97.5th percentile (the recommended dietary allowance; RDA) was estimated from the distribution of the log of the requirement (after correction of the total observed variability to remove within-individual variability) as 132 mg N x kg(-1) x d(-1). No significant differences between the climate of the study site, adult age class, sex, or source of dietary protein were observed, although there was an indication that women might have a lower requirement than do men.

CONCLUSION

This meta-analysis provides new recommendations for dietary reference values, ie, an EAR (median) and RDA (97.5th percentile) for healthy adults of 105 and 132 mg N x kg(-1) x d(-1) (0.65 and 0.83 g good-quality protein x kg(-1) x d(-1)), respectively.

Studies on requirement and excess of isoleucine in laying hens

Three production trials and one nitrogen balance trial were conducted with Lohmann Brown hens to determine the requirement for and effects of an excess of isoleucine in layers at different ages (24 to 32 and 46 to 54 wk of age). The trials were designed as dose-response studies where isoleucine-deficient basal rations with 11.4 MJ metabolizable energy per kilogram were supplemented with varying amounts of L-isoleucine. In the production trials, dietary isoleucine concentrations ranged from 0.37 to 1.05%. In the three production trials, maximum daily egg mass was achieved at dietary isoleucine concentrations of between 0.39 and 0.75% (25 to 32 wk of age, daily egg mass 53 g), 0.40 and 0.57% (24 to 32 wk of age, daily egg mass 57 g), and 0.40 and 0.81% (46 to 54 wk of age, daily egg mass 56 g). The corresponding ranges of daily isoleucine intakes were 412 to 770 mg, 436 to 624 mg, and 431 to 874 mg. In the nitrogen balance trial, maximum total nitrogen retention was achieved at dietary isoleucine concentrations of between 0.43 and 0.57%. Dietary isoleucine concentrations higher than 0.8% caused a reduction in hen BW. Dietary isoleucine concentrations higher than 1.0% additionally caused a reduction in the daily egg mass. The study thus shows that the margin between requirement and excess of isoleucine is narrow in laying hens.

Hepatic ascorbic acid saturation is the most stringent response criterion for determining the vitamin C requirement of juvenile European sea bass (Dicentrarchus labrax)

Our main objective was to verify whether the dietary ascorbic acid (AA) requirement of juvenile European sea bass (Dicentrarchus labrax) varies as a function of different physiological needs. Practical diets with eight (0, 5, 10, 20, 40, 80, 160, 320 mg AA/kg diet) levels of ascorbic acid polyphosphate were fed to sea bass (mean weight: 0.7 g) for 15 wk. At the beginning and at the end of the feeding trial, tissues were sampled for vitamin C and hydroxyproline (HyPro) analysis. Dose-dependent responses of skin and whole body HyPro concentrations and hepatic AA concentration to dietary vitamin C levels were observed. Skin and whole body HyPro concentrations were low in sea bass fed AA-deficient diet, 217 and 15 nmol/g tissue, respectively. HyPro levels increased with increasing dietary levels, reaching plateaus of 297 and 45 nmol/g tissue in the skin and whole body at dietary vitamin C levels of at least 5 and 31 mg AA/kg. Hepatic AA level increased with increasing dietary levels, reaching a plateau of 474 pmol/g tissue in juveniles fed at least 121 mg of AA/kg. We concluded that hepatic AA saturation is the most stringent response criterion for determination of the vitamin C requirement in juvenile European sea bass.

Estimates of essential amino acid requirements from dose-response studies with rainbow trout and broiler chicken: effect of mathematical model

A total of 37 dose-response experiments with essential amino acids performed with rainbow trout and broiler chicken were re-evaluated with different mathematical approaches: an exponential model, a four-parameter logistic function, the saturation kinetics model and the broken line approach. The different approaches were compared both with regard to the goodness of fit (r2 and sy.x) and with regard to the allowances which were derived regarding the optimal amino acid level in the diet. The experimental design, particularly the chosen range in dietary amino acid concentration was found to be important for the comparison of models. Amongst the non-linear models, the four-parameter logistic function and the saturation kinetics model appeared superior to the exponential approach, when the range in dietary amino acid concentration was very wide and included both a severely deficient basal level and a level that exceeded the needs of the animal by approximately the factor 2. In these cases, allowances derived from individual experiments were considerably different depending on the model. The allowances based on the exponential and the saturation kinetics approach were 27.7 and 20.7 g lysine/kg DM and 8.0 and 6.3 g methionine/kg DM, respectively, for rainbow trout. For other amino acids studied in rainbow trout the difference due to model was less. Consequently, the predicted 'ideal protein' for rainbow trout was considerably different depending on the model used. The maximum deviation found in different experiments with broiler chicken for the exponential vs. the saturation kinetics approach was 13.0 and 9.7 g lysine/kg and 11.4 and 8.2 g sulfur-containing amino acids/kg, respectively. However, the more restricted the range in dietary concentration was, the lesser became the differences between the different non-linear models. No definite recommendation can therefore be extracted regarding the most suitable, generally applicable mathematical model.

