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Item Development of an assay for the determination of dietary apparent ileal nitrogen and amino acid digestibilities in the meat chicken : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University(Massey University, 1991) Yap, Kee HorBiological procedures which quantify protein value are expected to beneficially influence efficiency of nutrient provision in dietary formulations for the livestock, industry. This thesis provides a review of two widely employed quantitative assessments, "Digestibility" and "Availability" and in the experimental section describes a series of experiments undertaken on meat chicken to refine assay procedures involved in the determination of protein and amino acid apparent ileal digestibility values. Five experiments were undertaken. (1a) A comparison of two feeding procedures with three diets differing in particle size with a view to evaluating the effect of feeding behaviour on the final composition of the test diet in the crop. (1b) Determination of crop residue composition associated with time following feeding with two feeding procedures and two diets differing in particle size. (2) A comparison of the effects of two slaughter procedures and two flushing solutions on ileal N digestibility of meat and bone meal. (3) A comparison of the effect of time of slaughter following feeding on ileal N values of two diets. (4) Determination of the effect of length of ileum on ileal N digestibility values of two diets. (5) Determination of the effect of age on ileal N and AA digestibilities of two diets. In 1a there was clear evidence that bird eating behaviour and particle size of the test diet influenced crop content proportions of a number of criteria, more notably chromium and nitrogen. For coarse particle diets an intubation feeding procedure produced a closer match of material in the crop with that of the untouched diet than a free access provision of food procedure. In 1b the results of the study were inconclusive and no satisfactory cause for inconsistencies that developed between treatments could be found. In 2, two slaughter procedures, euthanasia by sodium pentobarbitone and asphyxiation by carbon dioxide, resulted in significantly different (P<0.05) apparent ileal nitrogen (N) digestibility. Differences between flushing solutions, distilled water and physiological saline were small and not significant (P<0.05). In 3, for two diet types, N and dry matter (DM) digestibilities were relatively constant over sampling times of 2 to 5 hours following the start of feeding. Ileal digesta sampled quantities tended to be greatest at the 4 hour sampling interval. In 4, differences in N and DM digestibilities of digesta samples drawn from sections of the ileum up to 30 cm in length as measured from the ileo-caecal junction were generally small and non significant. In 5, bird age had no significant effect on N and DM digestibilities. The main conclusions drawn were that intubation better retained the integrity of food reaching the crop. Sodium pentobarbitone was a preferable method of slaughter. Ileal length sampled needed to be kept as short as consistant with providing adequate sample material and largest sample sizes were obtainable around 4 hours following the start of feeding.Item An economic analysis of least-cost layer rations : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Farm Management at Massey University(Massey University, 1974) Ryan, Oliver PatrickFifteen treatments, replicated once, each containing eighty four birds of three strains of White Leghorn layers (White Base a, White Base b, M. Line) were fed rations ad libitum of five different metabolisable energy levels (2315, 2535, 2756, 2976, 3197 k. cal. M.E. per kg.) and three different protein levels (16, 17, 18 gms. per hen per day, based on an energy intake of 305 k. cals. per hen per day) to obtain quantitative estimates of the physical input/output relationships of layer production. Three other treatments, plus a control, were fed to obtain data on the response of laying hens to restricted energy intake and improved protein quality. All rations were formulated to least cost using Linear Programming. Least Squares multiple regression was used to obtain linear response functions for feed intake, egg number, egg weight and liveweight gain (the variables included in a net revenue function for layers under New Zealand production conditions). Feed intake was expressed in terms of dietary energy concentration and initial liveweight. Statistical problems encountered dictated that