Role of Insoluble Fiber on Gizzard Activity in Layers

Transcription

1 2005 Poultry Science Association, Inc. Role of Insoluble Fiber on Gizzard Activity in Layers H. Hetland,*,1 B. Svihus,* and M. Choct *Department of Animal and Aquacultrual Sciences, Agricultural University of Norway, Ås, Norway; and School of Rural Science and Agriculture, University of New England, Armidale, Australia Primary Audience: Egg Producers, Researchers, Nutritionists, Feed Manufacturers SUMMARY Effect of access to wood shavings on gizzard activity was examined for birds fed pelleted wheat and oat diets with or without whole cereal inclusion. Layers on litter floor fed wheat diets with access to coarse wood shavings showed up to 60% higher weight of the gizzard and its content than caged layers fed the same diets without access to wood shavings. No such effect was found by feeding oat diets. Thus, a significant interaction was found, indicating that the appetite for wood shavings may be dependent of fiber level of the diet. Appetite for wood shavings and paper was examined for birds fed wheat and oat diets in 2 other experiments. The intake of wood shavings and paper by birds fed a wheat-based diet was numerically twice as high as in birds fed an oatbased diet. However, the individual variation was remarkably high. Neutral detergent fiber (NDF) concentration in the gizzard of birds fed the oat diet was up to twice (P < 0.05) the fiber concentration in the gizzard of birds fed the wheat diet. Passage of structural fibers through the gizzard and the appetite for feathers in the absence of structural fibers were also studied in an experiment using diets based on rice and casein. Coarse fiber structures were observed to accumulate in the gizzard. In the absence of fiber, birds ate feathers, indicating that birds may eat feathers to compensate for the lack of structural components in the feed. Key words: insoluble fiber, gizzard, digestion, layer 2005 J. Appl. Poult. Res. 14:38 46 DESCRIPTION OF PROBLEM During the previous decade, use of whole wheat (WW) mixed with a pelleted protein concentrate has become a common practice in European broiler farming because the inclusion of whole grains in poultry diets can have beneficial effect on nutrient digestion [1, 2] and feed use [3, 4, 5, 6]. One of the important roles of whole grains has been associated with their ability to stimulate the activities of the gizzard [1, 2]. This, in turn, is believed to be related to physical structures of whole grains. The major chemical component important to the structural integrity of grains is the insoluble fiber, which makes up the main part of the cell wall architecture. Indeed, insoluble fiber itself has shown beneficial effects on nutrient digestion [2, 7, 8, 9] and gizzard activities [8, 9, 10]. Recent research has shown that digesta passing through the gizzard have a remarkably consistent particle size distribution with the majority of particles being smaller than 40 µm in size regardless of the original feed structure [1]. The fact that gizzard 1 To whom correspondence should be addressed: harald.hetland@iha.nlh.no.

2 HETLAND ET AL.: INSOLUBLE FIBER AND GIZZARD ACTIVITY 39 TABLE 1. Composition of the diets (g/kg) used in experiments 1 to 4 Ingredient Wheat diet Oat diet Wheat diet Rice diet Commercial Experiment and Wheat Oats Rice 700 Sorghum Millrun 50 Soybean meal Fish meal Fish ensilage Casein 160 Meat and bonemeal 20 Cottonseed meal 40 Soybean oil Canola oil 30 Sunflower oil 3 Monocalcium phosphate Dicalcium phosphate Ground limestone Shell meal Sodium chloride Sodium bicarbonate Vitamin and mineral premix Manganese oxide Titanium dioxide 5.0 DL-Methionine L-Lysine L-Threonine Choline chloride Carotenoid mixtures Avizyme Avizyme Betain Calculated nutrient contents per kilogram: AME n, MJ; CP, g; lysine, 7.77 g; methionine, 4.23 g; methionine+cysteine, 6.7 g; threonine, 5.7 g; calcium, 36 g; available phosphorus, 4.8 g. Analyzed natural detergent fiber content, 107 g. 2 Calculated nutrient contents per kilogram: AME n, MJ; CP, g; lysine, 8.1 g; methionine, 4.2 g; methionine+cysteine, 6.8 g; threonine, 5.6 g; calcium, 37.7 g; available phosphorus, 4.1 g. Analyzed natural detergent fiber content, 164 g. 3 Calculated nutrient contents