The Feasibility of Using Nutritional Modifications to Replace Drugs in Poultry Feeds

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1 2002 Poultry Science Association, Inc. The Feasibility of Using Nutritional Modifications to Replace Drugs in Poultry Feeds G. G. Mateos, 2 R. Lázaro, and M. I. Gracia Departamento de Producción Animal, Universidad Politécnica de Madrid, Madrid, Spain Primary Audience: Nutritionists, Researchers, Poultry Technicians SUMMARY The restrictions in the use of in-feed antibiotics and proteins of animal origin in many European countries have increased the incidence of enteric disorders in poultry. Management and dietary changes have been suggested to reduce the negative effects of enteritis on broiler performance and carcass quality. Practices used in this respect are enhancement of the development of the gastrointestinal tract, improvement of nutrient digestibility, and modification of the conditions of the intestinal contents to promote a balanced growth of native flora. The most promising areas of research are the use of enzymes and the inclusion of whole grains in the diet. Areas of interest, but needing large amounts of basic information, include studies on the interrelationship between diet composition and the microbiota within the gastrointestinal tract. Also, the influence of processing of diets and ingredients and of the inclusion of natural additives on digestive physiology and microflora growth deserves attention. In conclusion, dietary manipulation of the diet together with management changes will reduce to manageable levels the problems associated with the ban of use of growth promoters in broiler feeds. Key words: growth promoter, commercial poultry production, diet modification 2002 J. Appl. Poult. Res. 11: DESCRIPTION OF PROBLEM Antimicrobial agents are used in animal production for a variety of purposes, including therapy, disease prevention, and improvement of productivity. Addition of certain antibiotics to feed at low levels for an extended period of time is a common practice in the poultry industry and provides economic benefits by increasing weight gain and improving feed efficiency from 1 to 5% [1]. Antibiotics are thought to increase productivity through their activity on the microflora of the gastrointestinal tract (GIT) and are especially useful in young animals where they constitute the main tool for the control of subclinical diseases under intensive production systems. Intestinal organisms associated with reduced growth of the bird that are inhibited by these antibacterial agents have not been conclusively identified, but experimental data provide evidence that Clostridium perfringens, a gram-positive microorganism, is a causative agent [2]. There are concerns among producers, feed manufacturers, retailers, consumers, and regulatory 1 Presented as part of the Informal Nutrition Symposium Making Sense of Scientific Research and Applying It Properly at the 91st Annual Meeting of the Poultry Science Association, Newark, Delaware, August 11 14, To whom correspondence should be addressed: ggmateos@pan.etsia.upm.es.

2 438 agencies regarding the current systems of production that supply poultry meat and eggs. Issues of major interest include animal welfare, environmental management, and safety of human food and animal feeds. In this respect, there is a growing concern about the use of growth promoters of antibiotic origin. Published data indicate that indiscriminate use of in-feed growth promoters increases the survival of strains resistant to antibiotics used in human medicine and the chances of transferring the resistance to other bacteria. New regulations in the European Union are restricting the marketing of most drugs to eventually banning of their use altogether. In fact, it has been proposed to phase out, by January 2006, authorizations of the four antibiotic feed additives (monensin, salinomycine, avilamycine, and flavophospholipol) that are currently on the market in the European Union. The European Federation of Animal Health has published data indicating that a total of 4,700 tonnes of antibiotics were administered to farm animals in 1999, which represents 35% of the total consumption of these antibiotics in the European Union [3]. From this quantity, 786 tonnes, equivalent to 6% of total use, were included in feeds as growth promoters, which is less than half the quantity used in Also, stricter measures will be introduced for the use of coccidiostats of antibiotic origin, including presentation of a new dossier for re-evaluation within a 4-yr period. Many European integrated poultry companies are producing feeds for poultry based exclusively on vegetable feedstuffs without any growth promoter. Under these circumstances, problems related to necrotic enteritis (NE), feed passage, and other enteric diseases are frequently reported; therefore, alternatives to the use of growth promoters are required. A myriad of natural products, including organic acids, probiotics, prebiotics, plant extracts, and immune stimulants have been proposed for the control of pathogens in the GIT, but data supporting their effectiveness are equivocal. A second option, compatible with the utilization of natural additives, consists of manipulating the composition and nutrient content of the diet together with changes in some management practices at the feed mill and in the field to improve health status of