Search

There is a real quest to develop reduced-crude protein diets to facilitate sustainable chicken-meat production. However, pronounced elevations in threonine plasma concentrations in systemic plasma have consistently been observed pursuant to crude protein reductions in diets for broiler chickens. The aim of the present Perspective was to consider the genesis and consequences of these elevated threonine concentrations. A series of five reduced-crude protein feeding studies with maize-based diets completed on the Camden Campus of Sydney University was the basis of the present Perspective. Collectively, an average reduction in dietary crude protein from 212 to 167 g/kg generated a mean increase of 64.8% (867 versus 526 μmol/L) in threonine plasma concentrations. This was attributed to the downregulation of hepatic threonine dehydrogenase activity, which catalyses threonine to acetyl-CoA and glycine and a mechanism for this inhibition is proposed. Tangible reductions in dietary crude protein usually impair feed conversion efficiency and increase fat deposition. Threonine plasma concentrations are elevated by these reductions and the likelihood is that threonine concentrations may be an indicative biomarker of the precision with which efficient reduced-CP broiler diets are formulated and, if so, would facilitate their successful development.

Global chicken-meat production is projected to expand substantially in the coming decades to meet demand. Given the drought-tolerant properties of sorghum, coupled with the challenges of climate ch...

Inclusions of non-bound amino acids particularly methionine, lysine and threonine, together with the “ideal protein” concept have allowed nutritionists to formulate broiler diets with reduced crude protein (CP) and increased nutrient density of notionally “essential” amino acids and energy content in recent decades. However, chicken-meat production has been projected to double between now and 2050, providing incentives to reduce dietary soybean meal inclusions further by tangibly reducing dietary CP and utilising a larger array of non-bound amino acids. Whilst relatively conservative decreases in dietary CP, in the order of 20 to 30 g/kg, do not negatively impact broiler performance, further decreases in CP typically compromise broiler performance with associated increases in carcass lipid deposition. Increases in carcass lipid deposition suggest changes occur in dietary energy balance, the mechanisms of which are still not fully understood but discourage the acceptance of diets with reductions in CP. Nevertheless, the groundwork has been laid to investigate both amino acid and non-amino acid limitations and propose facilitative strategies for adoption of tangible dietary CP reductions; consequently, these aspects are considered in detail in this review. Unsurprisingly, investigations into reduced dietary CP are epitomised by variability broiler performance due to the wide range of dietary specifications used and the many variables that should, or could, be considered in formulation of experimental diets. Thus, a holistic approach encompassing many factors influencing limitations to the adoption of tangibly reduced CP diets must be considered if they are to be successful in maintaining broiler performance without increasing carcass lipid deposition.

The contribution that exogenous phytases have made towards sustainable chicken-meat production over the past two decades has been unequivocally immense. Initially, their acceptance by the global industry was negligible, but today, exogenous phytases are routine additions to broiler diets, very often at elevated inclusion levels. The genesis of this remarkable development is based on the capacity of phytases to enhance phosphorus (P) utilization, thereby reducing P excretion. This was amplified by an expanding appreciation of the powerful anti-nutritive properties of the substrate, phytate (myo-inositol hexaphosphate; IP6), which is invariably present in all plant-sourced feedstuffs and practical broiler diets. The surprisingly broad spectra of anti-nutritive properties harbored by dietary phytate are counteracted by exogenous phytases via the hydrolysis of phytate and the positive consequences of phytate degradation. Phytases enhance the utilization of minerals, including phosphorus, sodium, and calcium, the protein digestion, and the intestinal uptakes of amino acids and glucose to varying extents. The liberation of phytate-bound phosphorus (P) by phytase is fundamental; however, the impacts of phytase on protein digestion, the intestinal uptakes of amino acids, and the apparent amino acid digestibility coefficients are intriguing and important. Numerous factors are involved, but it appears that phytases have positive impacts on the initiation of protein digestion by pepsin. This extends to promoting the intestinal uptakes of amino acids stemming from the enhanced uptakes of monomeric amino acids via Na+-dependent transporters and, arguably more importantly, from the enhanced uptakes of oligopeptides via PepT-1, which is functionally dependent on the Na+/H+ exchanger, NHE. Our comprehension of the phytate–phytase axis in poultry nutrition has expanded over the past 30 years; this has promoted the extraordinary surge in acceptance of exogenous phytases, coupled with the development of more efficacious preparations in combination with the deflating inclusion costs for exogenous phytases. The purpose of this paper is to review the progress that has been made with phytate-degrading enzymes since their introduction in 1991 and the underlying mechanisms driving their positive contribution to chicken-meat production now and into the future.

A total of 294 male, off-sex Ross 308 chickens were offered 7 dietary treatments with crude protein (CP) contents of 210, 195, 180, and 165 g/kg. One of the four 165 g/kg diet was consistent with the higher protein diets and 3 were modified to investigate the effects of increased methionine levels, pre-pellet inclusion of whole maize, and whey protein concentrate in reduced-CP broiler diets. There were 7 replicate cages, 6 birds per cage, from 14 to 35 D post-hatch. The average feed conversion ratio (FCR) of birds offered 210, 195, 180 g/kg CP diets was 1.555 which was superior (P < 0.05) to the 1.608 FCR of their 165 g/kg counterparts. The transition from 210 to 165 g/kg (diet 4) CP diets linearly increased (P < 0.001) relative fat-pad weights from 8.64 to 14.62 g/kg. The same transition linearly increased jejunal and ileal starch digestibility coefficients (P < 0.001), metabolizable to gross energy ratios (ME:GE) ratios (P < 0.001) and nitrogen (N)-corrected apparent metabolizable energy (AMEn) (P = 0.001) but did not influence N retention. Starch:protein disappearance rate ratios increased linearly (P < 0.001) from 2.68 to 3.82 in the jejunum and from 1.76 to 2.94 in the ileum following dietary CP reductions. Ileal disappearance rate ratios were quadratically related to FCR (r = 0.486; P < 0.005) and linearly related to relative fat-pad weights (r = 0.663; P < 0.001) where both parameters were disadvantaged by widening ratios. The transition from 210 to 165 g/kg crude protein diets linearly increased the average digestibility coefficient of 17 amino acids from 0.459 to 0.594 in jejunum and from 0.744 to 0.790 in the ileum. The present study demonstrates that dietary CP can be reduced from 210 to 180 g/kg without negatively influencing broiler performance but the further reduction to 165 g/kg compromised FCR. However, the three modifications to the 165 g/kg CP diet failed to enhance broiler performance.

