True Amino Acid Digestibility Research Articles

Ileal amino acid digestibility assay for the growing meat chicken--comparison of ileal and excreta amino acid digestibility in the chicken

1. The apparent and true amino acid digestibilities in sorghum, wheat, soyabean meal, meat-and-bone meal, fish meal and blood meal for growing meat chickens were determined using an assay based on the collection of digesta from the terminal ileum and comparison was made with digestibility values determined using an excreta-based assay. 2. Five-week-old meat chickens were given maize-soyabean meal basal diet or mixtures of the basal diet and test diets containing the 6 ingredients as the sole source of dietary protein (50:50 on weight basis). Apparent amino acid digestibility values of assay diets at ileal and excreta levels were calculated using chromic oxide as the indigestible marker. True digestibility values were calculated using endogenous outputs determined by feeding a protein-free diet. Amino acid digestibilities of the ingredients were calculated by difference. 3. The site of measurement had no influence on endogenous amino acid output, the exceptions being aspartic acid and glutamic acid. The output of these two amino acids was higher in the excreta. 4. Significant differences were found between ileal and excreta-based digestibility of certain amino acids in some ingredients, with excreta values being usually higher than the ileal values, indicating a net catabolism of amino acids in the large intestine. The degree of net amino acid disappearance was found to be variable among amino acids and ingredients. In general, threonine had the lowest digestibility at the ileal level and, compared with other amino acids, the highest degredation during passage through the hindgut. 5. The results showed that digestibility determination based on excreta collection will overestimate the uptake for some amino acids in some feeds. The degree of overestimation was often considerable, ranging from 8.9% (apparent digestibility of threonine in soyabean meal) to 56% (apparent digestibility of aspartic acid in wheat). It is concluded that digestibility values measured at the terminal ileum provide a more reliable measure of amino acid availability than those measured in the excreta.

Nutritional value of a highly digestible sorghum cultivar for meat-type chickens.

The nutritional value of a newly discovered sorghum mutant cultivar (P851171), with high in vitro protein digestibility, was compared to those of corn and two normal sorghums (P721N and 611Y) in two chick feeding trials. Although 8-20 day protein efficiency ratios and net protein ratios of all three sorghums were inferior to those of corn, P851171 and 611Y had markedly greater mean true amino acid digestibilities (TAAD) than either corn or P721N. In a subsequent 42-day experiment, all three sorghums supported weight gains equal to those of the corn-fed chicks. Feeding suboptimal levels of dietary protein resulted in reduced weight gains and no observed benefits of P851171 or 611Y. Furthermore, chicks fed P851171 exhibited poorer feed/gain values as compared to those fed the other cereals. It is possible that the starch content/carbohydrate profile of P851171 was inferior to that of the other sorghums, which offset its superior TAAD and resulted in poorer broiler performance.

Aminoácidos digestíveis verdadeiros da soja e subprodutos, determinados com galos cecectomizados