the GIT. JAPR: Symposium POSTHATCH NUTRITION AND PHYSIOLOGICAL STATUS OF THE GIT Physiological studies have shown that the GIT of birds responds to the digestive contents and therefore to the composition of the original feed. Also, physiological studies have shown that the response is modulated by the health status of the gut. The bird adjusts its response in terms of release of enzymes and rate of passage to maximize digestion and absorption of the end products. When the capacity of the system is insufficient, physiological, hormonal, and immunological responses take place with a reduction of the appetite and mechanical diarrhea to eliminate the cause of the problem. Eventually, there will be a modification within the GIT with a rapid growth of pathogenic bacteria to the detriment of native beneficial microflora. Therefore, in the absence of antibiotics, strategies to minimize enteric diseases associated with microflora changes are needed. A potential solution is to use more digestible feeds but this is an expensive option. A second possibility consists in improving the structure and health status of the gut, an option that can be addressed through different strategies [4, 5]. A third possibility is to improve the digestibility of available feedstuffs by processing ingredients and diets and the use of exogenous enzymes (ES). The nutritional requirements of baby chicks and poults after hatching are not precisely known. At hatch the absorptive mechanisms are well developed, but not totally developed, and the digestive capacity is not fully functional [4, 6, 7]. At early ages, birds prioritize needs, and the allometric coefficient for growth is greater for supplier organs than for demand organs [5]. Gracia et al. [8] have reported that in the broiler chick, the maximal weight (g organ/g of BW) of the proventriculus, gizzard, pancreas, liver, and small intestine is observed at 4.6, 3.5, 7.8, 5.5, and 7.8 d of age, respectively (Table 1). Digestion and absorption of nutrients early in life depends primarily on pancreatic enzyme activity [9, 10], but the pancreas is functionally immature when chicks hatch. Therefore, the digestibility of proteins, lipids, and starch is incomplete during the first days of life.

3 MATEOS ET AL: INFORMAL NUTRITION SYMPOSIUM 439 TABLE 1. Changes with age in relative weights of digestive organs of the chick (% BW) Age A (d) Day of maximal relative growth B SEM A B Proventriculus to 5 Gizzard to 4 Pancreas to 9 Liver to 8 Small intestine to 7 A P < with age (0, 4, 8, 15, 21 d). B Source for A: Gracia et al. [8]; source for B: Sell [4]. Early development of the GIT requires rapid access to feed and water and adequate sources of energy and protein in the prestarter diet. In commercial operations, poultry are removed from the incubator when a majority of the birds have hatched. Thus, early-hatched chicks remain without feed for more than 36 h since placement on the farm is further delayed due to hatchery processing and transportation. Under these circumstances, the capability of the chick to digest feed and to cope with environmental and management stresses is limited. It has been assumed that at hatch, the lipid fraction of the residual yolk sac is an important source of energy, but this may not be the case. The yolk sac at hatch contains less than 1 g of triglycerides, an amount that diminishes rapidly and is almost absent by the third to fourth day of life [7, 11]. Therefore, residual triglycerides in the yolk sac are not a good reservoir, and early access to feed is critical for the newborn chick [5]. Early access to feed and water stimulates growth of the GIT and its absorptive capacity and improves gut integrity and subsequent performance [7, 12, 13, 14]. Lilburn [5] pro- posed feeding a combination of uniquely processed, highly digestible, high-protein ingredients in combination with high levels of corn for the first 10 d of life to meet the energy and protein needs of very young poults. Batal and Parsons [15] observed that administration of a semisolid hydrated nutritional supplement based on protein and carbohydrates with no fat added has a beneficial effect on subsequent utilization of the energy of a corn-soybean meal diet. Noy and Sklan [13] reported that birds receiving a posthatch supplement have greater body weights through 21 d of age than chicks and poults that were fasted for 34 or 48 h, respectively. Batal and Parsons [16] studied the energy value for chicks of corn diets having soybean meal or rapeseed meal as the main protein source and observed that in both cases the ME n was very low at 2 and 4 d of age but increased afterward. When a dextrose-casein diet was used, the ME n was high at 2 d, and no great improvements were observed with age. Metabolizable energy, as a percentage of gross energy at 2 d, was 66% for the corn-soybean meal diet but 88% for the dextrose-casein diet, indicating TABLE 2. Influence of age on the ME n :gross energy ratio of several soy oil diets for chicks (%) A Age Corn-soybean Corn-canola Corn-synthetic Dextrose- Pooled (d) meal meal amino acids casein SEM cy 63 bz 84 cx 88 bw cy 64 bz 84 cx 88 bw bx 65 by 87 bw 88 bw ax 68 ay 89 aw 88 bw ax 69 ay 89 aw 89 aw 0.4 Pooled SEM A Source: Batal and Parsons [16]. a c Means within a column with no common superscript differ significantly (P < 0.05). w z Means within a row with no common superscript differ significantly (P < 0.05).

