Facilitating the acceptance of tangibly reduced-crude protein diets for chicken-meat production

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.

Protein digestive dynamics of meat and bone meals in broiler chickens

This study determined the variations in protein digestibilities and digestion rates in broiler chickens offered diets containing 7 different meat and bone meals (MBM). A total of 252 male Ross 308 broiler chickens were offered 7 atypical diets largely based on maize and MBM from 24 to 28 d post-hatch. Each experimental diet was offered to 6 replicates with 6 birds per replicate cage. Excreta were collected in their entirety from 25 to 27 d post-hatch and on 28 d post-hatch. Digesta samples were collected from the proximal jejunum, distal jejunum, proximal ileum and distal ileum. Apparent digestibilities of protein were determined in each segment and apparent digestibilities of amino acids were measured in the distal ileum. There were significant differences in apparent protein digestibility coefficients in the proximal jejunum (P = 0.006), where broiler chickens offered the high ash beef meal (diet 7) generated the lowest protein digestibility in the proximal jejunum (0.318). Similarly, there were significant differences in apparent digestibility coefficients in the distal jejunum (P < 0.001) and distal ileum (P < 0.001) but not in the proximal ileum. More pronounced differences were found in the disappearance rate of protein and there were significant differences in all 4 segments of the small intestine (P < 0.001). Broiler chickens offered the high ash beef meal had the lowest protein disappearance rate (P < 0.001). No difference was observed in the predicted protein digestion rate (P = 0.486) but chickens offered the high ash beef meal had the lowest potential digestible protein (0.662, P = 0.034) whereas the highest potential digestible protein (0.739) was detected in diet 5 (containing a beef meal). This study contributed to the establishment of a preliminary database to include digestion rates of starch and protein into practical diet formulation.

Synthetic and Crystalline Amino Acids: Alternatives to Soybean Meal in Chicken-Meat Production

: 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.

Capping dietary starch:protein ratios in moderately reduced crude protein, wheat-based diets showed promise but further reductions generated inferior growth performance in broiler chickens

The hypothesis that capping dietary starch:protein ratios would enhance the performance of broiler chickens offered reduced-crude protein (CP) diets was tested in this experiment. A total of 432 off-sex, male Ross 308 chicks were allocated to 7 dietary treatments from 7 to 35 d post-hatch. The experimental design consisted of a 3 × 2 factorial array of treatments with the seventh treatment serving as a positive control. Three levels of dietary CP (197.5, 180.0 and 162.5 g/kg) with either uncapped or capped dietary starch:protein ratios constituted the factorial array of treatments, whilst the positive control diet contained 215.0 g/kg CP. The positive control diet had an analysed dietary starch:protein ratio of 1.50 as opposed to a ratio of 1.68 in the uncapped 197.5 g/kg CP diet and 1.41 in the corresponding capped diet and the capped 197.5 g/kg CP diet displayed promise. The growth performance this diet matched the positive control but outperformed the uncapped 197.5 g/kg CP diet by 10.4% (2,161 vs. 1,958; P = 0.009) in weight gain, by 3.10% (3,492 vs. 3,387; P = 0.019) in feed intake on the basis of pair-wise comparisons and numerically improved FCR by 4.04% (1.616 vs. 1.684). However, the growth performance of birds offered the 180.0 and 162.5 g/kg CP dietary treatments was remarkably inferior, irrespective of dietary starch:protein ratios. This inferior growth performance was associated with poor feathering and even feather-pecking and significant linear relationships between feather scores and parameters of growth performance were observed. The amino acid profile of feathers was determined where cysteine, glutamic acid, glycine, proline and serine were dominant in a crude protein content of 931 g/kg. Presumably, the feathering issues observed were manifestations of amino acid inadequacies or imbalances in the more reduced-CP diets and consideration is given to the implications of these outcomes.

Potential of CIELAB colour scores to gauge the quality of sorghum as a feed grain for chicken-meat production

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.