per kilogram: AME n, 11.4 MJ; CP, 160 g; crude fat, 36 g; lysine, 7.9 g; methionine, 4.2 g; methionine+cysteine, 6.7 g; threonine, 5.8 g; calcium, 36 g; available phosphourus, 3.2 g. Analyzed natural detergent fiber content, 86 g. 4 Calculated nutrient contents per kilogram: AME n, MJ; CP, g; crude fat, 22.0 g; lysine, 7.8 g; methionine, 3.4 g; methionine+cysteine, 5.9 g; threonine, 5.5 g; calcium, 3.9 g; phosphorus, 5.0 g. 5 Vitamin premix provided the following per kilogram of diet: Retinyl acetate, 2.7 mg; cholecalciferol, mg; DL-αtocopheryl acetate, 36 mg; menadione, 4.2 mg; pyridoxine, 3.2 mg; riboflavin, 9.8 mg; Ca-pantothenate, 11.8 mg; biotin, 0.15 mg; thiamine, 2 mg; niacin, 34 mg; cobalamin, mg; folic acid, 1.55 mg, Fe, 50 mg; Mn, 40 mg; Zn, 70 mg; Cu, 10 mg; I, 0.5 mg; Se, 0.20 mg. 6 Provided per kilogram of control diet: retinol 2.42 mg, cholecalciferol 0.72 mg, D-α-tocopherol 0.08 mg, menadione 1.6 mg, thiamine 1.6 mg, riboflavin 4.8 mg, pyridoxine hydrochloride 5 mg, cobalmin 0.16, biotin 0.08, niacin 40 mg, calcium pantothenate 9.6 mg, folic acid 1.6 mg, monensin 80 mg, Mn 64 mg, Fe 48 mg, Cu 6.4 mg, I 0.8 mg, Co 0.24 mg, Mo 0.8 mg. contents have higher fiber content than the feed illustrates that fiber is harder to grind than other nutrients and thus is accumulated in the gizzard [7]. For broilers, turkeys, and layers on floor and in modified cages, litter can be a significant source of insoluble fiber. In addition, recent studies indicate that structural components of the feed or litter ingesta may play a role in preventing cannibalism among layers [11, 12]. If so, such components as wood shavings may also be an important enrichment of housing systems.

3 40 JAPR: Research Report TABLE 2. Relative weight of empty gizzard and gizzard contents in 36-wk-old birds fed pellets with whole or ground wheat or oats in conventional 3-hen cages or on litter floor (experiment 1) 1 Conventional cages Litter floor Pooled standard Item GW WW GO WO GW WW GO WO deviation Empty gizzard, g/kg of live weight Gizzard contents, g/kg of live weight GW = ground wheat; WW = whole wheat; GO = ground oats; WO = whole oats. Thus, the aim of these studies was to investigate the response of birds to coarse wood shavings in gizzard activities and gut weight when they were fed diets low and high in fiber or coarse and regular structure. Furthermore, we examined the effect of fiber with and without gizzard-stimulating properties on the voluntary intake of fiber in birds fed low- and high-fiber diets. MATERIALS AND METHODS Experiment 1 Nonbeak trimmed layers [13] to be used in this experiment were used from another large scale experiment. The birds were obtained at 16 wk of age and were housed in conventional 3- bird cages [14] or in a litter floor system [15]. The birds housed in 3-bird cages were reared in cages, while the birds housed on litter floor were reared on litter floor. In the floor system, wood shavings were used as litter cover, and it was refilled weekly by new wood shavings. Cages and the litter floor system were located in 2 different rooms, both with temperature and light control. Light was given for 10 h from 16 wk of age and incrementally to 15 h at 27 wk of age by following commercial recommendations. Diets were either wheat-based or oat-based (Table 1). Both were fed either as a commonly ground complete diet [ground wheat (GW) and ground oats (GO)] or diets with 40% of the whole cereals incorporated into the pellets [WW and whole oats (WO)]. In the complete diets, all cereals were ground through a 3-mm sieve. The composition of the diets with whole cereal was the same as in the corresponding control diets, except 40% of the wheat or oats (of the total diet) was added whole into the mixer before pelleting. In the WW and WO diets, the shell meal was also taken out of the mixture and given in coarse form on top of the feed in the troughs daily in cages and in separate troughs on litter floor. All feeds were conditioned at approximately 75 C, pelleted, and crumbled at a commercial feed mill. At 36 wk of age, 10 birds per feeding regimen and housing system were weighed and killed by a cranial blow followed by cervical dislocation. The gizzard was weighed with and without its contents. Two to three