4 440 JAPR: Symposium TABLE 3. Influence of postchatch fasting period on nutrient digestibility in broilers A,B Apparent fecal digestibility C (%) ME n BW,7d Fasting (h) OM D CP EE E (Mcal/kg) (g) SEM (n = 45) A Source: Aranibar [18]. B P < for all nutrient digestibilities and ME n and P < 0.01 for BW. C Average value of determinations at 3 and 7 d postfeeding. D Organic matter. E Ether extract. that the dextrose-casein should be preferred in diets for very young chicks (Table 2). Sulistiyanto et al. [17] also indicated that casein was better utilized than fish meal and soybean meal for chicks less than 10 d of age. They also found that energy from corn was utilized better than energy from wheat and sorghum but not better than energy from different sources of fat. Aranibar [18] conducted a trial to measure apparent fecal digestibility of nutrients of a cornsoybean meal diet in chicks fasted for 12 or 36 h after hatching. At 3 and 7 d postfeeding, the digestibility of most nutrients was higher for birds fasted 36 h than for those fasted 12 h (Table 3), which is in disagreement with most published information [19]. The reason for the discrepancy is not known, but in that study, Aranibar [18] compared birds with the same interval postfeeding and not with the same chronological age as in most published papers. At 21 d, however, no differences were observed between treatments for any of the traits (data not shown) [18]. In a second trial, Aranibar [18] compared diets (0 to 10 d) that included fats (6.8% of sunflower oil, fish oil, or lard) with diets that included carbohydrates (15% of starch or sucrose) as the main source of energy. At 10 d of age no differences were detected for daily gains, but birds fed the supplemented fat diets had better (P < 0.05) feed conversion than birds fed the diets containing carbohydrates (Table 4). This observation was expected because of the different energy concentration of the two type of diets used. Once the birds received a common corn-soybean meal diet (10 to 21 d), no differences among treatments were detected. In a third trial [18], the productive performance of chicks fasted 12 or 36 h and fed diets varying in ME n content (2.82 to 3.18 Mcal/kg) and in total lysine (1.22 to 1.42%) was compared. At 10 d of age, fasting increased feed intake and daily gain but did not affect feed conversion, whereas ME n and lysine contents of the diet improved feed conversion (Table 5). At 10 d of age, all of the birds received a common diet, and at 21 and 42 d of age no differences were detected in performance or digestibility of nutrients due to previous treatment. Other results from our laboratory indicate that delaying access to feed for up to 48 h or changing the nutrient content (energy and protein level) or the major energy source (fats of different fatty acid profile, starch, and sucrose) of the prestarter (0 to 10 d) diet did affect some digestive and productive parameters from 0 to 10 d of age, but the differences disappeared thereafter. These results agree with Noy and Sklan [20] who used a series of diets during the first week of age in which the level of fat, protein, and cellulose varied widely with differences in broiler performance at Day 7, but by Day 18, when all the birds received a common diet, no treatments effects were observed. TABLE 4. Source of energy and productivity in broilers from0to10dofage A,B Energy source Daily gain (g) Feed conversion (g/g) Sunflower oil C b Fish oil C b Lard C b Starch D a Sucrose D a SEM (n = 5) A Source: Aranibar [18]. B P > 0.05 for daily gain and P < 0.05 for feed conversion. C Contained 3.12 Mcal ME/kg and 6.8% added fat. D Contained 2.91 Mcal ME/kg and 15% added carbohydrate.