Os coeficientes de digestibilidade e o conteúdo de aminoácidos digestíveis verdadeiros da soja e subprodutos foram determinados, utilizando-se galos cecectomizados, onde cada um dos 8 alimentos testados (amostras de soja e subprodutos) foram fornecidos a seis galos (15 g pela manhã e 15 g à tarde, após jejum de 24 horas) e seis galos foram mantidos em jejum, para determinação das perdas endógenas e metabólicas. Após obtidos os coeficientes de digestibilidade e calculados os aminoácidos digestíveis, ajustou-se equações para predizer a composição da soja e seus subprodutos em lisina (LIS), metionina (MET), metionina + cistina (M+C), treonina (TRE) e arginina (ARG), totais e digestíveis, em função da composição em proteína bruta (PB), fibra bruta (FB), extrato etéreo (EE) e matéria mineral (MM). Os coeficientes médios de digestibilidade dos aminoácidos (essenciais e não essenciais, respectivamente) dos farelos de soja 1, 2, 3, 4 e texturizado, sojas integral Jet Sploder, integral tostada e micronizada foram 92,78 e 90,76; 92,66 e 89,70; 93,75 e 91,26; 93,32 e 90,12; 91,55 e 89,08; 94,80 e 92,34; 94,61 e 91,47; 93,20 e 90,47 %. As equações foram bem ajustadas, cujos valores de R² foram superiores a 91% e a PB apresentou alta correlação positiva, onde as equações LIS = -0,32161 + 0,06731PB (R² = 0,99); MET = 0,02263 + 0,01323PB (R² = 0,96); M+C = 0,078949 + 0,02563PB (R² = 0,94); TRE = 0,20930 + 0,03533PB (R² = 0,95); ARG = -0,39589 + 0,08022PB (R² = 0,98) e LIS = -0,29472 + 0,06319PB (R² = 0,98); MET = 0,02884 + 0,01228PB (R² = 0,93); M+C = 0,08974 + 0,0222PB (R² = 0,91); TRE = 0,15813 + 0,03235PB (R² = 0,95) e ARG = -0,32129 + 0,07681PB (R² = 0,96), podem predizer o conteúdo em aminoácidos totais e digestíveis da soja e subprodutos, respectivamente.

Effects of Casein and Protein-free Diets on Endogenous Amino Acid Losses in Pigs

Quantification of endogenous amino acid loss at the terminal ileum is an essential means for calculation of the true amino acid digestibility of a feedstuff. Since nitrogen appeared in the determined diet or not could shift the results very much, also, none of digestibility markers could be recovered with 100% rate at the terminal ileum, the objectives of the present study were: (1) to determine endogenous amino acid losses when fed either a casein diet or a protein-free diet and (2) to examine the reliability of chromic oxide or acid insoluble ash in the protein-free diet. Six ileal-cannulated pigs (65′1.85 kg BW) with a simple T-cannula in the terminal ileum were used in a replicated 3x3 Latin square designed trial, after allowed a 14 d recuperation period. Each test period ran for 12 days comprised of a 10 d adjustment period and a 2 d collection period. The endogenous AA losses of His, Ile, Lys, Cys, Thr, Val, Trp, Asp, Glu, and Ser from pigs fed the casein diet were significantly higher than those of the protein-free diet (p 0.05). These data suggest that endogenous amino acid loss could be underestimated when a protein-free diet is used. A direct effect of dietary peptides on the endogenous amino acid loss was found when the casein diet was fed. Our results also indicate that acid insoluble ash can be used as an inert marker as an alternative to chromic oxide when measuring endogenous amino acid loss.

Additivity and Associative Effects of Metabolizable Energy and Amino Acid Digestibility in Barley and Canola Meal for White Pekin Ducks

An experiment was conducted using the TMEn bioassay method to investigate the additivity and associative effects of metabolizable energy and amino acid digestibility in barley and canola meal for White Pekin ducks. Additivity was tested by comparing the difference between observed values determined in a complete diet and predicted values from measurements determined with individual ingredients (barley and canola meal). Six ducks each were assigned to diets of barley, canola meal, the complete diet, and dextrose. Dextrose-fed ducks were used for estimation of endogenous losses for calculation of true amino acid digestibility. The observed AME, TME, AMEn, and TMEn values in the complete diet were 0.065, 0.083, 0.016, and 0.023 (kcal/g), respectively, numerically higher than predicted values. Differences between observed and predicted values were not significant (P > 0.05), indicating that the AME, AMEn, TME, and TMEn in barley and canola meal were all additive. In general, observed values for apparent amino acid digestibility (AAAD) and true amino acid digestibility (TAAD) in the complete diet were higher than those predicted from individual ingredients. Observed AAAD for lysine, histidine, tryptophan, alanine, and aspartate were higher (P < 0.05) than predicted values, indicating that digestibilities of these amino acids were not additive. The mean of AAAD in canola meal (77.29%) was higher (P < 0.05) than the observed values of barley (52.2%) and complete diet (64.55%). For TAAD values, differences between observed and predicted values were significant for lysine, histidine, and tryptophan (P < 0.05). The mean of TAAD in canola meal, barley, and complete diet were 85.88, 80.87, and 81.33%, respectively. The average difference between observed and predicted values for TAAD (1.18 %) was smaller than that of AAAD (5.41%). These results indicated that ME values for barley and canola meal were additive in the complete diet but that digestibilities of some amino acids were not additive; they further suggested that there were some associative effects of amino acids in barley and canola meal for ducks.