SUMMARY The fundamental premise of starch and protein digestive dynamics is that an ideal balance of glucose and amino acids is made available at sites of skeletal muscle protein synthesis to promote efficient growth. Digestive dynamics involve the digestion of protein and starch in the gut lumen, absorption of glucose and amino acids along the small intestine and their transition across the gut mucosa into the portal circulation. However, the post-enteral, bilateral bioavailability of glucose and amino acids is ultimately dependent on their metabolic fates in enterocytes as both may be catabolized in avian enterocytes for energy to drive digestive processes. Importantly, digestive dynamics consider rates and sites of glucose and amino acid absorption along the small intestine in addition to their extents of digestion as determined by static digestibility coefficients. There is considerable interest in the development of low-protein/high-supplemental amino acid diets but the digestive dynamics of supplemental and protein-bound amino acids are inherently different. Therefore, the relevance of starch and protein digestive dynamics in poultry will become increasingly evident if low-protein diets are to be developed successfully in the future.

1.The objective of the present study was to rank the importance of the following dietary factors; canola meal, wheat, whole barley, digestible lysine, phytate-P, calcium, available P, sodium and three NSP-degrading feed enzymes. Their influence on growth performance, gastro-intestinal tract parameters, energy utilisation, ileal N digestibility and disappearance rates were determined via the Plackett-Burman design in broiler chickens offered phytase-supplemented diets. 2. The eleven dietary factors were assigned two levels in the Plackett-Burman design matrix. The resulting twelve dietary treatments were offered to six replicates per treatment (six birds per cage) with a total of 468 male Ross 308 broiler chicks from 7 to 28 d post-hatch. 3. Increasing digestible lysine levels improved weight gain by 15.6% (P

In this study the starch digestion rates in broiler chickens from 18 samples of 5 commonly used feed grains (sorghum, wheat, maize, barley, triticale) were determined. The methodology to determine starch digestion rates in poultry is detailed herein. Starch digestion rates were not significantly different (P = 0.128) across the 18 feed grains, which reflects the wide variations that were observed within a given feedstuff. Nevertheless, starch digestion rates in broiler chickens offered wheat-based diets were significantly more rapid by 56.0% (0.117 versus 0.075 min-1; P = 0.012) than their sorghum-based counterparts on the basis of a pair-wise comparison. In descending order, the following starch digestion rates were observed: wheat (0.117 min-1), barley (0.104 min-1), triticale (0.093 min-1), maize (0.086 min-1), sorghum (0.075 min-1). The implications of these findings are discussed as they almost certainly have implications for poultry nutrition and the development of reduced crude protein diets for broiler chickens.

Simple Summary There is a distinct possibility that synthetic and crystalline, or non-bound, amino acids will partially replace soybean meal in diets for broiler chickens and reduce the dependency of the chicken-meat industry on soybean meal as its principal source of protein. The genesis of this partial replacement will be the successful development of reduced-crude protein diets. A reduced-crude protein diet contains less soybean meal, and therefore less crude protein, but an increased array of essential and even non-essential non-bound amino acids so that requirements are met. There are, however, several challenges to be overcome if reduced-crude protein diets are to be successfully developed and adopted. Abstract This review explores the premise that non-bound (synthetic and crystalline) amino acids are alternatives to soybean meal, the dominant source of protein, in diets for broiler chickens. Non-bound essential and non-essential amino acids can partially replace soybean meal so that requirements are still met but dietary crude protein levels are reduced. This review considers the production of non-bound amino acids, soybeans, and soybean meal and discusses the concept of reduced-crude protein diets. There is a focus on specific amino acids, including glycine, serine, threonine, and branched-chain amino acids, because they may be pivotal to the successful development of reduced-crude protein diets. Presently, moderate dietary crude protein reductions of approximately 30 g/kg are feasible, but more radical reductions compromise broiler performance. In theory, an ‘ideal’ amino acid profile would prevent this, but this is not necessarily the case in practice. The dependence of the chicken-meat industry on soybean meal will be halved if crude protein reductions in the order of 50 g/kg are attained without compromising the growth performance of broiler chickens. In this event, synthetic and crystalline, or non-bound, amino acids will become viable alternatives to soybean meal in chicken-meat production.

The purpose of this review is to consider the distinct possibility that dietary non-bound and protein-bound amino acids are not bioequivalent in broiler chickens. Usually, with conservative inclusions of a limited number of non-bound (synthetic, crystalline, feed-grade) amino acids in standard broiler diets, bioequivalency would not be an issue. However, reduced-crude protein (CP) broiler diets demand substantial inclusions of an extended range of non-bound amino acids to meet amino acid requirements. A standard diet may contain 5.0 g/kg non-bound amino acids, but a reduced-CP diet may contain up to 50 g/kg and this relative abundance skews the balance of non-bound to protein-bound amino acids and substantial proportions of certain amino acids are present in diets as non-bound entities. Importantly, tangible reductions in dietary CP, for example from 210 to 160 g/kg, usually both compromise broiler growth performance and increase fat deposition. Compromised growth performance is more evident in wheat- than maize-based diets but, paradoxically, fat deposition is more apparent in maize-based diets. The inability of birds to accommodate tangible dietary CP reductions appears to stem partially from the lack of bioequivalency between non-bound and protein-bound amino acids because of the differentials in intestinal uptake rates. Also, reduced-CP broiler diets generate perturbations in apparent amino acid digestibility coefficients which compound the fact that intestinal uptakes of non-bound acid acids are more rapid, and occur more anteriorly in the small intestine, than protein-bound amino acids. The likelihood is that greater proportions of non-bound amino acids transit the enterocytes of the gut mucosa without entering anabolic and/or catabolic pathways to gain entry to the portal circulation. This culminates in post-enteral amino acid imbalances and postprandial oxidation of surplus amino acids which involves deamination of amino acids and elevations in plasma ammonia (NH3) concentrations, but NH3 is inherently toxic and demands detoxification. Excessive deamination coupled with inadequate detoxification could result in 'ammonia overload' which would be expected to compromise growth performance. Thus, the hypothesis is that non-bound and protein-bound amino acids are not bioequivalent; moreover, it may be argued that this distinction is being overlooked and is thwarting the development and acceptance of reduced-CP broiler diets.

A total of 288 day-old, male Ross 308 chicks were offered six dietary treatments from 7 to 28 days post-hatch. A standard maize-soy diet was compared with five low protein diets containing high inclusions of maize starch and various combinations of supplemental amino acids. The assessed parameters included growth performance, nutrient utilisation, digestibility coefficients and disappearance rates of starch, protein and amino acids in four small intestinal segments. Also, the effects of three dietary treatments on free plasma amino acid concentrations in the anterior mesenteric vein or portal circulation were determined. The transition from standard to low protein diets elevated feed intakes and compromised FCR. Overall, tangible differences in responses were not observed in birds offered the five low protein diets which effectively precluded meaningful comparisons between the various combinations of crystalline amino acids. Maize starch inclusions in low protein diets enhanced starch digestibility coefficients and disappearance rates and parameters of nutrient utilisation. However, maize starch also depressed protein digestibility coefficients and disappearance rates. Moreover, amino acid digestibility coefficients were depressed in the three posterior segments of the small intestine. Instructively, proximal ileal starch digestibility coefficients were negatively correlated with digestibility coefficients of twelve amino acids in the proximal ileum to significant extents. Significant differences in concentrations of free amino acids in plasma from the anterior mesenteric vein were observed for histidine, lysine, methionine, threonine and valine in birds offered the standard and two low protein diets. The possibility that glucose and amino acids were effectively competing for intestinal uptakes, especially from the ileum, is discussed. Also, it appears that the metabolic fates of amino acids in enterocytes of the gut mucosa can be manipulated by dietary strategies and that crystalline amino acids may be less prone to undergo catabolism in the gut mucosa.