birds were selected at random from different cages from the cage system, while birds housed on litter floor were picked at random. Because different numbers of bids were taken out of the cages, no statistical analysis was performed. Experiments 2 and 3 Birds and Housing System. Pullets [13] were reared from d 1 in commercial rearing cages without access to litter. At 21 wk of age, 40 birds were moved to 20, 2-bird cages in a room with light and temperature control. Each cage was equipped with 2 separate feed troughs with 1 opening in the cage front for each trough. Light was given for 12 h from 21 wk of age and incrementally up to 16 h at 27 wk of age by following commercial recommendations. Feed Composition and Form. The feed in experiment 2 was based on wheat. Wheat was ground using a hammer mill [16] through a 3- mm sieve. The feed mixture was heated to 75 C in a conditioner [17] and pelleted through a pellet press [18] fitted with a 3-mm die with 42 mm effective thickness and crumbled. In experiment 3 the oat-based feed (GO) from experiment 1 was used (Table 1). Experimental Design, Dissection and Statistical Analysis. Wheat (experiment 2) or oatbased diet (experimant 3) was weighed out accurately into 1 trough for each cage. In addition, wood shavings or paper (processed through a

4 HETLAND ET AL.: INSOLUBLE FIBER AND GIZZARD ACTIVITY 41 TABLE 3. Performance and characteristics of the gizzard in birds fed wheat diets, 23 to 28 wk of age (experiment 2) Wheat Wheat diet + Wheat diet + diet paper wood shavings MSE 1 Feed consumption excluding fiber, g/d Egg production, g/d Egg to feed, kg/kg Empty gizzard, g/kg of live weight 8.9 b 9.9 ab 11.2 a 1.52 Gizzard contents, g/kg of live weight 3.3 b 3.6 b 5.1 a 1.33 Neutral detergent fiber in gizzard, g/kg of DM Bile acids in gizzard, mg/g of DM Total bile acids in gizzard, mg Live weight, g 1,751 1,739 1, a,b Means in a row with different superscript are significantly different (P < 0.05). 1 MSE = Square root of mean square error in the analysis of variable. paper cutter) was weighed out to 7 cages each in experiments 2 and 3. At 28 wk of age, all birds per feeding regimen were weighed and killed by a cranial blow followed by cervical dislocation. The gizzard was weighed with and without its contents. Gizzard contents were analyzed for neutral detergent fiber (NDF) and bile acids. Bile acid concentration of the gizzard contents was determined at the Norwegian School of Veterinary Science, Oslo, Norway, using the Enzabile kit [19]. Data from experiments 3 and 4 were analyzed separately using the general linear model procedure of SAS software [20]. Differences between treatments were determined using the least significant difference test. Residual standard deviation was used as a measure of randomness. Experiment 4 Birds and Housing System. A rice-based control diet (as described in Table 1) with a very low fiber level (analyzed nonstarch-polysaccharide contents = 8 g/kg), the control diet with coarse oat hulls (OH-Coarse), the control diet with finely ground oat hulls (OH-Fine), and a commercial diet were manufactured. The diets with oat hulls were made by mixing the control diet with fine and coarse oat hulls, respectively, in the ratio 1:10 prepelleting. Analyzed content of nonstarch-polysaccharides of the oat hulls was 582 g/kg. The coarse oat hulls consisted of large flakes of hulls from commercial dehulling of oats, without further grinding except in the pelleting process. The fine oat hulls were ground to a powder on a laboratory hammer mill through a 0.5-mm sieve. Birds, Housing, and Dissection. One hundred and fifty commercial layers [21], 68 wk old, were placed in single-bird cages with individual feeders. Prior to the experiment, the birds were fed a commercial diet in similar cages. To study the passage of structural fiber through the gizzard, the OH-Fine and OH- Coarse diets were fed to 36 birds each for 1 wk to get accustomed to the respective fiberenriched diets. During the next 10 d, all these birds were fed the control diet to empty the digestive tract of fiber. Prior to the trial day, the birds were fasted overnight. The birds were given access to excess amounts of OH-Fine and OH-Coarse diets, respectively, for 30 min, and the consumption