Composition and characterisation of kafirin, the dominant protein fraction in grain sorghum

Context Sorghum is an important feed grain for chicken-meat production in Australia. However, it is usually considered inferior to wheat – the foremost feed grain. Kafirin, the dominant protein fraction in sorghum, may be a major contributor to this inferiority due to its negative influence on starch digestion and energy utilisation. Aims The objective of this study was to determine kafirin concentrations in sorghum relative to crude protein and amino acid profiles of both kafirin and total sorghum protein. Methods Concentrations of amino acids and kafirin in 19 Premium Grains for Livestock Program sorghum varieties were quantified. These data were combined with that of up to 14 Poultry Research Foundation sorghum varieties to generate the most exhaustive documentation of its kind. The methodology developed to quantify kafirin concentrations in sorghum is thoroughly described. In addition, essential amino acid profiles in 25 grain sorghums from Australian surveys completed in 1998, 2009 and 2016 were compared statistically. Also, consideration was given to relevant near-infrared spectroscopy predicted data from 992 sorghum varieties from 2014 to 2019. Key results The average kafirin concentration of 48.2 g/kg represented 51.9% of the 92.9 g/kg crude protein (N × 5.81) content in 33 varieties grain sorghum. Kafirin holds a substantial 62.7% share of leucine as the concentration was 8.53 g/kg in kafirin as opposed 13.73 g/kg in total sorghum protein. The proposal was advanced that kafirin contents of local sorghum crops have increased during the past two decades from the 1998, 2009 and 2016 surveys of amino acid profiles in grain sorghum. Conclusions Kafirin concentrations in Australian sorghum crops may have increased over the past two decades, which may be having a negative impact on the performance of broiler chickens offered sorghum-based diets. Implications Breeding programs should be directed towards sorghums with lesser kafirin proportions of sorghum protein and/or modified kafirin protein bodies to enhance the nutritive value of sorghum as a feed grain for chicken-meat production.

Impacts of reduced-crude protein diets on key parameters in male broiler chickens offered maize-based diets

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.

Extending daily feed access intervals does not influence lysine HCl utilization but enhances amino acid digestibilities in broiler chickens

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; P < 0.025) and feed conversion ratios (1.351 vs. 1.382; P < 0.005). Extending feed access intervals increased weight gain (1,542 vs. 1,303 g/bird; P < 0.001) and feed intake (2,142 vs. 1,748 g/bird; P < 0.001) but compromised feed conversion ratios (1.390 vs. 1.342; P < 0.001). Extending feed access intervals increased (P < 0.001) 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; P < 0.001), which was linearly related (r = -0.834; P < 0.001) 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 (P > 0.35) 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.

Effects of reduced crude protein levels, dietary electrolyte balance, and energy density on the performance of broiler chickens offered maize-based diets with evaluations of starch, protein, and amino acid metabolism

The crude protein (CP) content of 4 iso-energetic, maize-based diets containing 11.00 g/kg digestible lysine was reduced in gradations from 200 to 156 g/kg with increasing inclusions of synthetic, or unbound, essential amino acids. A constant dietary electrolyte balance (DEB) of 230 mEq/kg was maintained, but a second 156 g/kg CP diet had a DEB of 120 mEq/kg, and energy densities of the 156 g/kg CP diet were reduced in the sixth and seventh treatments. Each of the 7 dietary treatments were offered to 7 replicate cages (6 birds/cage) or a total of 294 Ross 308 off-sex male broilers from 14 to 35 D posthatch. Reductions in CP from 200 to 156 g/kg did not influence weight gain but quadratically increased feed conversion ratio (FCR) and linearly increased relative abdominal fat-pad weights and feed intakes. The reduction in DEB did not influence growth performance but did adversely influence some amino acid digestibilities. Reducing energy density by 100 kcal/kg did not influence growth performance of birds offered the 156 g/kg CP diet but numerically reduced fat-pad weights. The transition from 200 to 156 g/kg CP diets generally enhanced jejunal and ileal amino acid digestibility coefficients but had diverse effects on free amino acid concentrations in systemic plasma with a remarkable 116% increase in threonine. Starch:protein disappearance rate ratios linearly increased in the jejunum and the ileum following the same transition, and these expanding ratios were related to heavier fat-pads and compromised FCR. This study indicates that reductions in dietary CP from 200 to 172 g/kg supported by inclusions of unbound essential amino acids do not compromise growth performance, but a further reduction to 156 g/kg CP significantly increased FCR. Both heavier relative fat-pad weights and inferior FCR were related to expanding starch:protein disappearance rate ratios, which suggests condensed dietary starch:protein ratios may advantage birds offered reduced CP diets.

The influence of phytase, pre-pellet cracked maize and dietary crude protein level on broiler performance via response surface methodology

Background

The reduction of crude protein levels in diets for broiler chickens may generate economic, environmental and flock welfare and health benefits; however, performance is usually compromised. Whole grain feeding and phytase may improve the utilization of reduced crude protein diets.