Each of eight dietary treatments was offered to seven replicates (six birds per cage) of male Ross 308 chicks from 7 to 28 days post-hatch. The diets contained 741 g/kg wheat incorporated as ground (3.2 mm hammer-mill screen) wheat or 125 g/kg whole wheat included in diets, either pre- or post-pelleting. In Experiment 1 of the study, ground grain, pre-pellet and post-pellet whole grain diets were offered with and without phytase as a 3 × 2 factorial array of treatments. The effects of dietary treatments on gizzard and pancreas weights, bone mineralisation, excreta dry matter, growth performance, nutrient utilisation, digestibility coefficients and disappearance rates of starch and protein (N) in four small intestinal segments were determined. Post-pellet whole grain addition significantly increased gizzard weight by 12.5% (18.17 versus 16.15 g/kg; P

A total of ten experimental diets with protein concentrations ranging from 154 to 400 g/kg and two lipid levels (46 and 85 g/kg) with identical energy densities were offered to 240 male Ross 308 broilers from 7 to 28 d post-hatch. Growth performance was monitored and nutrient utilisation (apparent metabolisable energy (AME), N-corrected AME (AMEn), AME daily intake, AME:gross energy ratios, N retention) was determined. The weight gain response of broiler chickens to dietary protein concentrations in diets containing high and low lipid levels was diverse, with the relevant quadratic regressions being significantly different (PP>0·05). AMEn was also linearly (PPr 0·933, PR2=0·93, P

This study comprised a 2 × 2 factorial array of dietary treatments offered to male Ross 308 broiler chicks from 15 to 28 days post-hatch. The dietary treatments consisted of a sorghum-soybean meal diet in which either sorghum was partially substituted by maize starch (200 g/kg) or soybean meal was partially substituted by fishmeal (175 g/kg). Growth performance, nutrient utilisation, digesta retention times in four small intestinal segments, starch and protein (N) digestibility coefficients and disappearance rates (g/bird/day) and starch:protein disappearance rate ratios in four small intestinal segments were determined. The partial substitution of soybean meal by fishmeal had the more profound effects on the parameters assessed as fishmeal inclusions improved weight gain by 12.1% (1260 versus 1124 g/bird, P

Thirteen extensively characterised grain sorghum varieties were evaluated in a series of 7 broiler bioassays. The efficiency of energy utilisation of broiler chickens offered sorghum-based diets is problematic and the bulk of dietary energy is derived from sorghum starch. For this reason, rapid visco-analysis (RVA) starch pasting profiles were determined as they may have the potential to assess the quality of sorghum as a feed grain for chicken-meat production. In review, it was found that concentrations of kafirin and total phenolic compounds were negatively correlated with peak and holding RVA viscosities to significant extents across 13 sorghums. In a meta-analysis of 5 broiler bioassays it was found that peak, holding, breakdown and final RVA viscosities were positively correlated with ME:GE ratios and peak and breakdown RVA viscosities with apparent metabolizable energy corrected for nitrogen (AMEn) to significant extents. In a sixth study involving 10 sorghum-based diets peak, holding and breakdown RVA viscosities were positively correlated with ME:GE ratios and AMEn. Therefore, it emerged that RVA starch pasting profiles do hold promise as a relatively rapid means to assess sorghum quality as a feed grain for chicken-meat production. This potential appears to be linked to quantities of kafirin and total phenolic compounds present in sorghum and it would seem that both factors depress RVA starch viscosities in vitro and, in turn, also depress energy utilisation in birds offered sorghum-based diets. Given that other feed grains do not contain kafirin and possess considerably lower concentrations of phenolic compounds, their RVA starch pasting profiles may not be equally indicative.

Previous experimentation has indicated that wheat-based diets are a poor diet type to allow for optimal performance when dietary crude protein (CP) is reduced, while corn-based diets show promise. Potential mitigation of the negative effects associated with reduced CP wheat-based diets could include blending corn and wheat to be used as the cereal grain portion of broiler diets. Therefore, two studies were conducted in order to observe the effects of reduced dietary CP when broilers were fed diets containing a 1:1 blend of wheat and corn. For Experiment 1, 816 Cobb 500 broilers were placed in 24 floor pens to allow for the observation of live performance measurements from 1–41 days of age, and 108 Ross 308 broilers were placed into 18 battery cages for observation of protein and nutrient digestibility from 8–28 days of age in Experiment 2. In the floor pen study, High and Low diets were formulated to contain 235, 215, and 195 and 195, 175, and 155 g/kg CP in the starter, grower, and finisher diets, respectively. The High and Low diets were then blended to produce a Medium diet containing 215, 195, and 175 g/kg CP in the starter, grower, and finisher diets, respectively. Alternately, grower diets were offered to broiler chickens raised in battery cages from day 8–28 in Experiment 2. No effects of reduced CP were found on final body weight (BW), BW gain, or feed intake for any growout period in Experiment 1 but feed conversion ratio (FCR) was significantly increased for broilers fed the Low CP diet compared to broilers fed the High and Medium diets for the 1–27 and 1–41 day periods. In Experiment 2, broilers fed the Low diet achieved lower final BW, BW gain, and feed intake than those fed the High and Medium diets. Feed conversion ratio increased in a stepwise manner as CP was reduced. Nutrient digestibility assays found stepwise increases in nitrogen-corrected apparent metabolisable energy (AMEN) as dietary CP level was reduced and increased nitrogen (N) digestibility for broilers fed the Medium and Low diets compared to those fed the High. These data indicated that including wheat and corn at a 1:1 ratio in reduced CP diets was able to adequately support final BW and BW gain in floor pens.

The hypothesis that maize-based diets for broiler chickens are more conducive to crude protein reductions than wheat-based diets was examined. A total of 324 male, off-sex (parent line) Ross 308 chicks were offered nine experimental diets from 7 to 35 days post-hatch as a 3 × 3 factorial array of dietary treatments. The design included three levels of dietary crude protein (CP) of 222, 193 and 165 g/kg and three feed grains: maize, ground wheat, and whole wheat (150 g/kg added post-pelleting). The determined parameters included growth performance, relative gizzard and abdominal fat-pad weights, nutrient utilisation, water and feed intakes over the total collection period and excreta dry matter, apparent ileal digestibility coefficients and disappearance rates of starch, protein (N) and amino acids (n = 15), concentrations of free amino acids (n = 20) in systemic plasma, and Pearson correlations between apparent ileal digestibility coefficients of neutral amino acids. The growth performance of birds offered the 165 g/kg CP maize-based diet was very acceptable relative to their 222 g/kg CP counterparts with significant advantages of 7.05 % in weight gain (2370 versus 2214 g/bird), 8.51 % in feed intake (3481 versus 3208 g/bird) and a numerical disadvantage of 1.38 % (1.473 versus 1.453) in FCR. In contrast, 165 g/kg CP ground wheat-based diets supported highly unsatisfactory growth performances. In comparison to 222 g/kg CP wheat-based diets, there were pronounced disadvantages of 35.5 % (1549 versus 2403 g/bird) in weight gain, 18.5 % (2843 versus 3487 g/bird) in feed intake and 26.6 % (1.840 versus 1.453) in FCR. Thus, the hypothesis that maize-based diets are more conducive to CP reductions than wheat-based diets was unequivocally established. While it is not straightforward, the genesis of the inferiority of wheat relative to maize in this context is considered against the background of the observations recorded in the present study.