Effect of Ash Content on Protein Quality of Meat and Bone Meal

The effect of ash concentration on amino acid (AA) composition, true AA digestibility, and protein efficiency ratio (PER; weight gain per unit of protein intake) of meat and bone meal (MBM) was evaluated. Commercially rendered MBM samples containing 16 to 44% ash were obtained from two sources. Additional samples of MBM varying in ash from 9 to 63% were obtained by chloroform floatation or lab screening of a beef crax sample. Protein quality of selected MBM samples was assessed by determining true AA digestibility using the precision-fed cecectomized rooster assay and by a PER chick growth assay wherein chicks were fed 10% CP diets containing a MBM as the only source of dietary protein from 8 to 18 d of age. Increases in Ala, Pro, Gly, and Arg as a percentage of CP were observed in all MBM samples as ash percentage increased, with Pro and Gly accounting for most of the increase. In contrast, the levels (% of CP) of all essential AA, other than Arg, decreased as ash level increased. For example, Lys concentrations per unit of CP decreased from 5.7 to 4.0% as ash increased from 9 to 63%. There was little or no effect of ash content on AA digestibility of MBM varying in ash from 9 to 44%. The PER of MBM markedly decreased from 3.34 to 0.72 as ash increased from 16 to 44%, and most of the effects of ash on PER were not due to differences in dietary Ca and P levels. The results indicate that the reduction in protein quality of MBM as ash content increases is almost entirely due to a decrease in analyzed essential AA per unit of CP, not a decrease in digestibility of AA.

Prediction of the standardized ileal true digestibility of amino acids from the chemical composition of oilseed meals in the growing pig

Digestibility experiments using growing pigs fitted with an ileorectal anastomosis were performed to measure the standardized ileal true digestibility (ITD) of amino acids in five cotton seed meals (CSM) and three palm kernel meals (PKM), differing in their level of non starch polysaccharides (NSP), as expressed by NDF content and the nitrogen content of NDF (N NDF). The NDF content in CSM ranged from 273 to 475 g kg −1 on dry matter (DM) and the crude protein content from 384 to 506 g kg −1 DM. The latter values were not correlated with the NDF content. For PKM, NDF varied from 592 to 686 g kg −1 and the crude protein content from 151 to 177 g kg −1. Results obtained for CSM clearly demonstrate a curvilinear relationship, except for methionine, between ITD of amino acids and NDF content. Furthermore, if the composition of the CSM as ash, fat, total nitrogen, nitrogen from NDF (N NDF) and total gossypol (TGOS) contents is known (g kg −1 DM), the quantity of digestible amino acid can be predicted for lysine, threonine and tryptophan with reasonable precision, but less for sulfur amino acids. As an example for lysine, dLys ( g kg −1 DM)=6.5116(1.0939)+0.1411 N(0.0158)−0.1673 NNDF(0.0091)−0.0124 NDF (0.0010) R 2=0.993. For PKM, the relationships were more difficult to assess because of a narrow range in NDF level and the heterogeneity of response between pigs, especially for the higher NDF contents. In addition, the current data confirmed that the nitrogen content in the NDF fraction of NSP, often considered in ruminant protein nutrition, could be also an useful predictor of true ileal digestible values for selected amino acids in the pig,