predicted nutrient intakes were used as the independent variables in the estimation of the egg number and liveweight gain functions. Predicted energy intake and methionine intake accounted for differences in egg number, particularly for White Base b layers. Predicted energy intake, methionine intake and isoleucine intake accounted for differences in liveweight gain. There were no significant differences between average egg weights. There were significant strain differences in ad libitum feed consumption, egg number, average egg weight and liveweight gain. A net revenue function was estimated in terms of the endogenous variables (dietary nutrient concentrations) which were included in the layer response functions. This was analysed in terms of the endogenous variables for the then current egg and feed prices.Item The nutritional value of ryegrass-white clover leaf protein concentrate : a thesis presented in partial fulfillment [sic] of the requirements for the degree of Doctor Philosophy in Biochemistry at Massey University(Massey University, 1983) Johns, David CarvilleLeaf Protein Concentrate (LPC ) , which was manufactured from a mixture of Ryegrass and White Clover (Lolium perenne and Trifolium repens) at the Ruakura Agricultural Research Centre , was evaluated as a possible protein source for feeding to chickens . The nutritional value of LPC was compared to that of soybean meal ( SBM ) . LPC was shown to have a lower nutritional value than SBM in the growth trials . The addition of methionine or cystine to the diet containing LPC improved both food utilization and weight gain of the chickens . These growth parameters showed the greatest improvement when 2 g methionine/kg diet was added to the LPC diet. The additional quantity of 2g methionine/kg diet was similar to the amount of sulphur amino acid contributed by LPC to the d i e t ; 1.8 g sulphur amino acid from L PC /kg diet. When an equivalent amount of cystine (1.6g) to methionine , on a sulphur basis , was added to the LPC d i e t and fed to chickens , it was shown to support the same amount of growth and maintain a similar food utilisation level as additional methionine . LPC contributed only 0.6g cystine/kg of diet . As this was much lower than the added cystine and/or methionine , it was concluded that the availability of cystine in the whole diet was reduced by the presence of LPC rather than the lack of availability of cystine in LPC alone . The following information was also obtained : - (i) Pancreatic hypertrophy and increased pancreatic enzyme activity (trypsin and chymotrypsin ) occurred due to feeding the LPC diet . (ii) The invitro exhaustive enzyme digestibility study indicated that while the overall digestibility of LPC was approximately 6% lower than that of SBM, none of the individual amino acid digestibility estimates i n LPC diverged markedly from the mean . All LPC amino ac ids were released equally by enzyme hydrolysis . (iii) In contrast to the invitro findings , the in vivo mean amino acid availability estimates for the ingredient LPC (as measured in the excreta) were lower than the corresponding SBM estimates by approximately 1 5% . The cystine availability estimate for the ingredient LPC was only 5 1 . 2% in terms of corrected amino acid availability ( CAAA), and 1 1 . 9% in terms of apparent amino acid availability ( ApAAA). By comparison the cystine availability estimates for the ingredient SBM were 80 . 8% CAAA and 7 5 . 7 % ApAAA. When the diets containing LPC or SBM were assayed by the same technique , the differences in the amino acid availability estimates were markedly reduced . The availability estimates of cystine in the LPC diet were still lower than the other amino acid availability estimates for the LPC diet . These however were only 8-10% lower than the corresponding estimates for the SBM diet. (iv) The mean amino acid digestibility estimates, derived by analysis of the ileal contents of chickens fed with the LPC d i e t were 26% lower than those for chickens fed the SBM d i e t s . The cystine digestibility estimates for the LPC d i e t was approximately 45% lower than the corresponding cystine digestibility estimate for the SBM diet. These results indicated that digestion and/or absorption of the LPC diet was probably being retarded as compared with the SBM diet. (v) Supplementation of the LPC diet with the antibiotic , Neomix , gave an improvement in growth and an increase in the mean amino acid availability ( measured by excreta analysis ) of approximately 7%. This indicated that the gut microflora were influencing the nutritional