The objective was to investigate the effects of 500 and 2000 FTU/kg phytase inclusions in maize–based diets with appropriately reduced nutrient specifications in comparison to a positive control diet. Diets were offered to Ross 308 broiler chickens from 7 to 28 days post-hatch and growth performance, nutrient utilisation parameters, sodium, starch and protein (N) digestibility coefficients were obtained in four small intestinal segments and IP6 phytate degradation coefficients were determined in the gizzard and in four small intestinal segments. The transition from positive control to negative control diets compromised weight gains, FCR and toe ash by 10.3%, 6.57% and 11.5%, respectively. However, 2000 FTU/kg phytase supplementation completely restored these parameters. At 500 FTU/kg phytase significantly increased starch digestibility coefficients by 12.7% (0.879 versus 0.780) in the distal jejunum and by 4.41% (0.947 versus 0.907) in the proximal ileum and significantly increased starch disappearance rates in all four small intestinal segments. Significant increases in protein (N) digestibility and disappearance rates were limited to the proximal ileum where 500 FTU/kg phytase increased protein (N) digestibility coefficients by 6.08% (0.785 versus 0.740). Phytase, at both inclusions, significantly increased the recovery of sodium in the three anterior small intestinal segments. Interestingly, sodium digestibility coefficients were correlated (P = 0.051 −

1. The two red grain sorghums were extensively characterised. Kafirin, polyphenolic compounds, free, conjugated and bound phenolic acids, phytate concentrations and starch pasting profiles were determined. 2. The experiment consisted of a 2 × 4 factorial array of dietary treatments comprising two red sorghum varieties (Tiger and Block I) ground through 4 hammer-mill screen sizes (2.0, 3.2, 4.8 6.0 mm) prior to incorporation into nutritionally equivalent diets. Eight steam-pelleted dietary treatments were each offered to 7 replicates (6 male Ross 308 birds per cage) from 7 to 28 d post-hatch. 3. Effects of dietary treatments on growth performance, relative gizzard and pancreas weights, nutrient utilisation, apparent starch and protein (N) digestibility coefficients and disappearance rates from 4 small intestinal segments were determined. 4. The 2.0-mm hammer-mill screen generated an average geometric mean particle size of 794 μm and the 6.0-mm screen a mean particle size of 1405 μm. However, hammer-mill screen size did not influence weight gain or FCR. The 6.0-mm screen size generated significantly higher starch and protein (N) digestibility coefficients in the distal jejunum and distal ileum than the 2.0-mm hammer-mill screen. 5. Tiger sorghum was superior to Block I sorghum, as significant advantages were observed for feed conversion ratios (3.25%), AME (0.37 MJ), ME:GE ratios (4.15%), AMEn (0.53 MJ), distal ileal starch digestibility coefficients (2.46%) and protein (N) digestibility coefficients in the distal jejunum (4.66%), proximal ileum (1.96%) and distal ileum (2.16%). The inferior Block I sorghum contained more kafirin (67.1 versus 51.3 g/kg), phytate (9.79 versus 8.40 g/kg), total phenolic compounds (4.68 versus 4.12 mg GAE/g), flavan-4-ols (7.98 versus 5.04 ABS/ml/g), total phenolic acids (554 versus 402 μg/g) and total ferulic acid (375 versus 281 μg/g) in comparison to Tiger sorghum.

A feeding study with a Box-Behnken response surface design was completed to investigate the influence of starch and protein digestive dynamics on growth performance and nutrient utilisation under different durations of feed access. The design comprised three feed access durations (6, 15 and 24 h), three fishmeal inclusion rates (0, 87.5, 175 g/kg) and three corn starch inclusion rates (0, 100, 200 g/kg) in broiler diets based on sorghum and soybean meal. Each of thirteen dietary treatments was offered to 5 replicates of 6 birds per replicate or a total of 65 cages and 390 Ross 308 male and female chicks (50-50, feather-sexed) from 15 to 28 days post-hatch. Duration of feed access had the greatest impact on weight gain and feed conversion ratio (FCR). Both weight gain and feed conversion efficiency were improved with increasing feed access duration. At each level of feed access duration, FCR was improved with increasing fishmeal inclusion, whereas corn starch inclusion had little impact on FCR. Nitrogen retention was influenced by duration of feed access but not by fishmeal or corn starch. The predicted minimum N retention 52.38% equated to a feed access of 17.45 h duration. N retention decreased with feed access duration when feed access was less than 17.45 h and then improved with feed access duration when feed access was longer than 17.45 h. The predicted maximum feed intake of 1720 g/bird equated to a feed access of 22.00 h duration. It is noteworthy that birds with 24 h access to feed had significantly higher total feed intake but significantly lower hourly intake (P

The objective of this study was to examine the influence of meat-and-bone meal (MBM) and phytase inclusion on growth performance, bone mineralisation and apparent digestibility coefficients of nutrients in broiler chickens offered wheat-based diets. The feeding study comprised 7 dietary treatments: positive control (PC, 9.0% Ca and 4.5% available phosphorous [AvP] in starter, 7.0% Ca and 3.5% AvP in finisher); negative control (NC, 7.2% Ca and 3.0% AvP in starter, 5.2% Ca and 2.0% AvP in finisher) diets incorporating a 3 × 2 factorial array of 3 MBM inclusions (0, 60, 120 g/kg) and 2 levels of phytase supplementation (0 and 1,000 FYT/kg). Each treatment was allocated to 6 replicated pens with 30 birds per pen in an environmentally-controlled deep litter facility. A total of 1,260 one-day-old male Ross 308 chicks were offered starter diets from 1 to 14 days post-hatch and finisher diets from 15 to 36 days post-hatch. There were significant (P