Uso de rações à base de aminoácidos digestíveis para poedeiras

O objetivo deste experimento foi comparar o desempenho de poedeiras alimentadas com rações formuladas com diferentes níveis de lisina e aminoácidos sulfurosos digestíveis. Um total de 144 poedeiras leves, com 24 semanas de idade, foi distribuído ao acaso em três tratamentos com oito repetições de seis aves. Uma ração de alta digestibilidade em aminoácidos (AD) à base de milho e farelo de soja, como controle positivo, foi comparada a outras rações contendo alimentos alternativos em substituição parcial do milho e do farelo de soja. A segunda ração foi formulada com baixa digestibilidade (BD) de lisina e aminoácidos sulfurosos em relação à ração AD. A terceira ração (BD+AA) foi similar à ração BD, mas suplementada com L-Lisina·HCL e DL-Metionina, adicionadas para se obterem níveis de aminoácidos digestíveis iguais à ração AD. As avaliações foram realizadas em três períodos de 28 dias. Não houve efeito das rações sobre consumo de ração, produção, peso e massa de ovos e conversão alimentar por massa de ovo. A qualidade interna do ovo medida pela unidade Haugh e pelos índices de gema e de albúmen também não foi afetada. Os resultados do presente trabalho não confirmaram os benefícios de se formularem rações com base em aminoácidos digestíveis para poedeiras, a partir da informação de aminoácidos digestíveis obtida com galos cecectomizados.

Protein and energy evaluation of soybean meals processed from genetically modified high-protein soybeans

A conventional and two genetically modified soybean samples were processed to dehulled soybean meal (SBM) at a pilot plant and were compared with SBM from a commercial processing plant. Crude protein levels (%) of the experimental SBM samples were M700, 52.5; M702, 53.4; and M703, 62.7. The commercial SBM sample (UI) contained 47.5% protein. Amino acid, gross energy, lipid, and fiber analyses were carried out, and true metabolizable energy and true amino acid digestibility were determined with adult cecectomized cockerels. Digestible Lys, Met, Cys, Thr, and Val, and also TMEn, were higher (P < 0.05) and NDF, fat, and phospholipids were lower in M703 than in the other SBM samples. The results of this study indicate that M703 has considerable advantages over conventional SBM as a feed ingredient for broiler chickens.

Ileal true digestibility of amino acids in wheat milling by-products for pigs

Ten batches of wheat milling by-products - 3 of wheat middlings (WM), 4 of wheat feed (WF), 3 of wheat bran (WB) - were analysed and studied for their protein and amino acid ileal true digestibility (ITD). Each batch was tested on four castrated male pigs weighing between 35 and 95 kg, and fitted with an end-to-end ileo-rectal anastomosis. In all types of by-products, lysine and threonine were among the least digestible amino acids, whereas methionine was among the most digestible ones. N and all amino acids ITD decreased significantly ( P < 0.05) from WM to WF and to WB. In WM, the average N, lysine, threonine and methionine ITD values were 93.6, 90.8, 90.4 and 95.1%, respectively. They decreased to 85.5, 86.6, 83.3 and 91.5%, respectively in WF and down to 70.1, 68.3, 68.4 and 78.9%, respectively in WB. N and all amino acids ITD was predicted according to either the ratio of the feedstuff fibre to amino acid concentrations, or the proportion of total N bound to the NDF (neutral detergent fibre) residue, or both. For most amino acids, the use of CF (crude fibre), ADF (acid detergent fibre) or ADL (acid detergent lignin) as fibre criteria provided accurate equations with coefficient of determination higher than 90%.

A comparison of total and digestible amino acids in diets for broilers and layers

Eleven samples of food ingredients were analysed for their total and true digestible amino acid content, apparent metabolisable energy and other components. Large batches of these ingredients were retained for a broiler and a layer experiment. Four layer diets were formulated at 0.97 and 0.90 of total and digestible amino acid requirements for egg production using the analysed ingredients. Eight broiler diets were also formulated from 1.0 to 0.91 of total and digestible amino acid requirements in starter and finisher diets. Proximate and amino acid analyses and AME values were within the normal range for the 11 foodstuffs. Digestibility of amino acids was high with very few exceptions, e.g. cottonseed meal, meat and bone meal. Diets formulated on a total or digestible amino acid basis gave no differences in egg production parameters or broiler production parameters with no effect of level of inclusion. However, the main effects showed that diets formulated on a total compared to a digestible amino acid basis gave better growth rate and feed conversion efficiency in broilers. It was concluded that nutrient specifications for layers and broilers are not sufficiently precise to be able to differentiate between 1.97 and 0.90 of requirement for egg production or 1.0 and 0.91 for broiler growth. The use of digestible amino acids may be justified in diet formulations only when unusual protein concentrates with low amino acid digestibility values are used in large amounts.