Statistical analysis of nitrogen balance data with reference to the lysine requirement in adults

Statistical analysis of nitrogen balance data is an important approach to the estimation of human nutrient requirement. The usual procedure is to regress nitrogen (N) balance on intake and to define the requirement as intake that would produce zero balance. In the actual application of this methodology, there are a number of options, and in the present study we explore the sensitivity of the regression approach to those options. To put this problem into a realistic context, we examine the current controversy over the lysine requirements of healthy adults. From early N balance studies, investigators concluded that the mean requirement was generally less than 10 mg. kg(-1). d(-1), whereas based on recent (13)C-tracer and metabolic studies, we propose a tentative mean requirement of approximately 30 mg. kg(-1). d(-1). Jones et al. (1956) conducted careful N balance studies from which they derived an estimate of lysine requirement of less than about 8 mg. kg(-1). d(-1). We reanalyzed these data with different choices of modes of analysis, mathematical models, and different assumptions concerning the magnitude of miscellaneous N losses. We find that for these data the choice of a specific mathematical model has only a small effect on resultant estimates of requirement, while estimated requirements are very sensitive to amount of unmeasured losses that are assumed and how the model is applied (whether the aggregate data are fitted in one pass to a single model, or the data for each individual subject are fitted to that individual's unique model). Moreover, our reanalysis suggests that the population requirement for lysine is in the range of 17 to 36 mg. kg(-1). d(-1) and strongly supports a lysine requirement value of about 30 mg. kg(-1). d(-1). In general, our results indicate that whenever possible, N balance data should be analyzed using a square root model fitted to individual data and that the median of the individual requirements so derived be used as the estimate of population requirement. Moreover, clearly any statistical analyses of N balance data should include a sensitivity analysis to determine the influence of underlying assumptions. Finally, the finding that these estimates are highly dependent on the assumed amount of N miscellaneous losses recommends that further studies on these losses and of the factors that influence them are essential.

Response of rainbow trout (Oncorhynchus mykiss) to supplements of individual essential amino acids in a semipurified diet, including an estimate of the maintenance requirement for essential amino acids

We studied the effects of increasing dietary concentrations of each of the following amino acids on growth, feed intake, feed conversion ratio and composition of gain in rainbow trout in six dose-response experiments: L-lysine, L-tryptophan, L-histidine, L-valine, L-leucine and L-isoleucine. Semipurified diets containing 20.1 MJ digestible energy/kg dry matter, with wheat gluten and crystalline amino acids as sole sources of amino acids, were fed to rainbow trout [initial mean body weight (BW) 40-51 g, depending on the amino acid studied]. In one series of 24 diets, lysine concentration ranged from 4.5 to 58.0 g/kg dry matter; in five further series of 12 diets each, concentrations ranged from (in g/kg dry matter): tryptophan, 1.3 to 5.6; histidine, 2.6 to 13.5; valine, 6.2 to 34.2; leucine, 10.0 to 42.0 and isoleucine, 5.0 to 15.3. Each diet was fed to a group of 20 fish for 53-64 d, depending on the amino acid studied. Dry matter intake, weight gain, feed conversion ratio, protein concentration of gain and total protein deposition followed exponential response functions. To achieve 95% of the maximum protein deposition, dietary concentrations of 27.7 g lysine, 2.0 g tryptophan, 5.8 g histidine, 15.7 g valine, 13.6 g leucine and 13.7 g isoleucine/kg dry matter were required. Maintenance requirements, estimated from exponential functions for protein deposition, were [in mg/(100 g BW.d)]: lysine, 1.93; tryptophan, 1.05; histidine, 1.07; valine, 2.92; leucine, 8.26 and isoleucine, 0.91. This corresponds to 4% of the requirement for protein deposition for lysine and isoleucine but 32% for leucine, with the other amino acids being intermediate. Therefore, different dietary amino acid requirement patterns were derived from protein deposition data depending on the chosen level of performance.

Minimum thiamin requirement of weanling Sprague-Dawley outbred rats

To determine the minimum thiamin requirement for maximal growth, two trials were conducted using male weanling Sprague-Dawley rats fed graded doses of thiamin from thiamin mononitrate as a component of a chemically defined diet. This diet included 16% amino acids, 72% sucrose and cornstarch and 5% soybean oil. Total weight gain and food intake were recorded over 2- (trial 1) or 3- (trial 2) wk periods. In trial 1, graded levels of thiamin were fed at 0, 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0 mg thiamin/kg diet, and growth rate reached a plateau in rats fed 0.50 mg thiamin/kg. In trial 2, lower doses of thiamin were fed (0, 0.25, 0.50, 0.75, 1.0, 4.0 and 5.0 mg/kg) to determine the minimum requirement for maximal growth. Using broken-line least-squares analysis, weight gain reached a plateau (6.8 g/d) at a thiamin concentration of 0.55 +/- 0.07 mg/kg. No differences (P > 0.05) in weight gain, food intake or gain:food ratio were observed at thiamin levels at or above 0.5 mg/kg, but food intake was substantially lower (P < 0.05) in rats fed 0 and 0.25 mg thiamin/kg (9.9 and 13.4 g/d, respectively) than in rats fed higher doses of thiamin (16.1 g/d). Hepatic transketolase, a measure of enzymatic thiamin status, increased with dietary thiamin in rats fed diets containing 0-5.0 mg/kg thiamin. However, an inflection point occurred at 0.53 mg thiamin/kg, with the slope being eight times greater below than above the inflection point. The data suggest that the thiamin requirement for maximal growth of weanling rats fed a chemically defined diet is approximately 0.55 mg thiamin/kg, which is substantially below the current National Research Council estimated requirement of 3.1 mg thiamin/kg diet.

Alcoholic liver disease may be prevented with adequate nutrients

Alcoholic liver disease is the result of a synergism between ethanol and nutritional factors. Therefore, it follows that the pathogenesis of alcoholic liver disease may be affected by the regulation of the intake of nutrients as well as by the regulation of the intake of ethanol.

Lysine supplementation of cereal foods: a retrospective

During the period 1950-1975, protein and amino acid metabolism and its application to world nutrition problems constituted a major focus of nutrition research. A large part of this research was concerned with the potential benefits to be expected from lysine supplementation of cereal foods, stimulated by the availability, beginning in 1955, of commercial quantities of L-lysine monohydrochloride from industry. Events during this era and lessons learned are reviewed by the author, a participant in the commercialization of lysine.