Results

The effects of pre-pellet cracked maize (0, 15% and 30%) and phytase (0, 750 and 1500 FTU/kg) in iso-energetic maize-soy diets with three levels of crude protein (22%, 19.5% and 17%) were evaluated via a Box-Behnken response surface design. Each of 13 dietary treatments were offered to 6 replicate cages (6 birds/cage) of male Ross 308 broiler chicks from 7 to 28 d post-hatch. Model prediction and response surface plots were generated from experimental data via polynomial regression in R and only significant coefficients were included and discussed in the predicted models. Weight gain, feed intake and FCR were all influenced by pre-pellet cracked maize, phytase and crude protein level, where crude protein level had the greatest influence. Consequently, the reduction from 22% to 17% dietary crude protein in non-supplemented diets reduced weight gain, feed intake, relative gizzard weight, relative gizzard content and relative pancreas weight but improved FCR. However, the inclusion of 30% cracked maize to 17% crude protein diets restored gizzard weight and 1500 FTU phytase inclusion to 17% crude protein diets increased relative gizzard contents and pancreas weights. Cracked maize and phytase inclusion in tandem to 17% crude protein diets increased weight gain, feed intake and FCR; however, this FCR was still more efficient than broilers offered the non-supplemented 22% crude protein diet. Broilers offered the pre-pellet cracked maize and phytase inclusions reduced AME in 22% crude protein diets but improved AME by 2.92 MJ (14.16 versus 11.24 MJ; P < 0.001) in diets containing 17% crude protein. Ileal N digestibility was greater in broilers offered diets with 17% crude protein than those offered the 22% crude protein diet; irrespective of phytase and pre-pellet cracked maize.

Conclusion

Pre-pellet cracked maize and phytase inclusions will improve the performance of broilers offered reduced crude protein diets.

The ranked importance of dietary factors influencing the performance of broiler chickens offered phytase-supplemented diets by the Plackett-Burman screening design

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 < 0.001) and gain:feed by 9.36% (P < 0.001). Increasing calcium levels reduced weight gain by 6.36% (P < 0.001) and gain:feed by 2.60% (P < 0.001). The high calcium level increased gizzard pH from 2.78 to 3.01 (P < 0.005). Whole barley significantly increased relative gizzard weights and contents, pancreas weights and both ileal N digestibility coefficients (0.774 versus 0.803; P < 0.001) and ileal N disappearance rates (23. 3 versus 24.5 g/bird/day; P < 0.001). 4. Overall, digestible lysine level and calcium level were identified as the most influential dietary factors to influence growth performance of broilers offered phytase-supplemented diets, which hold implications for practical diet formulations.

Influence of starch sources and dietary protein levels on intestinal functionality and intestinal mucosal amino acids catabolism in broiler chickens

Background

There is growing interest in carbohydrate and protein nutrition to enhance the efficiency of animal production. Reduced-crude protein diets depress environmental pollution and feeding cost, but the challenge to their adoption is maintaining digestive function and growth performance of birds. The present study was conducted to evaluate the influence of different dietary starch sources and protein levels on intestinal functionality and mucosal amino acid catabolism.

Methods

Six dietary treatments, based on maize and soybean meal, were offered to 360 AA⁺ male chicks from 6 to 35 d post-hatch as a 3 × 2 factorial array. Either waxy rice or amylose was added to a conventional maize-soy diet to provide three sources of starch with different digestion rates and relatively high and low dietary protein levels. Growth performance, parameters of intestinal functionality and concentrations of free amino acid in the portal circulation were determined.

Results

In the grower phase, starch source influenced (P < 0.02) weight gain as diets containing amylose supported significantly higher weight gains than waxy rice. Significant increase of ileal ATP concentrations and Na⁺/K⁺-ATPase activity were found in amylose treatment. Also, amylose decreased BrdU positive cell numbers and down-regulated mRNA expression for CASP-3. GOT activity in the ileum was higher (P < 0.01) in birds offered low protein diets and there was a trend (P = 0.057) for waxy rice as a starch source to increase ileal GOT activities. There was a significant influence on the concentration of seventeen amino acids in the portal circulation with tryptophan the one exception. Waxy rice as a starch source generated 13.6% and 22.4% numerically higher concentrations of non-essential amino acids than maize and amylose, respectively.