5 MATEOS ET AL: INFORMAL NUTRITION SYMPOSIUM 441 TABLE 5. Influence of fasting and type of diet on performance of broiler chicks from 0 to 10 d postfeeding A Feed intake Daily gain Feed conversion (g/d) (g) (g/g) Fasting (h) b 17.8 b a 18.9 a 1.16 ME n, (Mcal/kg) a a b b c c Total Lys (%) a ab b SEM A Source: Aranibar [18]. a c Means within a column and treatment group with no common superscript differ significantly (P < 0.01). From these trials it was concluded that differences in productivity because of dietary changes in the prestarter feed or a delay in the access to feed tend to disappear with age and that the losses in performance incurred by chicks held without feed for 48 h are equivalent to lengthening the time taken to reach market weight by 2 d. Therefore, at the farm level, where age of the chicks is measured as days postfeeding and not chronologically, no great differences in final performance will be found associated with a moderate delay in access to feed. Also, it appears that once the minimum requirements for nutrients are provided, the influence of the dietary composition of the prestarter feed on subsequent broiler growth is limited. DIGESTIBILITY OF NUTRIENTS The National Research Council [21] assumes that digestibility of raw materials is independent of age. However, numerous reports have shown that the digestibility of nutrients in young poultry increases with age [15, 16, 22]. Early growth of the small intestine is very rapid and exceeds that of body weight until 6 to 8 d of age. The concentration of digestive enzymes is reduced at hatch and increases until 14 d of age, and the villus surface also increases between 4 and 10 d of age. Consequently, dietary nutrients are poorly utilized during the first 10 d posthatching. Work from our laboratory indicates that fat is the nutrient whose digestibility is most affected by age, especially when saturated fats are used in combination with viscous cereals. The ability to absorb dietary lipids is not well developed in the newly hatched chick [7], and lipase activity and bile secretions are not adequate for the first 10 d after hatch [4]. Also, it has been reported that certain nonstarch polysaccharides (NSP) TABLE 6. Influence of age on starch and ether extract fecal digestibility in broilers A Starch B (%) Ether extract C (%) Age (d) A B A B SEM A Source for A: Gracia et al. [8]. Corn-soybean meal diet with 2.7% added lard. Source for B: Gracia et al. [24]. Barleysoybean meal diet with 6% added lard. B Starch: linear, P < C Ether extract: linear and quadratic; P <

6 442 JAPR: Symposium TABLE 7. Influence of age on apparent fecal digestibility of nutrients in New Hampshire Columbian male chicks A Apparent fecal digestibility (%) Age ME n (d) (kcal/kg, DM) Starch Fat Lys Met 0 2 2,970 d 93 c 61 b 78 d 80 c 3 4 3,085 c 93 c 58 b 81 c 82 c 7 3,185 b 97 b 59 b 85 b 87 b 14 3,429 a 99 a 74 a 89 a 92 a 21 3,426 a 99 a 73 a 89 a 92 a SEM A Source: Batal and Parsons [16]. Diets with 5.5% added soy oil. a d Means within a column with no common superscript differ significantly (P < 0.05). have the ability to bind bile salts, lipids, and cholesterol, reducing lipid digestibility [23]. Gracia et al. [8, 24] observed that fecal digestibility of starch and ether extract in broilers increased with age both in a corn and in a barleysoybean meal diet (Table 6). The change in digestibility from 4 to 21 d of age for the cornand barley-based diets were of 2.2 and 2.2% for starch and 15.5 and 18.0% for ether extract, respectively. Also, Batal and Parsons [16] found that the ME n value of a corn-soybean meal diet was low at 2 d and reached a plateau at 14 d of age (2,970 vs. 3,429 kcal/kg DM). The apparent digestibility of starch and fat also increased between these ages by 3.0 and 13.0%, respectively (Table 7). For the first 3 to 5dofage, overall digestibility of lipids in chicks is around 69% but reaches 80% for polyunsaturated fats [5], which indicates that unsaturated fats can be used successfully in prestarter diets for poultry. Noy and Sklan [25] reported that ileal digestibility of nitrogen in a corn-soybean meal diet increased from 78% at Day 4 to nearly 90% at Day 21, indicating that the proteolytic activity in the intestines may not be sufficient in the early posthatch period. Similar data have been reported by Batal and Parsons [16] who found that the apparent