Data pertaining to the branched-chain amino acids (BCAA) are of particular importance due to the positioning of valine (Val) and isoleucine (Ile) as limiting amino acids (AA) in conventional diets. Similarly, current research evaluating their potential interaction is sparse. Therefore, two experiments were conducted using Box-Behnken design (BBD) to determine performance and carcass responses to BCAA and glycine (Gly) supplementation in male broilers from 15–34 days (Experiment 1) and 15–35 days (Experiment 2). In Experiment 1, 13 experimental diets were formulated to contain various levels of digestible BCAA supplementation based on BBD. Inclusion levels for the BCAA were based on ratios to digestible lysine (Lys) and included: 65, 75, and 85 for digestible Val; 58, 66, and 74 for digestible Ile; and 110, 130, and 150 for digestible leucine (Leu). Diets for Experiment 2 were formulated in a similar manner and design, but total glycine + serine (Gly + Ser) inclusions were substituted for Leu. Inclusion levels were the same for Val and Ile as in Experiment 1 and ratios to digestible Lys of 131, 151, and 171 for total Gly + Ser. Fifteen-hundred and sixty male broilers were distributed across 78 pens and randomly assigned to 13 experimental diets in each Experiment. Body weight (BW) gain, feed intake, and feed conversion ratio (FCR) were determined for the experimental grower period in both Experiments. On day 35 (Experiment 1) or 36 (Experiment 2), six birds per pen were processed for the evaluation of carcass traits. Data were analyzed for linear, quadratic, and interactive effects. In Experiment 1, increased Leu inclusion linearly increased (P

A study evaluating apparent digestibilities of protein and amino acids and their corresponding digestion rates in four small intestinal sites in broiler chickens was completed to further investigate dietary optimisation via synchronised nutrient digestion and absorption. A total of 288 male Ross 308 broiler chickens were offered semi-purified diets with eight protein-rich feedstuffs, including; blood meal (BM), plasma protein meal (PPM), cold pressed (CCM) and expeller-pressed (ECM) canola meal, high (SBM HCP) and low (SBM LCP) crude protein soybean meals, lupins and peas. Diets were iso-caloric, iso-nitrogenous and the test ingredient was the sole source of dietary nitrogen. Each diet was offered to 6 bioassay cages with 6 birds per cage from day 21 to 28 post hatch. On day 28, all birds were euthanized and digesta samples were collected from the proximal jejunum, distal jejunum, proximal ileum and distal ileum to determine apparent protein and amino acids digestibility coefficients, digestion rates and potential digestible protein and amino acids. Dietary protein source significantly influenced energy utilisation, nitrogen retention, apparent protein (N) digestibilities, digestion rates and potential digestible protein along the small intestine. Diets containing BM and SBM LCP exhibited the highest protein digestion rate and potential digestible protein, respectively. Digestibility coefficients and disappearance rates of the majority of amino acids in four sections of the small intestine were influenced by dietary protein source (P < 0.01) and blood meal had the fastest protein digestion rate. In general, jejunal amino acid and protein digestibilities were more variable in comparison to ileal digestibilities, and the differences in protein and amino acid disappearance rates were more pronounced between types of feedstuffs than sources of similar feedstuffs.

A study was conducted to compare maize, wheat and sorghum as the main feed grain in standard phytase and xylanase supplemented diets for broiler chickens. Six diets with different grain varieties (two wheat, two sorghum and two maize) were formulated in accordance with Ross 308 recommendations for starter, grower and finisher diets and were offered from 1 to 10, 11–26 and 27–35 days post-hatch, respectively. The six treatments were offered to 672 male Ross 308 chicks, with eight replicate cages per treatment and 14 birds per cage from 1 to 10 days post-hatch and 6 birds per cage from 11 to 35 days post-hatch. Over the 1–35 day experimental period, birds offered diets based on maize B generated the most efficient feed conversion ratio (FCR, 1.380), whereas birds offered red sorghum-based diets generated the poorest FCR (1.478). Likewise, in the finisher phase, birds offered both maize and wheat generated significantly greater apparent metabolisable energy (AME, MJ/kg DM), AME to gross energy ratio (AME:GE, MJ/MJ) and nitrogen corrected AME (AMEn, MJ/kg DM) than birds offered sorghum-based diets. Birds offered diets containing wheat A generated the greatest starch digestibility coefficient in the jejunum and ileum in both starter and finisher diets and red sorghum outperformed white sorghum in terms of AME and starch digestibility. In the ileum, broiler chickens offered finisher diets based on wheat B had the highest protein digestibility. In conclusion, birds offered maize-based diets achieved the best growth performance and energy utilisation followed by birds offered wheat- and sorghum-based diets.

Off-sex, male Ross 308 chickens were offered maize-soy diets without and with 3.5 g/kg lysine monohydrochloride (HCl), which contained 10.0 or 12.8 g/kg digestible lysine, from 7 to 28 D post-hatch. Birds were permitted access to diets at intervals of 12, 16, and 20 h/day. Lysine HCl improved weight gain (1,465 vs. 1,417 g/bird; P0.025) and feed conversion ratios (1.351 vs. 1.382; P0.005). Extending feed access intervals increased weight gain (1,542 vs. 1,303 g/bird; P0.001) and feed intake (2,142 vs. 1,748 g/bird; P0.001) but compromised feed conversion ratios (1.390 vs. 1.342; P0.001). Extending feed access intervals increased (P0.001) both relative crop and gizzard weights and amounts of digesta retained in these organs. Effective lysine HCl utilization in poultry irrespective of feeding frequency, as opposed to pigs, may stem from anticipatory feeding behavior, crop and gizzard functionality, and increased episodes of reverse peristalsis. Collectively, these properties appear to modulate the relative intestinal uptakes of unbound lysine and protein-bound amino acids including lysine. Instructively, extending daily feed access intervals from 12 to 20 h increased average ileal digestibility coefficients of 16 amino acids by 12.8% (0.830 vs. 0.736; P0.001), which was linearly related (r = -0.834; P0.001) to hourly feed intake rates. Birds given 12 h feed access consumed relatively more feed on an hourly basis and this may have contributed to lesser amino acid digestibilities. As treatment interactions (P0.35) between lysine HCl and feed access intervals for parameters of growth performance were not observed, it was concluded that feed access intervals do not influence lysine utilization. The implications of these findings are discussed.

Maize-based diets were formulated to contain 208, 193, 179 and 165 g/kg crude protein (CP) were prepared and the last diet was supplemented with 4.33 g/kg glycine equivalents and 1.10 g/kg threonine, individually and in combination, to provide seven dietary treatments. Each dietary treatment was offered to eight replicate cages (6 birds per cage) of off-sex, male Ross 308 chickens from 7 to 35 days post-hatch. The transition from 208 to 165 g/kg CP diets numerically compromised weight gain and feed conversion ratios (FCR) by 5.41% and 3.44%, respectively, and linearly increased relative fat-pad weights from 7.62 to 13.31 g/kg. The same transition linearly increased ileal starch:protein disappearance rate ratios from 2.01 to 3.23 (r = -0.823; P