Conclusions

Amino acid catabolism in the gut mucosa is subject to nutritional regulation. Given that amino acids can be spared from catabolism in the gut mucosa by supplementation of amylose, it follows their post-enteral availability would be improved and intestinal energy would be derived more efficiently from glucose.

Box-Behnken optimisation of growth performance, plasma metabolites and carcass traits as influenced by dietary energy, amino acid and starch to lipid ratios in broiler chickens

A Box-Behnken designed study was completed to predict growth performance, carcass characteristics and plasma hormone and metabolite levels as influenced by dietary energy, amino acid densities and starch to lipid ratios in male broiler chickens. The design comprised three dietary energy densities (11.25, 12.375 and 13.5 MJ/kg), three digestible lysine concentrations (9.2, 10.65 and 12.1 g/kg) and three starch to lipid ratios (4.5, 12.25 and 20.0) in broiler diets based on maize and soybean meal. Each of thirteen dietary treatments was offered to 10 replicates of 15 birds per replicate floor pen or a total of 1,950 Ross 308 male broiler chickens from 21 to 35 days post-hatch. Increasing dietary energy decreased feed intake with a quadratic relationship between feed intake and dietary standardised ileal digestible (SID) Lys concentrations, where increasing SID Lys initially increased and then depressed feed intake. Increasing dietary amino acid density increased body weight gain and carcass weight; however, dietary energy did not influence body weight gain, carcass and breast meat weight. Feed efficiency was positively influenced by energy and amino acid densities but negatively influenced by starch to lipid ratios and energy and amino acids had more pronounced impacts than starch to lipid ratios. This study indicated that both energy and amino acid densities regulate feed intakes in broiler chickens. Body weight gain of modern broiler chickens is more responsive to amino acid densities; nevertheless, dietary energy density continues to play an important role in protein utilisation, as reflected in significantly reduced plasma uric acid levels.

Feeding whole grain and phytase to meat chickens: recent Australian experience

Both whole-grain feeding and exogenous phytases have been widely accepted by the chicken-meat industry, so any interactions that arise from this combined supplementation are potentially important. Nevertheless, there is a paucity of research evaluating the effect of phytase under whole-grain feeding regimens. Whole-grain feeding increases relative gizzard weights and gizzard functionality. However, the gizzard is the primary site of phytate degradation by phytase, so this combined supplementation should enhance phytase efficacy. Moreover, there has been recent progress towards understanding the influence of whole-grain feeding and exogenous phytase on broiler performance, which is discussed. Further research is warranted to establish a whole-grain feeding regimen that generates robust gizzard responses so as to enhance feed efficiency, energy utilisation and phytase efficacy.

Dietary starch to lipid ratios influence growth performance, nutrient utilisation and carcass traits in broiler chickens offered diets with different energy densities

Twelve experimental diets with three levels of energy densities (11.25, 12.38 and 13.50 MJ/kg) and fours levels of starch to lipid ratios (14:1, 12:1, 7:1, 4:1) were offered to 288 male Ross 308 broiler chickens. All the diets were formulated to contain consistent digestible lysine to metabolisable energy ratios (0.87 g digestible lysine/MJ AMEn) and ideal amino acid ratios. Growth performance was monitored from 7 to 27 days post-hatch and parameters of nutrient utilisation (AME, AMEn, AME:GE ratios, N retention) were determined from 24 to 26 days post-hatch. Apparent protein (N) and starch digestibility coefficients, carcass yield and composition were determined at 27 days post-hatch. There were no interactions between energy densities and starch to lipid ratios on growth performance and carcass weights (P > 0.05). Feed intake was reduced with increased energy densities (P < 0.001). Weight gain and FCR were improved with increased dietary energy densities (P < 0.0001). Starch to lipid ratios linearly increased weight gain (r = 0.448, P = 0.001) and feed intake (r = 0.509, P < 0.001) without influencing FCR (P > 0.75). Both nutrient densities and starch to lipid ratios significantly impacted on carcass weight and yield. Heavier carcass weights and higher yields were observed in broiler chickens offered diets with high nutrient density (P ≤ 0.001). Carcass weight (r = 0.441, P < 0.005) was positively correlated with starch to lipid ratios and this tended to be the case for carcass yield (r = 0.277, P = 0.057) too. However, there were interactions on lipid concentrations in carcass (P < 0.001) as broiler chickens offered diet containing the lowest nutrient density and the highest starch to lipid ratio had the highest lipid carcass concentration of 12.94%. In conclusion, protein and energy need to be considered in tandem in practical diet formulation, especially in diets containing high crystalline amino acid inclusions. The impact of lipid on feed intake and starch on carcass lipid concentrations should also be taken into consideration.