was measured. Thereafter, the OH-Fine and OH- Coarse diets were replaced by the control diet, and consumption was again measured. Prior to feeding (t = 0) and after 2, 4, 8, 24, and 48 h, 6 birds for each feed were killed and dissected. All the contents of the crop and gizzard were collected and stored in a freezer until freezedrying. The remaining 78 birds were used to study feather pecking. Prior to the start of the experiment (d 0), 6 birds were examined to determine whether the population of birds had pecked and swallowed feathers. All 4 feeds were weighed out to 18 birds each. At d 3, 7, and 14, 6 birds from each feed were killed and dissected. The gizzard was opened, and its contents were collected in jars for freeze-drying. Freeze-dried ma-

5 42 JAPR: Research Report TABLE 4. Performance and characteristics of the gizzard for birds fed oat diets, 23 to 28 wk of age (experiment 3) Oat Oat diet + Oat diet + diet paper wood shavings MSE 1 Feed consumption excluding fiber, g/d Egg production, g/d Egg to feed, kg/kg Empty gizzard, g/kg of live weight Gizzard contents, g/kg of live weight Neutral detergent fiber in gizzard, g/kg of DM Bile acids in gizzard, mg/g of DM Total bile acids in gizzard, mg 42.2 a 26.5 b 29.0 b Live weight, g 1,615 1,611 1, a,b Means in a row with different superscript are significantly different (P < 0.05). 1 MSE = Square root of mean square error in the analysis of variable. terial was weighed before gentle grinding. Feathers were separated and weighed for each bird. Chemical Analyses, Calculations, and Statistical Analysis. Total fiber analysis was performed using the AOAC alditol acetate procedure [22]. Amount of oat hulls passed gizzard (% of entered gizzard) was calculated as follows: 100 [(oat hulls in gizzard 100)/ (ingested oat hulls oat hulls in crop)] The experiment was designed to be completely balanced. However, 7 of the birds used to study feather pecking, distributed among the rice-based diet treatments (only d 7 and 14), were excluded from the analysis because of their very low feed intake (from 13 to 50 g/d). Data for passage of oat hulls and feather contents in the gizzard were not normally distributed, and thus no statistical analysis is presented for these data. The data for feed consumption and gizzard weights were analyzed in a 2-way ANOVA using the general linear model procedure of SAS software [20]. RESULTS AND DISCUSSION The weight of the empty gizzard did not differ with feeding pellets with ground or whole cereals (Table 2). However, a tendency (P = 0.066) for increased weight of gizzard contents was found with whole cereals in the feed. Birds on litter floor had up to 60% higher (P < 0.05) weight of empty gizzard and gizzard content weights than birds in cages. However, the difference in gizzard weight and gizzard contents weight due to housing system was greater for birds fed wheat diets than those for birds fed oat diets. Thus, significant (P < 0.05) interactions were found between cereals and housing systems. The significant (P < 0.05) interaction between cereal and feed structure was due to an increase in the empty gizzard weight when GO were substituted for WO, while no difference was found for the wheat diets. Neither paper nor wood shavings affected performance (Table 3 and 4). While carrying out experiment 3, a warm weather period caused difficulties for maintaining recommended temperature. This may explain the lower egg production for the oat diet compared with the wheat diet. Weights of the empty gizzard and gizzard contents of birds fed the wheat diet were increased due to their access to wood shavings, but no such effect was apparent in birds fed the oat diet. Access to paper did not affect gizzard weight in either experiment. The NDF concentration was considerably higher in gizzard contents than in the feed in all treatments. The NDF concentration in gizzard was twice as high (P < 0.05) in birds fed the oat diet as those fed the wheat diet. Bile acid concentration of gizzard contents was similar for wheat and oat diets and also similar with and without access to wood shavings or paper. However, total bile acid content was more than doubled in birds fed oats than wheat diet, proportional to the difference in gizzard contents.