A total of 336 off-sex, male Ross 308 chicks were offered seven dietary treatments from 7 to 35 days post-hatch; each treatment was offered to eight replicate cages with six birds per cage. Three wheat-based diets were formulated to declining crude protein (CP) levels of 215, 190 and 165 g/kg but with a constant energy density (12.70 MJ/kg), electrolyte balance (250 mEq/kg) and digestible lysine level (11.00 g/kg). In a 2 × 3 factorial arrangement birds were offered either 215 or 165 g/kg CP diets to which 0%, 12.5% and 25.0% whole gain was incorporated post-pelleting. In addition, a ground grain, 190 g/kg CP diet served as a seventh treatment. The assessed parameters included growth performance, relative gizzard, pancreas and abdominal fat-pad weights, nutrient utilisation, concentrations of free amino acid in portal (anterior mesenteric vein) and systemic (brachial vein) plasma and apparent jejunal and ileal amino acid digestibility coefficients and disappearance rates. The CP reduction from 215 to 165 g/kg compromised FCR by 5.99% (1.576 versus 1.487; P

Concentrations of polyphenolic compounds and free, conjugated and bound phenolic acids were determined in six red grain sorghum varieties harvested on the Liverpool Pains in 2009. Categories of polyphenolic compounds quantified included total phenolics, anthocyanins, flavan-4ols, luteolinidin, apigeninidin, 5-methoxy-luteolinidin, 7-methoxy-apigeninidin, apigenin, luteolin, eriodictyol and naringenin. Phenolic acids that were quantified included p-hydroxybenzoic, vanillic, caffeic, p-coumaric, ferulic, syringic and sinapic acids. These sorghums were also extensively characterised for additional properties including rapid visco-analysis (RVA) of starch pasting profiles, protein solubility and quantification of kafirin and phytate. A pigmented testa was not detected in the six varieties by the quantal Clorox bleach test, which indicated that they were Type I sorghums that do not possess condensed tannin. This was confirmed by vanillin assays. The six varieties were incorporated into unprocessed sorghum–casein mash diets and offered to broiler chickens to compare nutrient utilisation parameters and protein (N) digestibility coefficients. One objective of this study was to assess if non-tannin phenolic compounds influence energy utilisation in broiler chickens. Negative correlations between certain conjugated phenolic acids in sorghum and parameters of energy utilisation (AME, ME:GE ratios, AMEn) in birds were observed. For example, p-coumaric (r = −0.826), ferulic (r = −0.831) and total conjugated phenolic acids (r = −0.832) were negatively correlated with ME:GE ratios to significant (P

The effects of the 500 FTU/kg inclusion of Buttiauxella phytase in maize-based broiler diets were investigated where each treatment consisted of eight replicates of six male Ross 308 chicks per cage. Apparent digestibility coefficients of starch, sixteen amino acids and nine minerals in four small intestinal segments were determined in broilers offered P-adequate, maize-based diets at 40 days post-hatch. The disappearance rates of starch and protein (the sum of amino acids) from the four small intestinal segments were calculated and starch:protein disappearance rate ratios deduced in order to assess the effects of phytase on digestive dynamics. Phytase increased starch digestibility coefficients in the proximal jejunum (0.681 versus 0.538; P = 0.001) and distal ileum (0.959 versus 0.936; P = 0.009) and starch disappearance rates in the proximal jejunum (58.0 versus 43.4 g/bird/day; P = 0.004) and proximal ileum (80.8 versus 71.4 g/bird/day; P = 0.036). Phytase significantly increased (P = 0.003 –

Starter, grower and finisher maize-based diets (Diets A) were formulated to marginal nutrient specifications and offered to broilers from 1 to 14, 15 to 27, and 28 to 40 days post-hatch, respectively. Nutrient specifications were reduced (Diets B) and offered to broilers without and with 500 FTU/kg phytase; specifications were further reduced to create a second tier of reduced nutrient specifications (Diets C) without and with 1000 FTU/kg phytase. The study was conducted using 240 male Ross 308 chicks with each of the 5 treatments consisting of 8 replicates of 6 birds per replicate. Growth performance was monitored during each phase of the grow-out period, mineral retentions were determined in the grower phase and nutrient utilisation in the finisher phase. Apparent digestibility coefficients of nitrogen were determined in the proximal jejunum, distal jejunum, proximal ileum and distal ileum in broilers at 40 days post-hatch. In addition, N digestion rates ( K nitrogen ) were determined. Over the 40-day feeding period, declining nutrient specifications decreased weight gains in broilers offered non-supplemented diets from 2721 (Diets A) to 2627 (Diets B) and 2525 g/bird (Diets C) and increased FCR from 1.551 to 1.577 and 1.605 in the corresponding diets. The differences in weight gain (7.20%) and FCR (3.48%) between Diets A and Diets C were significant ( P P P P P P P P P P P P K nitrogen ) of 64% from 2.59 to 4.24 × 10 −2 min −1 . Phytase supplementation of diets C increased N digestibility in the distal ileum by 7.63% ( P −2 min −1 ( P

The hypothesis that glucose and amino acids should be made available in appropriately balanced quantities at the sites of protein synthesis for efficient protein deposition and growth performance i...

A foundation diet, an intermediate blend and a summit diet were formulated with different levels of soyabean meal, casein and crystalline amino acids to compare ‘slow’ and ‘rapid’ protein diets. The diets were offered to male Ross 308 chicks from 7 to 28 d post-hatch and assessed parameters included growth performance, nutrient utilisation, apparent digestibility coefficients and disappearance rates of starch and protein (N) in four small intestinal segments. Digestibility coefficients and disappearance rates of sixteen amino acids in three small intestinal segments and amino acid concentrations in plasma from portal and systemic circulations from the foundation and summit diets were determined. The dietary transition significantly accelerated protein (N) disappearance rates in the distal jejunum and ileum. The transition from foundation to summit diets significantly increased starch digestibility coefficients in the ileum and disappearance rates in all four small intestinal segments. These starch responses were associated with significant enhancements in nutrient utilisation. The dietary transition linearly increased digestibility coefficients and disappearance rates of amino acids in the majority of cases. The summit diet increased plasma concentrations of five amino acids but decreased those of four amino acids relative to the foundation diet to significant extents. Plasma concentrations of free amino acids were higher in the portal than systemic circulations. Rapid protein disappearance rates advantaged poultry performance and influenced post-enteral availability of amino acids. If the underlying mechanisms are to be identified, further research into the impact of protein digestive dynamics on broiler performance is required but appears justified.