value of LPC . Feeding the LPC diet in comparison to feeding the SBM diet also tended to increase the level of c1 9 cyclopropane fatty acid in the excreta. This indicated that feeding the LPC diet was influencing the nature and/or activity of the microfloral population . The physiological and metabolic effects of feeding r aw soybean meal and/or trypsin inhibitors , which have been reported in the literature, included pancreatic hypertrophy , increased pancreatic proteolytic enzyme activity , retardation of ileal protein digestibility and.an influence by gut microflora . Each of these factors were characteristic of chickens fed the 1PC diet. It was therefore concluded that the additional need for cystine or methionine by chickens fed the 1PC diet , was due to the presence of trypsin inhibitors in the 1PC . It was demonstrated, by feeding 1 - (methyl 14c) methionine that phenolic compounds were being methylated . However the need for detoxification of aromatic compounds , which required methionine (as a methyl donor ) and /or arginine ( ornithine ) , could not explain the growth depression experienced by chickens fed the unsupplemented 1PC diet. The feeding of 1- (methyl 14c) methionine in conjunction with the 1PC diet also indicated that the digestibility of methionine was not being hindered during the digestive process by preferential binding with other compounds in the 1PC diet. I t was concluded from the result s of this study that 1PC adequately supplemented with methionine , could b e a useful addition to the range of ingredients available for use in poultry feeds.Item Influence of feed processing on the performance, nutrient utilisation and gut development of poultry and feed quality : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Poultry Nutrition at Massey University, Palmerston North, New Zealand(Massey University, 2011) Abdollahi, Mohammad Reza; Abdollahi, Mohammad RezaThe first two experiments of this thesis investigated the effects of conditioning temperature in relation to grain type (maize, wheat and sorghum) on the performance, nutrient utilisation and digestive tract development of broiler starters. The third experiment examined the influence of feed form (mash vs. pellet) and conditioning temperature in broiler starters fed wheat-based diets. The effects of improved pellet quality from the addition of a pellet binder or/and moisture to a wheat-based diet, and the effects of pellet diameter and pellet length on the quality of pellets and, performance, nutrient utilisation and digestive tract development of broilers were studied in fourth and fifth experiments, respectively. In the first experiment discussed in Chapter 4, increasing conditioning temperatures decreased the weight gain and feed intake of broilers fed wheat-based diets, whereas birds fed maize-based diets conditioned at 60 and 90 ºC had higher weight gain and feed intake than those fed the diet conditioned at 75 ºC. Increasing conditioning temperatures increased the feed per gain in both grain-type diets. Pellet durability index (PDI) improved with increasing conditioning temperatures in wheat-based diets, but was unaffected in maize-based diets. In wheat-based diets, increasing conditioning temperatures decreased the ileal digestibility of nitrogen (N) and starch. Ileal N digestibility of maize-based diets conditioned at 60 and 90 ºC was higher than at 75 ºC. Starch digestibility was unaffected by conditioning temperature in maize-based diets. No effect of conditioning temperature was found for the apparent metabolisable energy (AME). Data reported in Chapter 5 showed that birds fed maize- and sorghum-based diets conditioned at 60 ºC had a similar weight gain to those fed diets conditioned at 90 ºC and higher than those fed diets conditioned at 75 ºC. In both grain-type diets, birds fed diets conditioned at 60 and 90 ºC tended to have higher feed intake than those fed diets conditioned at 75 ºC. Conditioning temperature had no effect on the feed per gain. Increasing conditioning temperatures caused gradual improvements in the PDI of maize-based diets, while the improvement was marked in the sorghum-based diet conditioned at 90 ºC. In both grain-type diets, pellet hardness increased with increasing conditioning temperatures, particularly at 90 ºC. In maize-based diets, ileal N digestibility was poorer at 75 ºC compared with 60 and 90 ºC whereas ileal starch digestibility was unaffected by conditioning temperature and AME was higher at 75 ºC compared with 60 and 90 ºC. For sorghum-based diets, increasing conditioning temperatures resulted in