digestibility of lysine and methionine in a corn-soybean meal diet increased from 74 and 77% at Day 4 to 88 and 87%, respectively, at Day 21. Researchers have found that the ME n of diets decrease rapidly during the first days after hatching until approximately 4 to 7 d of age, which is followed by a progressive rise until 14 to 21 d of age [8, 15, 16, 22, 24] (Table 8). The reason for the decline at these ages is unknown but might be related to the lack of sufficient activity of the pancreatic enzymes and bile salts, once the phospholipids of the yolk sac disappear from the GIT [22]. DIGESTION OF STARCH AND FACTORS AFFECTING DIGESTIBILITY The starch content of a typical diet for broilers ranges from 34 to 38%, and more than 50% of the ME of poultry feeds is provided by starch. Therefore, starch digestibility is critical for understanding energy utilization by poultry. Starch is composed of two glucose polymers: amylose and amylopectin. Amylose is almost a linear polymer and forms part of the amorphous area of starch. Amylopectin is a branched polymer and gives native starch its crystallinity. The structure and stability of amylopectin differs among starch sources originating the so-called A- (very compact with no space left for water), B- (interior channel filled with water), and C- type (intermediate) starches [26]. In the GIT, starch is hydrolyzed to α-limit dextrins, maltotriose, and maltose and then to glucose. It is generally believed that α-amylase is produced in excess of requirements, at least in the adult bird [27, 28]. However, trials with poultry indicate that for most situations, starch digestion at the end of the ileum is high but incomplete and varies according to feedstuffs, processing of the diet, and age of the bird. Rogel et al. [29] observed that fecal digestibility of starch in crushed wheat increased with age from 85.8% at 3 wk to 96.5% at 7 wk of age and that pelleting improved starch digestibility at 3 wk (77.2 vs. 94.4%) but not at 7 wk (95.1 vs. 97.8%). Weurding et al. [30] found that the

7 MATEOS ET AL: INFORMAL NUTRITION SYMPOSIUM 443 undigested starch fraction of various ingredients varied from 1% for tapioca pellets to 67% for raw potato starch, with intermediate values for cereals (2 to 6%) and legume grains (19 to 28%). Therefore, a variable amount of resistant starch escapes absorption and enters the hindgut, where it can be fermented to volatile fatty acids and benefit the health of the large bowel by reducing intestinal ph, inhibiting pathogen growth, increasing fluid and electrolyte absorption, and directly fueling mucosal cells [26]. Research has shown, however, that only a very limited fraction of the residual starch is fermented by the microflora of the hindgut in healthy broilers [26, 30, 31, 32]. Young birds have a limited capacity to digest starch and the major limiting factor is the accessibility of digestive enzymes. Data from Gracia et al. [8, 24] indicate that the fecal digestibility of starch in a corn-soybean meal diet increased linearly with age from 95% at Day 4 to 97.2% at Day 21 (Table 6), values that are similar to those reported by others [15, 16, 31]. Enzyme accessibility is determined by factors such as the viscosity of the gut content, size and nature of the protective structures surrounding the granules, and structure of the starch. Hesselman and Åman [33] observed that ileum starch digestibility of barley was greater with low-viscosity grains than with high-viscosity grains (88.5 vs. 85.1%). In general, starch in small granules had lower amylose content and is hydrolyzed more rapidly than starch in large granules. Also, starches with low-amylose content are more digestible than starches with highamylose content, because high-amylose starches are less susceptible to amylase attack. In addition, starch A granules are easier to digest than starch B or C granules, and as a consequence, starch from cereals are better utilized by the young chick than starch from legumes. Rice starch has good accessibility, the granule is very small, the amylose content is lowest among cereals, the starch is mostly type A, and the grain does not contain appreciable amounts of β-glucans or xylans. Therefore, rice might be an energy source of choice for prestarter diets for chicks, but data confirming this choice is very limited. The information provided indicate that digestibility