1. The objective was to compare three whole grain (WG) inclusion levels (7.5, 15 and 30%) offered to broiler chickens by three modes of WG incorporation: (i) pre-pellet WG inclusion, (ii) post-pellet WG inclusion as a blend of WG and pelleted concentrate and (iii) post-pellet WG inclusion where WG and pelleted concentrate were provided in separate feed trays against a ground-grain, wheat-based control diet. 2. Ten dietary treatments were offered to 6 replicate cages (6 birds per cage) of male Ross 308 chickens from 7 to 28 d post-hatch. The effects of treatment on relative gizzard weights, gizzard contents, pancreatic weights and pH of gizzard digesta were monitored. Parameters of growth performance, nutrient utilisation (apparent metabolisable energy [AME], metabolisable to gross energy [ME:GE] ratios, nitrogen [N] retention and N-corrected AME [AMEn]), apparent starch and protein (N) digestibility coefficients and disappearance rates in for small intestinal segments and concentrations of free amino acids in plasma taken from the anterior mesenteric vein were determined. 3. Whole grain feeding (WGF) did not influence weight gain, but 30% post-pellet blended and 15 and 30% post-pellet separated treatments significantly depressed (P

Context Cereal grains used by the poultry industry in Australia vary widely in available energy and protein content, which is often reflected as variation in bird performance. Rapid or real-time techniques for measuring the apparent metabolisable energy (AME) content of cereal grains for birds include near infrared spectroscopy, rapid visco-analysis starch pasting profiles and colour analysis. Aims This study involved retrospective colour analysis of Australian sorghum samples reported in recent publications, and sorghum samples used in commercial production of chicken meat in Australia. The main objective was to develop regression models as tools to predict AME values for sorghum from colour analysis of the grain for timely assistance to nutritionists formulating commercial diets and purchasing sorghum grain. Methods Stepwise regression analysis was used to correlate AME values for 18 samples of red, yellow and white sorghum with their CIELAB colour variables L*, a* and b*, which indicate lightness (from black to white), green-red component and blue-yellow component, respectively. The model was then used to predict AME values for sorghum in previously reported studies. Key results The multivariate model AMEsorghum (MJ/kg DM) = 31.139 – 0.189 L* – 0.604 a* + 0.189 b* (P = 0.0021, R2 = 0.638) was shown to predict AME of red sorghum samples to within an average difference of 0.67 MJ/kg DM in one published study. The sorghum sample showing the largest difference contained kafirin 61.5 g/kg. Data from another published study indicated larger differences (0.93 MJ/kg DM) between predicted and measured values for sorghum. The largest difference of 1.41 MJ/kg DM was observed for a sample of white sorghum containing the lowest concentrations of kafirin (41.4 g/kg), phytate (4.93 g/kg) and total phenolics (3.00 mg GAE/g). Conclusions CIELAB colour analysis has potential as a rapid, inexpensive indicator of AME values for sorghum as a feed grain for chicken-meat production, but high concentrations of antinutritive components, such as kafirin, detract from this potential. Implications A rapid, inexpensive indicator of kafirin, such as near infrared, is required to complement CIELAB colour analysis.

The effects of phytase supplementation on growth performance, nutrient utilisation, starch and protein digestive dynamics in broiler chickens offered maize-, sorghum- and wheat-based diets were determined in a previous study (Liu et al., 2014). Responses to phytase were most pronounced in maize-based diets, which suggest that more phytate was degraded in these diets. Relevant retained samples of grain, diets and digesta from four small intestinal segments were retrospectively analysed for concentrations of phytate, sodium and starch pasting properties to investigate the hypothesis that phytate in maize-based diets was more completely degraded by exogenous phytase. Exogenous phytase significantly (P

To investigate the effects of phytase supplementation on growth performance, nutrient utilization and digestive dynamics of starch and protein, a study was conducted using 288 male Ross 308 chicks (6 treatments with 8 replicate cages of 6 birds). Birds were offered steam-pelleted diets based on maize, sorghum or wheat, without or with phytase supplementation, from 7 to 27 days post-hatch. Experimental diets were formulated to be equivalent for energy, protein/amino acids and were P-adequate. Digesta samples from proximal jejunum, distal jejunum, proximal ileum and distal ileum were collected in their entirety at day 27. Digestion rates of starch and protein were determined by fitting exponential mathematical model to apparent digestibility coefficients with mean retention times in each small intestinal segment. The growth performance of birds offered maize and sorghum were comparable but those offered wheat-based diets were inferior. Phytase improved weight gain (P 0.05), but it significantly increased disappearance rates of starch in maize-based diets (P

The effects of sorghum grain variety and conditioning temperature at which broiler diets were steam-pelleted on small intestinal digestion dynamics of starch and nitrogen were assessed. A 2×3 factorial array of treatments comprised two sorghum varieties, with white (Liberty) and red (Venture) pericarps and three conditioning temperatures (70, 80, 90°C). Both sorghums were finely-ground through a 2.0 mm hammer-mill screen prior to incorporation into the diets. Each of the dietary treatments was offered to six replicate cages (6 birds per cage) from 7 to 28 days post-hatch. Digesta samples were collected at day 28 for determination of starch and nitrogen digestibilities and mean retention time in the proximal jejunum, distal jejunum, proximal ileum and distal ileum. The digestion dynamics of starch and nitrogen were determined using an exponential mathematical model to relate digestion coefficients with mean retention times in each small intestinal segment. Increasing conditioning temperatures generated a 'concav e response' in starch digestion rates in white sorghum diets; whereas, there was a 'convex response' in red sorghum diets. Thus, at the intermediate 80°C conditioning temperature, starch digestion rates were at a minimum value for white, but at a maximum value for red sorghum-based diets, which is consistent with the significant sorghum type×temperature interaction (p

Seven sorghum-based broiler diets containing the reducing agent, sodium metabisulphite (SMBS) at levels of 0, 1.50, 2.25, 3.00, 3.75, 4.50 and 5.25 g/kg were prepared. The in vitro starch pasting properties of the sorghum-based diets and starch extracted from the diets were assessed by rapid viscosity analysis (RVA). The seven dietary treatments were offered to 294 male Ross 308 chicks from 10 to 24 days post-hatch to determine SMBS effects on starch and nitrogen digestion dynamics. Digesta samples were collected, freeze-dried and weighed for determination of digestibility coefficients and mean retention times in the proximal jejunum, distal jejunum, proximal ileum and distal ileum. The digestion kinetics of starch and nitrogen (N) were determined using an exponential mathematical model to relate digestibility coefficients to mean retention times in each small intestinal segment. SMBS inclusions linearly reduced apparent starch digestibility coefficients in the proximal jejunum (r = −0.444, P

Seven sorghum-based diets containing 0, 1.50, 2.25, 3.00, 3.75, 4.50 and 5.25 g/kg of the reducing agent sodium metabisulphite (SMBS) were prepared in which sodium levels were balanced with sodium bicarbonate. A red sorghum (766.4 g/kg starch, 78.6 g/kg protein) was hammer-milled through a 3.2 mm screen prior to being mixed into complete broiler diets containing 195 g/kg protein with an energy density12.97 MJ/kg, which were steam-pelleted at an 84 °C conditioning temperature. Each of the seven dietary treatments was offered to a total of 294 male Ross 308 chicks in seven replicate cages (6 birds per cage) from 10 to 24 days post-hatch to determine the effects of SMBS on growth performance, nutrient utilisation and nitrogen (N) digestibility coefficients in four small intestinal segments. SMBS did not linearly influence (P > 0.50) weight gains and feed intakes. However, SMBS quadratically improved (r = 0.416; P