The influence of cecectomy on metabolizable energy and amino acid digestibility of select feedstuffs for white Pekin ducks

Twenty-four cecectomized and 24 intact White Pekin ducks were used in two experiments to assess the influence of cecectomy on ME and amino acid digestibility of several feed ingredients for ducks. Corn and soybean meal (SBM) were evaluated in Experiment 1, and bakery meal (BM), red dog (RD), and wheat middlings (WM) were evaluated in Experiment 2. Nitrogen-corrected true metabolizable energy and amino acid digestibility of the ingredients were assayed concurrently. In Experiment 1, TME of corn was higher (P < or = 0.05) in cecectomized ducks, and intact ducks demonstrated greater (P < or = 0.05) ability to utilize the energy in SBM. Intact ducks exhibited higher (P < or = 0.05) true digestibilities of lysine and methionine. True digestibility of tryptophan was higher (P < or = 0.05) for cecectomized ducks. True digestibility of indispensable amino acids in SBM did not differ (P > or = 0.05) between cecectomized and intact ducks. In Experiment 2, cecectomized ducks exhibited greater (P < or = 0.05) ability to utilize the energy in RD. Intact ducks exhibited greater (P < or = 0.05) ability to utilize the energy in WM. True digestibility of indispensable amino acids in BM, RD, and WM was variable. Results of the present study suggest that the effect of cecectomy on nutrient digestibility in ducks is dependent on the feedstuff assayed.

Nutritive value for broilers of meals derived from newly developed varieties of yellow-seeded canola

This study was conducted to determine the nutritive value of the meals derived from recently developed lines/varieties of canola. The samples included the yellow-seeded Brassica napus, B. juncea and B. rapa and the brown-seeded B. napus canola. Two commercial meals from yellow-seeded B. rapa and brown-seeded B. napus canola served as control samples. All samples were of canola quality and contained between 11.4 and 21.7 μmol g −1 of glucosinolate in the oil free meal. The evaluation involved chemical analyses of protein, amino acids, carbohydrates, dietary fibre, ash and ether extract, in vitro protein digestibility and true availability of energy (TME n) and amino acids. The overall feeding quality was evaluated in a 2-week growth trial with 4-day-old broiler chickens. There were no major differences among the meals with regard to amino acid content when expressed in g per 16 g N. The levels of amino acids reflected quantitative differences in the content of protein which for yellow-seeded B. napus and B. juncea and brown-seeded B. napus canola approached or exceeded 460 g kg −1 DM. Dietary fibre content varied from 271 to 352 g kg − 1 DM with the lowest value representing the yellow-seeded B. napus and the highest the commercial meal from brown-seeded B. napus canola. In vitro protein digestibility values showed minor differences among the samples. True digestibility of amino acids averaged 84.1% with only minor differences among the samples. True metabolizable energy content was highest in the yellow-seeded B. napus sample (9.71 MJ kg −1 DM). There were no differences in weight gain of broiler chickens fed the commercial or laboratory prepared B. rapa and the yellow- and brown-seeded B. napus meals. Chickens fed B. juncea meal showed significantly lower feed intake and body weight gain which appeared to be attributed to a relatively high content of aliphatic glucosinolates in this particular meal (i.e., 21.7 μmol/g DM). Birds fed the yellow-seeded B. napus canola showed the lowest feed to gain ratio which averaged 1.51 and differed significantly from that of 1.59 and 1.61 for the commercial yellow-seeded B. rapa and the laboratory prepared brown-seeded B. napus canola, respectively.