of starch is high but incomplete in young birds, especially when fed heat-processed diets rich in legume grains and in the presence of highly viscous cereals. Also, starch digestibility increases rapidly with age [8, 16, 24, 25, 31]. High percentages of resistant starch, defined as the sum of starch derivatives not absorbed in the small intestine of healthy individuals, in the diet may compromise the efficiency in feed conversion of broilers, but its effect on hindgut fermentation and bacteria growth needs further clarification. HEAT PROCESSING OF GRAINS Heat is usually applied to raw materials containing thermo-labile antinutritional factors, such as soybeans. Also, application of heat is common in pelleting, a process that reduces feed wastage and improves performance of broilers. Recently, expanded feed has been introduced into the market because of its beneficial effects on feed hygiene, nutrient digestibility, and feed conversion of broilers [34, 35]. Processes based on heat, shearing, and pressure modify the chemical and physical structures of feeds, which may alter nutrient digestibility, GIT development, and the incidence of enteric disorders. However, heat processing (HP) of cereal and legume grains, at temperatures above 100 C for extended periods of time, a common practice in piglet feeding, is not used to any extent in poultry feeds. The information available on the influence of this technology on digestive physiology and broiler performance is scarce and contradictory [8, 26, 36]. Heat processing disrupts the structure of proteins and granules of starch and changes the physiological properties of the fiber, facilitating accessibility of digestive and ES to nutrients. Also, because of the structural changes produced in the crystalline structure of the starch, HP will accelerate digestive diseases, leading to shifts in the place of starch digestion, which in turn may affect the growth of the different microbial species present in the GIT. On the other hand, HP increases the solubility of NSP [37] and starch, because amylose is released into the solution [26], and might facilitate Maillard reactions within the protein fraction [38], increasing digesta viscosity, reducing lysine availability, and impairing bird performance. Plavnik and Sklan [39] have found that dry extrusion or expansion of a corn diet im-

8 444 JAPR: Symposium TABLE 8. Influence of age in utilization of dietary energy (ME n, Mcal/kg) of corn-soybean meal diets Source of information A C C D D Age (d) A B EXP. 1 EXP. 2 EXP. 1 EXP b 2.97 d 3.16 b c 2.73 d 3.08 c 3.00 c d 2.94 c 3.18 b 3.07 c ab 3.22 a 3.43 a 3.23 b a 3.26 a 3.43 a 3.38 a a d Means within a column with no common superscript differ significantly (P < 0.05). A Source for A: Gracia et al. [8]. Diet with 2.75% lard. Data for as-fed basis. Source for B: Batal and Parsons [15]. Diet with 5.5% soy oil. Data for a DM basis. Source for C: Batal and Parsons [16]. Diet with 5.5% soy oil. Data for DM basis. Source for D: Zelenka [22]. Diets with no added fat. Data on DM basis are adapted from original work. The only difference between Experiments (EXP.) 1 and 2 was that the particle size of the corn used in Experiment 1 was coarser (less than 1 mm vs. less than 0.42 mm in diameter, respectively). proves the ME n by 1.5 to 3%, which is primarily due to an improvement in fatty acid digestibility, whereas others have found no effects [36, 40]. In fact, there is some commercial evidence that HP of barley and wheat diets causes an increase of enteric problems associated with wet litter and that the use of appropriate enzymes reduce the condition [41]. NSP AND ENZYMES The most important factor that controls microbial fermentation in the GIT is the amount and type of substrate available for the microbiota. It is widely accepted that the fibrous components of feedstuffs have a negative effect on energy and protein digestibility, which eventually will jeopardize feed efficiency and growth. As a consequence, current practical diets for prestarter feeds are based on corn, wheat, and high-protein soybean meal, with limited fiber. However, the term crude fiber is poorly defined and includes a large number of compounds with properties that differ greatly. There are suggestions that certain amounts of appropriate fiber sources could help in the prevention of digestive disturbances and contributes to