Outlook: Sorghum as a feed grain for Australian chicken-meat production

This review is an outlook for sorghum as a feed grain for broiler chickens based on a survey of relevant stake-holders and recent research outcomes. Australian grain sorghum production will probably continue to generate a harvest in the order of 2.5 × 106 t of which some 7.9 × 105 t will be used as a feed grain for poultry and pigs. Feed grains are included primarily to provide energy from starch, but energy utilisation by broiler chickens offered sorghum-based diets is relatively inferior, because of incomplete starch digestion. Kafirin, the dominant protein fraction, 'non-tannin' phenolic compounds and phytate are 3 'starch extrinsic' factors in sorghum that compromise starch digestibility and energy utilisation in broiler chickens offered sorghum-based diets. Kafirin concentrations in 6 sorghum varieties were negatively correlated with metabolizable energy to gross energy (ME:GE) ratios (r = -0.891; P < 0.02) or the efficiency of energy utilisation in broiler chickens. Importantly, kafirin proportions of sorghum protein may be increasing with time in Australia. If so, this represents a fundamental challenge to sorghum breeders which presumably could be met by the development of sorghum varieties with different characteristics, especially in relation to the γ- and β-kafirin fractions. White sorghum varieties contain lower polyphenol concentrations which should be advantageous as concentrations of total phenolic compounds were negatively correlated to ME:GE ratios (r = -0.838; P < 0.04) in 6 sorghum varieties. It would be desirable if more white varieties were to become available. It is suggested that responses to exogenous phytase in birds offered sorghum-based diets would be more robust if sorghum were to contain lower concentrations of kafirin and phenolic compounds. Paradoxically, while better sorghum varieties almost certainly could be developed, it may not necessarily follow that they will command a price premium from poultry and pig producers.

Progress in comprehending the phytate–phytase axis in chicken-meat production

After an extended delay, the level of acceptance of exogenous phytases by the global chicken-meat industry is now almost complete. Contemporary bacterial phytases degrade phytate primarily in the gizzard. The extent of phytate degradation determines the extent to which phytate-bound phosphorus (P) is liberated; however, studies designed to investigate phytate degradation along the digestive tract have generated some confusing outcomes. This may be related to the reactivity of the phytate moiety, coupled with problems with inert dietary markers and perhaps a lack of complete and uniform extractions of phytate from digesta due to variations in digesta pH and phytate solubility. Quite recently, phytase was shown to have profound impacts on sodium (Na) digestibility coefficients in four segments of the small intestine. This has obvious implications for intestinal uptakes of glucose and amino acids via their respective Na+-dependent transport systems and it is possible that phytate and phytase have reciprocal impacts on ‘sodium pump’ (Na+, K+-ATPase) activity. It has been recently demonstrated unequivocally that phytase has the capacity to increase amino acid digestibility coefficients to the extent that phytase may generate a ‘proximal shift’ in the sites of amino acid absorption. The impact of phytase on starch digestibility is more equivocal and phytase responses may stem more from enhanced glucose absorption rather than starch digestion. The acceptance of phytase is hardly surprising, given its capacity to increase P utilisation coupled with numerous other positive influences that are still being properly realised.

Rapid protein disappearance rates along the small intestine advantage poultry performance and influence the post-enteral availability of amino acids

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.

Inclusion levels and modes of whole grain incorporation into wheat-based rations differentially influence the performance of broiler chickens

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 < 0.05) feed intakes while the 30% post-pellet separated treatment improved (P < 0.01) feed conversion ratios (FCR). WGF regimes significantly increased relative gizzard weights. 4. Overall, WGF generated profound responses in AME, ME:GE ratios, N retention and AMEn that were highly correlated with relative gizzard weights. In general, WGF improved starch and protein (N) digestibilities and again there were some correlations with these outcomes and relative gizzard weights. 5. Post-pellet WG inclusions where WG and pelleted concentrate were offered separately provided chickens with the opportunity to choice feed. Birds showed a preference for the relatively high-protein pelleted concentrate and at 30% WG, this resulted in an improvement in FCR of 7.69% (1.260 versus 1.365; P < 0.001) relative to the ground-grain control diet.