6 HETLAND ET AL.: INSOLUBLE FIBER AND GIZZARD ACTIVITY 43 TABLE 5. Daily consumption of paper and wood shavings for birds fed wheat and oat diet (experiment 2 and 3) Wheat diet Oat diet Wood Wood Paper shavings Paper shavings Mean, g/bird Minimum, g/bird Maximum, g/bird Numerically, birds fed the wheat diet consumed almost double the amount of wood shavings than those fed the oat diet, while consumption of paper was 6 times higher for birds fed the wheat diet than for birds fed the oat diet (Table 5). The numerical distance between the mean and extreme values was observed to be up to 3 times the mean. Approximately 6 and 3% of ingested oat hulls were found in the crop after 2 and 4 h, respectively. Thereafter, no significant amount of oat hulls was found in the crop. The amount of oat hulls that had passed the gizzard (percentage of entered gizzard) at different times is illustrated in Figure 1. Since only the data for feed consumption and gizzard contents were normally distributed, statistical analysis of the data from experiment 4 is presented. A numerically higher amount of oat hulls in the gizzard was found for the OH-Coarse diet than OH- Fine diet. Approximately 50% of the ingested oat hulls from the OH-Coarse diet and 90% of the ingested oat hulls from OH-Fine diet had passed the gizzard after 2 h. No oat hulls were found in birds fed OH-Fine diet after 48 h, whereas as much as 30% of the ingested oat hulls were found in the gizzard of birds fed OH- Coarse diet. No significant amount of feathers was found in birds prior to the start of the experiment (0.00 to 0.02 g). A clearly lesser amount of feathers was found in the gizzard contents of birds fed the commercial and OH-Coarse diets than those fed control and OH-Fine diets, despite high individual variation within a treatment (Table 6). Birds fed the OH-Coarse and commercial diets showed higher (P < 0.05) amounts of gizzard contents than those fed the control and OH-Fine diets. The gizzard contents in birds fed OH- Coarse were observed to consist mainly of oat hulls. The gizzard is known as the pacemaker organ in birds, regulating the particle size of food FIGURE 1. Passage of oat hulls through the gizzard.

7 44 JAPR: Research Report TABLE 6. Feed consumption, gizzard contents, and feathers in the gizzard (experiment 4) Control Commercial Standard Item Day diet OH-Fine 1 OH-Coarse 1 diet deviation Daily feed consumption, g Gizzard contents excluding feathers, g DM Feathers in gizzard, g OH-Fine = the control diet with finely ground oat hulls; OH-Coarse = the control diet with coarse oat hulls. entering the small intestine for downstream digestion. Feeding studies with broilers have shown that the gizzard becomes stimulated when whole cereals replace ground cereals [1, 3, 8]. Replacing 50% GW with the same quantity of GO gives the same increase in gizzard weight as replacing 50% GW with WW [1]. A relatively small amount of insoluble fiber (e.g., 10% oat hulls coming from 50% of oats) stimulates the gizzard to the same extent as 50% WW. The current data indicate that the gizzard weight is less affected by cereal structure in layers. However, insoluble fiber seems to play an even more profound role for gizzard activity in the more mature digestive tract of the layer. This corresponds with an earlier experiment with layers in which consumption of 4% of feed as wood shavings resulted in 50% heavier gizzard, whereas including 40% WW in the wheat-based diet increased the gizzard weight by only 10% [7]. In the current study, over 50% heavier gizzards in birds on litter floor than in cages appeared to be a result of the birds consuming the litter materials. Visual observations of gizzard contents showed that the birds housed in a litter floor system had consumed a considerable amount of wood shavings. The interaction between cereal-grain type and system may indicate that the voluntary intake of insoluble fiber from the floor varies with dietary insoluble fiber level. The numerical difference in gizzard weight and its contents due to housing system was small for birds fed oat diets and large for those given wheat diets. Since oats contain considerably more fiber than wheat, the appetite for wood shavings seems to be related to the fiber content of the diet. This was also supported by the results of experiments 2 and 3 in which the intake of wood shavings by birds fed a wheat-based diet was almost twice that of birds fed an oat-based diet. However, the very high individual variation makes these results less conclusive. In contrast to digestible nutrients, insoluble fiber plays a physiological role in the digestive tract by interacting with gut functions, nutrients and enzymes [23]. Thus, the birds may perceive the physiological response less sensitively than for digestible nutrients, leading to vast variation in the intake of wood shavings and paper. Individual pecking and searching behavior may also influence the consumption of indigestible fiber components. In a previous study in which wood shavings were sprinkled on top of the feed, a considerably higher consumption was observed than