Níveis de lisina digestível para frangos de corte machos na fase de 22 a 42 dias de idade

O objetivo deste experimento foi determinar a exigência de lisina digestível para frangos de corte machos no período de 22 a 42 dias de idade. Quatrocentos e cinqüenta frangos de corte machos Hubbard, com peso médio inicial de 631 g, foram distribuídos em delineamento experimental de blocos casualizados, com cinco tratamentos, seis repetições e 15 aves por unidade experimental. Os tratamentos corresponderam à ração basal com 19,64% de proteína bruta e 3100 kcal de EM/kg, suplementada com cinco níveis de L-lisina, resultando em rações com 0,80; 0,86; 0,91; 0,97; e 1,02% de lisina digestível. A digestibilidade verdadeira dos aminoácidos na dieta basal foi determinada por meio de ensaio de digestibilidade com galos Leghorn cecectomizados. Houve efeito dos níveis de lisina digestível da ração sobre ganho de peso (GP), consumo de ração, conversão alimentar (CA) e consumo de lisina, mas não houve efeito sobre a concentração de ácido úrico no soro sangüíneo, na composição química da carcaça e no rendimento de carcaça, incluindo rendimento de peito e coxa-sobrecoxa. Com base nos resultados de GP e CA, a exigência de lisina digestível foi estimada em 1,02 e 0,98%, respectivamente.

Níveis de lisina digestível para pintos de corte machos na fase de 1 a 21 dias de idade

O objetivo deste trabalho foi determinar a exigência de lisina digestível para pintos de corte machos na fase de 1 a 21 dias de idade. Seiscentos pintos de corte machos Hubbard, com peso médio inicial de 48 g, foram distribuídos em delineamento experimental em blocos casualizados, com cinco tratamentos, seis repetições e 20 aves por unidade experimental. Os tratamentos corresponderam à ração basal, com 20,85% de proteína bruta e 3000 kcal de EM/kg, atendendo às exigências de proteína, energia, cálcio, fósforo e aminoácidos, exceto lisina, suplementada com cinco níveis de L-lisina, resultando em rações com 0,84; 0,93; 1,02; 1,11; e 1,20% de lisina digestível na ração. A digestibilidade verdadeira dos aminoácidos na ração basal foi determinada por meio de ensaio de digestibilidade com galos Leghorn cecectomizados. Os níveis de lisina digestível da ração influenciaram o ganho de peso, a conversão alimentar, o consumo de lisina, o teor de extrato etéreo da carcaça e a taxa de deposição de proteína e gordura na carcaça. Porém, não houve efeito sobre o consumo de ração e na concentração de ácido úrico no soro sangüíneo e proteína bruta, matéria seca e água na carcaça. Com base nos resultados de GP, CA e taxa de deposição de proteína na carcaça, as exigências de lisina digestível foram estimadas em 1,05; 1,03; e 1,08%, respectivamente.

Nutritional evaluation of lectin-free soybeans for poultry

This study evaluated the nutritional value of raw lectin-free soybeans in comparison with raw Kunitz trypsin inhibitor-free soybeans, raw conventional soybeans, and commercial heat processed soybean meal (SBM). Analyzed lectin values (milligrams per kilogram) were 7.2, 7.1, and < 0.00015 for the Kunitz-free, conventional, and lectin-free soybeans, respectively. Three experiments were conducted using New Hampshire x Columbian male chicks fed 23% CP dextrose-soybean diets from 8 to 17 d of age. Growth performance of chicks fed lectin-free soybeans was greater (P < 0.05) than that of chicks fed raw conventional soybeans in all three experiments. However, performance of chicks fed lectin-free soybeans was lower than that of chicks fed Kunitz-free soybeans or SBM. The SBM yielded weight gains and feed efficiencies that were much higher than those observed from any of the raw soybeans. True amino acid digestibility and TMEn of the lectin-free and conventional soybeans were determined using the precision-fed cecectomized rooster assay. Seven roosters were crop-intubated with 30 g of soybeans and excreta were collected for 48 h. Digestibility coefficients of most amino acids for lectin-free soybeans were 5 to 8 percentage units higher than those for conventional soybeans, but the differences were not significant (P > 0.05). Likewise, the TMEn for lectin-free soybeans was 11% higher than that for raw conventional soybeans (3.577 vs 3.227 kcal/g DM) but the difference was not significant (P > 0.05). The results of this study indicate that the nutritional value of raw lectin-free soybeans is greater than raw conventional soybeans but is less than raw Kunitz-free soybeans and SBM, suggesting that trypsin inhibitor is a greater antinutritional factor than lectins.