linear reductions in the ileal N and starch digestibility and AME. Data reported in Chapter 6 showed that in mash diets, increasing conditioning temperatures above 60 ºC had negative effects on weight gain, feed per gain and nutrient utilisation of broiler starters. But the deterioration in performance parameters caused by conditioning at higher temperatures was restored when steam-conditioned mash diets were pelleted. Pellet durability and hardness increased with increasing conditioning temperatures. Data reported in Chapter 7 showed that the negative effect of higher conditioning temperature on weight gain, and to some extent feed intake, of broilers is not limited to the starter period (d 1 to 21), but can also be carried over the whole growth period (d 1 to 35). This study also illustrated possibilities for high quality pellets to be manufactured by the addition of pellet binder or/and moisture to a mash diet without the need for high conditioning temperatures. The final experiment (Chapter 8) demonstrated that increasing the pellet length from 3- to 6-mm during the grower period (d 10 to 21) positively influenced the weight gain and feed per gain of broilers. While the weight gain response disappeared as the birds grew older, improvements in feed per gain was maintained over the finisher (d 22 to 42) and whole grow-out (d 10 to 42) periods in 4.76-mm diameter pellets. This study also showed that using a small diameter die hole and longer pellet length may have an additive effect on pellet quality, and provide opportunities to produce high quality pellets under low conditioning temperatures. The major finding of this thesis research was that the balance between the negative effect of high conditioning temperatures on nutrient availability and the positive effect on pellet quality is relevant in determining the broiler performance. The probability and magnitude of these two counteracting effects determine the performance of broilers. Another important finding was that the pre-conditioning addition of moisture and the use of small diameter die hole and longer pellet length can effectively address pellet quality concerns at low conditioning temperatures.Item Feed enzymes and whole wheat in poultry diets : a thesis presented in partial fulfilment of the requirement for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand(Massey University, 2003) Wu, YubenSeven studies were undertaken to examine the effects of microbial phytase, glycanases, and whole wheat feeding in broiler diets. The major focus of this doctoral research was to investigate the effects of a microbial phytase produced by solid state fermentation in broiler diets. 1. The aim of the first study was to examine the effects of microbial phytase on the performance, apparent ileal digestibility of phosphorus (P), phytate P and nitrogen, and utilisation of nutrients in male and female broilers fed wheat-soy diets from 1 to 42 day of age. There were eight dietary treatments. Diets 1 to 4 were supplemented with inorganic phosphorus to contain 0.30, 0.36, 0.42 and 0.48% of non-phytate P (nP), respectively in the starter phase (1-21 day) and 0.20, 0.26, 0.32 and 0.48% in the finisher phase (22-42 day), respectively. Diets 5 to 8 were based on diet 1 and supplemented with phytase to contain 500, 1000, 1500 and 2000 PU/kg diet, respectively. Within sex, each of the eight dietary treatments was assigned to five pens of eight birds each. In both sexes, weight gain (P<0.05 to 0.001), feed efficiency (P<0.05 to 0.001) and toe ash contents (P<0.001) were increased as the P or phytase were added to low-P diet (diet 1). The magnitude of increments in performance and toe ash contents parameters were greatest with the first addition of P or phytase and then tended to plateau with further additions. Feed efficiency of birds fed phytase-supplemented diets was superior to those fed adequate-P diets. Toe ash contents of birds fed low-P diet with 500 PU/kg diet were comparable to those fed adequate-P diets. Addition of 500 PU/kg phytase to the low-P diet increased the nitrogen digestibility by 3.1 and 5.3% in males and females, respectively. Addition of phytase increased the apparent metabolisable energy (AME) of wheat-soy diets during the starter and Finisher phases, but the increments were greater in the finisher diets. Based on weight gain responses to graded additions of supplemental non-phytate P and phytase, estimates were obtained for P equivalency of the microbial phytase. These estimates translate into P release values of 72 to 131% from phytate and are apparently spurious. These unexpectedly high equivalency estimates may be due, partly, to the secondary enzymes activities present in the phytase product evaluated. 