in the current experiment. This indicates that how and where structural components, such as wood shavings, are presented may influence the bird s ability to consume these materials [7]. In poultry, insoluble dietary fiber has shown beneficial effects on starch digestion [7, 8, 9, 10]. It has been speculated whether the beneficial effect of insoluble fiber on digestion is a result of increased gizzard activity. The higher level of total bile acids in the gizzard by feeding oats compared with wheat suggests that structural components increase digesta reflux, possibly through increased gizzard activity. This result agrees with a previous study [7] in which insoluble fiber increased total bile acids in the gizzard. That insoluble fiber decreases the nutrient concentration may also play a role by increasing digestive juices and substrate relationship, which is supported by the fact that fine cellulose

8 HETLAND ET AL.: INSOLUBLE FIBER AND GIZZARD ACTIVITY 45 powder has also shown beneficial effects on starch digestion in wheat diets [2]. Coarse feed particles need to be ground to a certain critical size before they can leave the gizzard [24, 25], causing the volume of gizzard contents to increase when diets with whole cereals or insoluble fiber are fed [7]. The current data and previous experiments show that the fiber level of the gizzard contents is about twice that of the feed [7]. This means that fiber structures accumulate in the gizzard and that retention time of insoluble fiber is longer than for other nutrients. Fibers, such as cereal hulls, are very solid and can probably be retained for a long time in the gizzard. In contrast, whole cereals that mainly consist of starch granules and protein will be dissolved very fast in the acidic gastric fluid in the gizzard. Thus, the gizzard activity is more strongly stimulated by fiber structures compared with whole cereal structures. Accumulation of fiber in the gizzard and thus its slower passage out of the gizzard are contrary to the conventional theory that insoluble fiber speeds up feed passage. However, it must be stressed that this phenomenon may only be true for the coarse, insoluble fiber fraction. Recent work [10, 26] indicates that the passage time of fine particles decreases when coarse fiber is fed to broilers. Similar to fine cellulose powder [2], paper materials did not stimulate gizzard activity. The higher consumption of paper than wood shavings by feeding the wheat diet may indicate that the appetite for fiber is triggered by a need for gizzard-stimulating components. Birds with access to wood shavings easily get the gizzard stimulated by the consumption of a small amount of the material. In contrast, birds with access to paper get no such response of fiber consumption. This lack of gizzard stimulation by paper may be a reason why the birds with access to paper showed a considerably higher fiber consumption than those with access to wood shavings. The similar consumption levels of paper and wood shavings by birds fed the oat diet may be due to the satisfaction of their fiber needs for gizzard stimulation by the high fiber content of the diet. An empty gizzard in birds fed the rice and OH-Fine diets was probably due to the low-fiber diet and the finely processed oat hulls passing through the gizzard without stimulating it. This reinforces the hypothesis that the holding of food in the gizzard depends on the particle size of the food and its insoluble fiber contents. In other words, the gizzard will not retain food if it has no need for grinding. Possibly, the bird has a need for fibrous or structural feed components to maintain a normal gizzard. In the current study, birds fed a high-fiber commercial diet and a diet containing coarsely ground oat hulls had a negligible amount of feathers in their gizzards compared with those fed a low-fiber diet and a diet containing finely ground oat hulls. This indicates that feather-pecking behavior may be partly related to the feed structure and consistency. Since the birds were housed in singlebird cages, this phenomenon could not be caused by cannibalism and aggressive pecks. Thus, feather pecking and swallowing may be driven by a need for gizzard stimulation. The gizzard has been found to play a major role for gastroduodenal reflux of digesta [27]. An empty gizzard will not have feed stimuli and as such will not be able to regulate downstream digestive processes. This, once again, supports the hypothesis that birds may have a requirement for fiber for stimulation of the anterior digestive tract and that a functional gizzard needs contents with structural components. CONCLUSIONS AND APPLICATIONS 1. The gizzard has an excellent ability to grind coarse components. Coarse particles are selectively retained in the gizzard until they are ground to a certain critical size. 2. Structural components in the form of whole cereals and coarse water-insoluble fiber can improve feed use in birds fed highly concentrated diets. Improved feed use is at least partly caused by increased digestibility of starch and may be due to increased gizzard activity.