Amino acid availability in poultry—in vitro and in vivo measurements

Methodology to evaluate the protein quality or amino acid availability in feed ingredients for poultry using in vitro (enzymic, chemical, or microbiological assays), indirect in vivo (plasma amino acid assays), or direct in vivo (growth or digestibility assays) measurements has been reviewed. The specific applications and limitations of these methods are examined. In vitro assays are useful in providing information on heat damage in selected protein sources under defined conditions, and on relative ranking of different samples, but they cannot form the basis of practical feed formulations. While growth assays remain the only direct means of confirming nutritional relevance of values obtained by other procedures, in vivo digestibility assays appear to be most useful, at present, to estimate amino acid availability. Amino acid digestibility assays in poultry should be based on the analysis of digesta from the terminal ileum rather than excreta, because of the variable and modifying effects of hindgut microflora. Techniques used to estimate endogenous amino acid losses in poultry are discussed. The needs for correction of endogenous losses in amino acid digestibility calculations and the relative merits of apparent and true digestible amino acid systems are still being debated. It is, however, clear that both digestible amino systems are superior to the total amino acid system currently employed to formulate practical diets. Digestible amino acid values are likely to form the basis of poultry feed formulations in the future. In particular, there is an urgent need for more precise information on the variation in digestible amino acid contents of locally grown ingredients and on the factors causing this variation (e.g. variety, location, season, agronomic practices, processing, etc.).

Effect of chemical composition of sunflower seed meal on its true metabolizable energy and amino acid digestibility

The effect of chemical composition of sunflower seed meal (SFSM) on TMEn and true amino acid digestibility (TAAD) was studied. In Experiment 1, the excretion pattern of three SFSM samples force-fed (30 g) to 10 adult cockerels (Hy-Line) each was followed for 84 h to determine the time interval for complete excretion of SFSM. Type of SFSM did not affect the excretion pattern of DM and energy (P=0.438, and P=0.189, respectively). Dry matter and energy excreted every 12 h decreased linear and quadratically (P < 0.001) with collection time. No differences were found from 48 h collection time on. So, an excreta collection period of 48 h was considered adequate for determining the TMEn of SFSM. In Experiment 2, 135 adult cockerels were force-fed to determine the TMEn of 11 samples of SFSM. Type of SFSM affected TMEn (P < 0.001), which ranged from 1,558 to 2,023 kcal/kg DM for SFSM of 31 to 42% CP, respectively. The TMEn was highly correlated (P < 0.001) to hemicellulose (r=-0.90), acid detergent lignin (r=-0.84), neutral detergent fiber (r=-0.82), and CP (r=0.77). Four prediction equations are proposed, the most practical being: TMEn (kcal/kg DM)=2,816.8 - 109.5 hemicellulose (%DM), RSD=70.2. Three out of the 11 samples of SFSM were selected for determining TAAD and the effect of endogenous amino acid correction. The methodology used was that of the TMEn assay, but one more estimation of amino acid endogenous excretion was made using a N-free diet with 85% cornstarch and 15% cellulose. Endogenous amino acid excretion was greater for roosters fed the N-free diet than those deprived of feed, resulting in a higher digestibility (from 0.7 to 2.7%, P < 0.05) only for six amino acids: threonine, valine, alanine, proline, and aspartic and glutamic acids. No interaction was detected (P=0.94) between type of SFSM and method of estimation of endogenous amino acid excretion. The TAAD of SFSM increased significantly (P < 0.001) with the CP content, total TAAD being 86, 88, and 89% for SFSM of 32, 35, and 37% CP, respectively. Attention should be paid when including high fiber-low protein SFSM in poultry diets to balance its lesser digestible amino acids contribution, mainly in lysine (from 0.77 to 1.06% for SFSM of 32 and 37% CP, respectively).