2. Selected data from the first study were analysed to compare the influence of sex on the performance, toe ash contents, phytate P release, AME and digestibility of nutrient in broilers fed diets containing low and adequate dietary levels of phosphorus. Sex of broilers had no effect on AME values determined during week 3. During week 6, the AME values for male broilers were higher (P<0.01) than those for the females. Female broilers tended (P<0.10) have a higher ileal nitrogen digestibility than the males. Apparent ileal phytate-P degradation values in males were higher than those in females (0.282 vs 0.234), but the differences were not significant (P>0.05). A significant interaction (P<0.05) between nP level x sex was observed for apparent ileal P digestibility. Increasing dietary nP levels increased apparent ileal P digestibility in both males and females, but the improvements were higher in females (13.4 vs 6.1 percentage units). 3. The aim of the second study was to examine the influence of microbial phytase addition on the performance, toe ash contents and nutrient utilisation of male broilers fed diets based on corn and wheat. The experiment was conducted as a 2 x 2 x 2 factorial arrangement of treatments. Within the factorial, two diet types (corn-soy or wheat-soy) containing two levels of non-phytate P (0.30 or 0.45%) were evaluated and each level of non-phytate P was supplemented with 0 or 500 PU phytase/kg diet. The results showed that microbial phytase was effective in both corn-based and wheat-based diets and that with supplemental 500 PU phytase/kg, dietary P level can be lowered by 0.15% to reduce excreta P output by 35% and still maintain comparable growth performance and bone mineralisation to birds fed a diet containing adequate levels of P. Phytase addition improved the AME values of wheat-based diets, but had little effect on the AME of corn-based diets. Phytase improved ileal nitrogen digestibility in both diet types, but the responses to added phytase tended to be higher in wheat-based diets, as shown by a diet type x phytase interaction (P<0.10). 4. The aim of the third study was to examine the influence of phytase and glycanases, individually or in combination, on the AME and nutrient digestibility of sorghum, corn, wheat and barley using 4-week-uld broilers. Microbial phytase improved (P<0.05) apparent ileal phosphorus digestibility in all cereals. Phytase supplementation improved (P<0.05) the AME of corn and barley, and numerically improved the AME in sorghum and wheat. Further improvements (P<0.05) in the AME of wheat and barley were observed when the phytase was combined with glycanases. The observed improvements in AME were not always associated with enhanced digestibility of protein and starch. 5. In the fourth experiment, potential beneficial effects from the side activities present in a microbial phytase produced by the solid state fermentation were examined by comparing the release of phosphorus, reducing sugars and α-amino nitrogen by two other phytase preparations in wheat- and corn-based diets using an in vitro digestion model. Microbial phytase produced by solid state fermentation released more (P<0.05) phytate-bound P (11.0% and 7.8% in wheat- and corn-based diets, respectively) and α-amino nitrogen (1.7% and 6.2% for wheat- and corn-based diets, respectively) than a phytase produced by submerged liquid fermentation without detectable side activities. Phytase produced by solid state fermentation also released 2.9% more reducing sugars in wheat-based diets and 6.2% α-amino nitrogen in corn-based diets. The superiority of microbial phytase produced by solid state fermentation in releasing nutrients in both types of diets is likely to be due to the presence of other enzyme activities. 