To investigate the influence of exogenous phytase inclusions in poultry diets on the post-enteral availability of amino acids, wheat-soybean meal diets containing 0, 500, 1000 and 2000 phytase units (FTU)/kg were offered to eight replicate cages (six birds per cage) or a total of 192 male Ross 308 chicks from 7 to 28 days post-hatch. The parameters determined included growth performance, nutrient utilisation, bone mineralization, parameters of gizzard functionality, apparent ileal digestibility coefficients and disappearance rates (g/bird/day) of amino acids, plus concentrations of amino acids, glucose and ammonia in plasma from the portal circulation (anterior mesenteric vein). The inclusion of 500 FTU/kg significantly improved weight gain by 8.39% (1485 versus 1370 g/bird) and feed conversion ratio (FCR) by 5.10% (1.397 versus 1.472 g/g) in comparison to the control. Phytase inclusions significantly increased gizzard pH but not toe ash. The 2000 FTU/kg phytase inclusion significantly increased digestibility of 15 from 16 amino acids by an average of 5.29% (0.716 versus 0.680) and significantly increased apparent metabolisable energy (AME) by 0.45 MJ (12.43 versus 12.88 MJ) and N-corrected AME (AMEn) by 0.45 MJ (11.43 versus 11.88 MJ) relative to the control. The 500 FTU/kg phytase inclusion significantly increased free concentrations of seven amino acids (isoleucine, leucine, lysine, phenylalanine, tryptophan, valine and serine) in plasma from the anterior mesenteric vein based on pairwise comparisons and numerically increased concentrations of a further six amino acids. Phytase inclusions linearly reduced concentrations of glutamic acid and glutamine in the portal circulation, and there was a logarithmic relationship between phytase inclusions and increased plasma glucose concentrations. Reductions in the ratio of glutamate plus glutamine to glucose concentrations in portal plasma were significantly related to improvements in FCR. The outcomes of this study indicate that phytase can positively influence the post-enteral availability of amino acids. The inference is that phytase is manipulating the metabolic fates of amino acids and glucose in the gut mucosa and consideration is given to the possible responsible mechanisms for the observed outcomes.

The present study was conducted to evaluate the responses of growth performance and carcass traits in Cobb MV × 500 fast feathering broiler chickens fed maize, soybean meal (SBM) and peanut meal based diets containing different levels of digestible (dig) lysine (Lys). Dietary treatments consisted of 6 concentrations of dig Lys that ranged from 8.4 to 12.9 g/kg in increments of 0.9 g/kg. Two control diets with the medium level of dig Lys concentration of 11.1 g/kg were included where the positive control (PC) diet was a typical commercial diet based on maize and SBM and the negative control (NC) diet replaced part of SBM with100 g/kg peanut meal to allow higher supplementations of feed grade amino acids. Each of the eight experimental diets were offered to either male or female broiler chickens to form 16 experimental treatments and each treatment included 6 floor pens with 12 birds per pen. Broiler chickens were offered experimental diets from 14 to 35 days post-hatch. All diets were balanced with essential amino acids (EAA) by using ideal protein ratio approach and were offered to broiler chickens from 14 to 35 days post-hatch. Predictably, male broiler chickens had better weight gain (WG), feed intake (FI), feed conversion ratio (FCR) and breast meat yield (P

The preliminary assessment was designed to determine appropriate inclusion levels of the reducing agent, sodium metabisulphite (SMBS), in ‘all-sorghum’ broiler diets. Dietary SMBS inclusion levels of 0, 1.25, 2.5, 5.0, 7.5, 10.0, 12.5 and 15.0 g kg−1 were investigated with corresponding reductions (923–908 g kg−1) in dietary sorghum concentrations. In vitro evaluations included the determination of concentrations of free sulphydryl groups and disulphide bonds in all-sorghum diets. In vivo parameters included growth performance (14–21 days post-hatch), nutrient utilisation and apparent nitrogen (N) digestibility coefficients in four small intestinal sites in broilers at 21 days post-hatch. In addition, the effect of 5.0 g kg−1 SMBS on starch digestibility coefficients and sites of starch disappearance along the small intestine were determined. The reducing agent significantly increased free sulphydryl group and decreased disulphide bond concentrations. SMBS significantly depressed feed intakes at 5.0 g kg−1 and at higher inclusion levels and there was a linear reduction in feed intakes (r = −0.783; P 0.60) and proximal ileum (P>0.55). At 5.0 g kg−1, SMBS increased starch digestibility coefficients by 3.76% in the proximal ileum (0.966 versus 0.931; P

Two experiments were conducted to examine the influence of sorghum variety and the hydrothermal component of steam-pelleting diets on apparent amino acid digestibility coefficients and digestion kinetics of amino acids, nitrogen and starch in broiler chickens. In experiment one, 84 male Ross 308 chicks were offered steam-pelleted diets based on white (Liberty) and red (Buster) sorghum from 7 to 28 days post-hatch. In experiment two, the same red sorghum-based diets were offered to chicks from 7 to 28 days post-hatch as either unprocessed raw mash or reground mash following steam-pelleting at 95 °C. In both experiments, digesta samples from proximal jejunum, distal jejunum, proximal ileum and distal ileum were collected in their entirety at day 28. The samples were then freeze-dried and weighed for determination of mean retention time in each small intestinal segment. The digestion kinetics of amino acids, nitrogen and starch were determined using an exponential mathematical model to relate apparent digestibility coefficients with mean retention times in each small intestinal segment. In experiment one, white sorghum-based diets had significantly higher average amino acid digestibility coefficients than red sorghum in the proximal ileum and distal ileum (P r = −0.840, P

The influence of conditioning temperatures on apparent digestibility coefficients of amino acids at proximal jejunum, distal jejunum, proximal ileum and distal ileum were investigated in this study. Broilers were fed sorghum-based diets steam-pelleted at three conditioning temperatures (65, 80, 95 °C) from 7 to 28 days post-hatch. Digesta samples were collected at day 28 and freeze-dried and weighed for determination of amino acid digestibilities and mean retention time in each small intestinal segment. The digestion kinetics of amino acids were determined using an exponential mathematical model to relate digestion coefficients with mean retention times in each small intestinal segment. Increasing conditioning temperatures from 65 to 95 °C significantly increased apparent digestibility coefficients of phenylalanine at proximal jejunum, apparent digestibility coefficients of aspartic acid and proline at proximal ileum and apparent digestibility coefficients of arginine, lysine, aspartic acid and glycine at distal ileum. Conditioning temperatures linearly increased retention times in the distal ileum (P

a b s t r a c t Apparent amino acid digestibility coefficients in the proximal jejunum, distal jejunum, proximal ileum and distal ileum of broilers fed sorghum-based diets without or with exoge- nous protease were determined at 28 days post-hatch. The digestion kinetics of amino acids were determined using an exponential mathematical model to relate digestion coefficients at four intestinal sites with mean retention times in each small intestinal segment. Pro- tease increased average digestibility coefficients in the distal jejunum by 12.6% (0.681 vs. 0.605; P