Availability of amino acids in high-oil corn

True digestibility of amino acids, bioavailability of Lys, and TMEn in three types of high-oil corn (HOC) and one conventional corn (CC) were determined. The CC, HOC1, HOC2, and HOC3 contained 4.3, 5.9, 6.6, and 9.5% ether extract, respectively, on a DM basis. True digestibility of amino acids was determined using the precision-fed cecectomized rooster assay in which each corn sample was tube-fed (30 g) to nine roosters and excreta were collected for 48 h. True digestibility of most amino acids in HOC2 and HOC3 were significantly higher (P < or = 0.05) than those in CC and HOC1. Mean digestibility of 15 amino acids in HOC2 and HOC3 was 91% compared to 80% for CC and HOC1. The TMEn values (kilocalories per gram DM) of CC, HOC1, HOC2, and HOC3 were 3.883, 4.024, 4.038, and 4.140, respectively. Lysine bioavailability was assessed using a slope-ratio chick growth assay in which a Lys-deficient crystalline amino acid diet was supplemented with 0, 0.1, or 0.2% L-Lys from L-Lys x HC1 to provide a standard curve. Six additional dietary treatments consisted of supplementing the basal diet with 28 or 56% of CC, HOC2, or HOC3. The nine diets were fed to four replicate groups of six chicks from 8 to 18 d posthatching. Lysine bioavailability was calculated using multiple regression slope-ratio methodology where Y was weight gain and X was intake of Lys from the L-Lys x HC1 or a corn. Supplementation of the basal diet with L-Lys x HC1, CC, HOC2, or HOC3 yielded linear (P < or = 0.001) growth responses. Bioavailability values (percentage) for the Lys in CC, HOC2, and HOC3 relative to the Lys in L-Lys x HC1 were 65 +/- 10, 72 +/- 10, and 91 +/- 8, respectively. The results of this study indicated that digestibility of amino acids and bioavailability of Lys in HOC are equal to or greater than those in CC.

Bioavailability of the digestible lysine and total sulfur amino acids in meat and bone meals varying in protein quality

Experiments were conducted to determine whether the digestible Lys, Met, and TSAA in a high and low quality meat and bone meal (MBM) were totally bioavailable for protein synthesis in chicks. True digestibility of amino acids (AA) in the two MBM was determined by the precision-fed cecectomized rooster assay. Bioavailability of the digestible AA was then assessed in three slope-ratio chick growth assays using Lys-, Met-, or TSAA-deficient crystalline AA basal diets that were supplemented with varying levels of the test AA, high or low quality MBM, or AA mixtures simulating the mean digestible AA composition of the high and low quality MBM. Response parameters were weight gain, feed efficiency, body N gain, and body Lys gain in the Lys assay and weight gain and feed efficiency in the Met and TSAA assays. Bioavailability values for the digestible Lys, Met, and TSAA in the MBM and AA mixtures simulating MBM varied depending on response parameter, with values based on feed efficiency generally being highest. No consistent differences in bioavailability of the digestible AA were observed between the two MBM when all AA were considered; however, the bioavailability of the digestible Lys in the low quality MBM was lower than that in the high quality MBM for two of four performance criteria. When considering all response parameters and the AA mixture results, bioavailability of the digestible Lys and Met in the two MBM was generally 90% or greater, whereas bioavailability of the digestible TSAA was only 80% or less. The results of this study indicated that essentially all of the digestible Lys and Met in MBM were bioavailable for protein synthesis and metabolism but suggested that a significant amount of the TSAA, particularly Cys, was not bioavailable.