6. In the fifth experiment, the influence of microbial phytase and xylanase, individually or in combination, on the performance, AME, digesta viscosity, digestive tract measurements and gut morphology in broilers fed wheat-soy diets containing adequate P levels were examined. The experimental diets were formulated by supplementing the basal diet with xylanase (1000 XU/kg), phytase (500 PU/kg) or combination of phytase and xylanase. The results showed that microbial phytase was as effective as xylanase in improving the performance of broilers. This may be due to the phytase product used in the study was produced by solid state fermentation and contained relatively high levels of β-glucanase, xylanase and protease. Supplemental phytase improved (P<0.05) the weight gains and feed efficiency by 17.5 and 2.9%, respectively. Corresponding improvements due to the addition of xylanase were 16.5 and 4.9%, respectively. Combination of phytase and xylanase had no further effects. The improved performance by supplemental phytase or xylanase was associated with reduced digesta viscosity, improved AME, and reduced relative weight and length of small intestine. Phytase and xylanase supplementation had no effect (P>0.05) on villus height, crypt depth, goblet cell number, epithelium thickness, and ratio of crypt depth to villus height in duodenum, jejunum and ileum. The only exception was that addition of phytase increased (P<0.05) villus height in the duodenum and decreased (P<0.05) the number of goblet cells in the jejunum compared to those in the unsupplemented basal diet. Interestingly, xylanase supplementation tended (P<0.10) to increase goblet cell numbers in the duodenum and decreased (P<0.05) crypt depth in the jejunum. 7. Whole grain feeding for broilers has received attention in recent years due to associated economic benefits. The aim of the sixth experiment was to examine the influence of method of whole wheat inclusion and xylanase supplementation on the performance, apparent metabolisable energy, digesta viscosity, and digestive tract measurements of broilers fed wheat-based diets. A 3 x 2 of factorial arrangement of treatments was used with three diet forms (64.8% ground wheat [GW], GW replaced with 20% of whole wheat before [WW1] or after cold-pelleting [WW2]) and two enzyme doses (0 and 1000 XU/kg diet). The results demonstrated the beneficial effects of whole wheat inclusion and xylanase supplementation in broiler diets. Birds fed diets containing whole wheat had improved (P<0.05 to 0.001) weight gain (2.1-3.9%), feed efficiency (4.1-5.8%) and AME (3.6-6.0%) compared to those fed diets containing ground wheat. The relative gizzard weights of birds fed WW2 diets were higher (P<0.05) than those fed GW and WW1 diets. Pre-pelleting inclusion of whole wheat had no effect (P>0.05) on the relative gizzard weights. Post-pelleting inclusion of whole wheat resulted in greater improvements (P<0.05 to 0.001) in feed efficiency, AME and relative gizzard weights compared to the pre-pelleting treatment. Improved performance with post-pelleting inclusion of whole wheat was probably due to the development of gizzard and to improved AME. However, it is difficult to propose a mechanism for the improvements observed with pre-pelleting inclusion of whole wheat. Improvements in bird performance by xylanase supplementation were associated with reduced digesta viscosity and improved AME. Neither xylanase supplementation nor whole wheat inclusion influenced (P>0.05) the relative weights and length of the duodenum, jejunum, ileum or total small intestine. 8. The aim of the seventh study was to examine the influence of post-pelleting inclusion of whole wheat and xylanase supplementation on the performance, digestive tract measurements and carcass characteristics of broilers fed wheat-soy diets from 1 to 35 days of age. There were five dietary treatments. Diet 1 was based on corn and soybean meal. Diets 2 and 3 were based on ground wheat (GW) and soybean meal without and with added xylanase at a level of 1000 XU/kg, respectively. Diets 4 and 5 were whole wheat (WW) replacing GW (10 and 20% whole wheat replacing GW during 1-21 and 22-35 day, respectively) without and with added xylanase at a level of 1000 XU/kg, respectively. Post-pelleting inclusion of whole wheat reduced (P<0.10) weight gains, but improved (P<0.05) the feed efficiency over the 35-day experimental period. Improved feed efficiency with whole wheat inclusion was associated with the development of gizzard. Xylanase supplementation improved the performance of broilers fed both ground wheat and whole wheat diets. Interestingly, feed efficiency of birds fed diets with whole wheat and supplemental xylanase were comparable to those fed corn-based diets. The 'apparent additivity of the combination of whole wheat and xylanase suggests that the mechanisms involved are different. Neither whole wheat inclusion nor xylanase supplementation influenced (P>0.05) the relative weight and length of the small intestine, carcass recovery and relative weights of breast muscle and abdominal fat pad.Item Feed particle size, whole wheat inclusion and xylanase supplementation in broiler diets : influence on the performance, digesta characteristics and digestive tract development : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Poultry Nutrition at Massey University, Palmerston North, New Zealand(Massey University, 2008) Amerah, Ahmed M.The first three experiments of this thesis examined the effects of particle size reduction of grains in relation to feed form (mash vs. pellet), grain type (wheat vs. maize) and xylanase supplementation on broiler performance, energy utilisation, digestive tract development and digesta parameters. The fourth experiment examined the interaction between wheat hardness and xylanase supplementation. The effects of insoluble fibre source and whole wheat inclusion were studied in the fifth experiment. In the first experiment (Chapter 4), pelleting reduced nitrogen-corrected apparent metabolisable energy (AMEn), but broiler performance was superior in birds fed pelleted wheat-based diets compared to those fed mash diets. Feed form had a greater effect on various measured parameters than did particle size. Pelleting evened out differences in particle size distribution between treatments and, as a result, wheat particle size had no effect on the performance of broilers fed pelleted diets. In contrast, the second experiment (Chapter 5) showed that differences in particle size distribution persisted between diets after pelleting and, as a result, coarse grinding of wheat or maize improved broiler performance compared to those fed diets based on fine particles. These results may be related, in part, to changes in size distribution following pelleting. In mash diets, inconsistency in performance reponses were found. In the first experiment (Chapter 4), coarse grinding of wheat improved weight gain and feed per gain compared to medium grinding. In the third experiment (Chapter 6), however, grinding particle size had no influence on broiler performance. The observed discrepancy suggests involvement of other factors such as wheat cultivar and grain hardness. Data reported in Chapter 6 showed that xylanase supplementation improved feed per gain of birds fed the coarse particle size diet, but had no effect on those fed the medium particle size diet. In Chapter 7, there was a significant interaction between wheat hardness and xylanase supplementation due to the improved feed per gain and AMEn of birds maintained on hard wheat-based diet, while there was no effect of xylanase on sort wheat-based diet. These findings suggest that the efficiency of exogenous enzymes is influenced by both particle size and wheat hardness. Data reported in Chapter 7 showed that inclusion of soft or hard whole wheat pre-pelleting produced different particle size distributions in the pelleted diets. This suggested that hardness of the grain must be considered when choosing whole wheat for inclusion in broiler diets. Data on the effect of feed particle size on its subsequent distribution in poultry digesta are scanty. Results reported in Chapters 4 and 5 showed that there was no effect of feed particle size within feed form on duodenal digesta particle size. On the other hand, particle size of duodenal digesta was influenced by feed form (mash vs. pellet). Wheat hardness was also found to influence the particle size of proximal (duodenum and jejunum) intestinal digesta (Chapter 7). These results indicated that the gizzard does not uniformly reduce the size of all particles. However, the gizzard appears highly efficient in grinding large particles, although some large particles escape the grinding. The final experiment demonstrated that the effects of insoluble fibre on digestive tract development and broiler performance differed depending on the fibre source. Wood shavings, a source of coarse insoluble fibre, increased relative gizzard size and improved corrected feed per gain and ileal starch digestibility. In contrast, cellulose, a source of fine insoluble fibre, had no influence on these parameters. In conclusion, dietary manipulations, which stimulated gizzard development, positively influenced broiler performance and starch digestibility. The findings of this thesis suggest that energy savings during feed processing could be achieved by coarse grinding of grains with no adverse effect on broiler performance and that cereals used in broiler diets can be ground more coarsely than the current practice. Wheat hardness appears to be an important criterion to consider when choosing a cultivar for whole wheat inclusion in broiler diets. Another major finding was that the effectiveness of exogenous xylanase in wheat-based diets could be improved by considering factors such as particle size and wheat hardness.