9 46 JAPR: Research Report REFERENCES AND NOTES 1. Hetland, H., B. Svihus, and V. Olaisen Effect of feeding whole cereals on performance, starch digestibility and duodenal particle size distribution in broiler chickens. Br. Poult. Sci. 43: Svihus, B., and H. Hetland Ileal starch digestibility in growing broiler chickens fed a wheat-based diet is improved by mash feeding, dilution with cellulose or whole wheat inclusion. Br. Poult. Sci. 42: Kiiskinen, T Feeding whole grain with pelleted diets to growing broiler chickens. Agric. Food Sci. Finland 5: Olver, M. D., and A. Jonker Effect of choice feeding on the performance of broilers. Br. Poult. Sci. 38: Svihus, B., O. Herstad, C. W. Newman, and R. K. Newman Comparison of performance and intestinal characteristics of broiler chickens fed on diets containing whole, rolled or ground barley. Br. Poult. Sci. 38: Preston, C. M., K. J. McCracken, and A. McAllister Effect of diet form and enzyme supplementation on growth, efficiency and energy utilisation of wheat-based diets for broilers. Br. Poult. Sci. 41: Hetland, H., B. Svihus, and Å. Krogdahl Effects of oat hulls and wood shavings on digestion in broilers and layers fed diets based on whole or ground wheat. Br. Poult. Sci. 44: Rogel, A. M., D. Balnave, W. L. Bryden, and E. F. Annison Improvement of raw potato starch digestion in chickens by feeding oat hulls and other fibrous feedstuffs. Aust. J. Agric. Res. 38: Rogel, A. M., D. Balnave, W. L. Bryden, and E. F. Annison The digestion of wheat starch in broiler chickens. Aust. J. Agric. Res. 38: Hetland, H., and B. Svihus Effect of oat hulls on performance, gut capacity and feed passage time in broiler chickens. Br. Poult. Sci. 42: Aerni, V., H. El-Lethey, and B. Wechsler Effect of foraging material and food form on feather pecking in laying hens. Br. Poult. Sci. 41: El-Lethey, H., V. Aerni, T. W. Jungi, and B. Wechsler Stress and feather pecking in laying hens in relation to housing conditions. Br. Poult. Sci. 41: The strain Lohmann Selected Leghorns (LSL), Cuxhaven, Germany. 14. Haho cage system, Elverum, Norway. 15. Vencomatic, Eersel, The Netherlands. 16. Model E TF, Muench, Wuppertal, Germany. 17. Double conditioner, Mnch-Edelstahl, Germany. 18. RMP , Mnch-Edelstahl, Germany. 19. Nycomed Pharma AS Diagnostics, Torshov, Norway. 20. SAS Institute Release 8.2. SAS Institute Inc., Cary, NC. 21. ISA Brown, St. Brieuc, France. 22. Theander, O., P. Åman, E. Westerlund, and H. Graham The Uppsala method for rapid analysis of total dietary fiber. Pages in New Developments in Dietary Fiber. I. Furda and C. J. Brine, ed. Plenum Press, New York. 23. Krogdahl, Å Antinutrients affecting digestive functions and performance in poultry. Proc. 7th Eur Poult. Conf., Paris 1: Clemens, E. T., C. E. Stevens, and M. Southwort Sites of organic acid production and pattern of digesta movement in the gastrointestinal tract of geese. J. Nutr. 105: Moore, S. J Food breakdown in an avian herbivore: Who needs teeth? Aust. J. Zool. 47: Svihus, B., H. Hetland, M. Choct, and F. Sundby Passage rate through the anterior tract of broiler chickens fed on diets with ground and whole wheat. Br. Poult. Sci. 43: Duke, G. E Recent studies on regulation of gastric motility in turkeys. Poult. Sci. 71:1 8.