the adaptation of the GIT to practical production systems [42, 43]. In fact, rats fed a fiber-free diet maintain an immature finger-shaped villus pattern, whereas rats fed diets rich in fiber develop mature mucosal structure [23]. Proventricular hypertrophy and dilatation and poor gizzard development have also been linked to low-fiber diets [44] and to small fiber particles [45]. Certain components of fibrous feeds could supply fermentative substrates to the flora of the large intestine and, most importantly, promote physiological and functional development of the GIT, thereby reducing the incidence of enteric problems. It could be of interest to study the inclusion of well-defined sources of fiber in the prestarter feed on villus development, functioning of the proventriculus and the gizzard, and late growth. Nonstarch polysaccharides, especially the soluble fraction, have been recognized as antinutritive factors in poultry with negative impacts on digestion and absorption of starch, protein, and primarily lipids. The mechanisms by which NSP reduces broiler performance are not well understood but NSP may 1) increase endogenous losses (secretions, mucus, enzymes, and sloughed cells); 2) increase viscosity, reducing mixing and contact of enzymes and nutrients; 3) enclose nutrients into the cell walls, limiting the access of enzymes; 4) change microbial activities with potential toxin production; and 5) alter the morphology of the GIT. Soluble NSP are highly fermentable, increase digesta viscosity, and decrease the rate of diffusion of substrates and digestive enzymes in monogastrics, effects that are all detrimental to healthy development of the microbiota [42, 46]. Also, NSP present in the protective matrix of the kernels reduce the accessibility of enzymes to starch granules and have detrimental effects on starch digestibility. Heat processing increases the solubility of NSP, especially in the case of β-glucans [37], which may compromise chick productivity. As a consequence, the addition of exogenous enzymes, such as β-glucanases and xylanases

9 MATEOS ET AL: INFORMAL NUTRITION SYMPOSIUM 445 TABLE 9. Influence of heat processing and enzyme supplementation on cornstarch fecal digestibility (%) A Broiler age B (d) Heat processing Average Raw 94.2 b 94.9 b 95.7 b b Cooked C 95.8 a 96.7 a 96.7 a a Enzymes D ppm a,b Means within a column with no common superscript differ significantly (P < 0.05). A Source: Gracia et al. (2003a) [8]. B Age effect (P < 0.001). C Processed at 99 C for 50 min followed by rolling. D Protease, xylanase, and α-amylase complex (Danisco Ingredients, Brabrand, Denmark). may yield beneficial results for starch digestibility, especially when heat is applied to ingredients or diets. Enzymes that improve the use of grains rich in NSP have made a major contribution to reduced feed costs in many areas of the world where viscous cereals are the major source of energy. Enzymes are substrate-dependent and may improve bird performance by increasing nutrient digestibility or by augmenting feed intake. Lázaro et al. [47, 48] have indicated that the beneficial effects of ES in laying hen diets are mostly due to an improvement in nutrient digestibility, whereas for broilers feed intake is also important. Enzymes are most effective in broilers fed ad libitum with viscous heat-processed cereal diets rich in saturated fats [39, 41]. The effects of ES on digestive and productive traits are more evident for barley than for wheat diets and are almost negligible for diets based on cereals with low-nsp content. Mahagna et al. [6] have observed that addition of exogenous amylase and protease to a sorghum diet reduced small intestine weights at 7 and 14 d but had no effect on the digestibility of nutrients in broilers. Fat is the nutrient most benefited by ES [8, 24], although digestibility improvements of up to 8% for starch and 19% for nitrogen have been reported with ES in barley diets [33]. Nissinen et al. [41] conducted a trial in which pelleted or expanded and pelleted wheat diets were supplied to broilers with or without ES. Expansion of the diet increased chyme viscosity from 6.9 to 20.0 cp, but ES reduced viscosity to 3.8 cp. Feed conversion from 7 to 28 d was impaired by expansion in the absence of enzymes, but efficiency was recovered when enzymes were added to the expanded wheat diet (1.50 a, 1.47 ab, 1.53 a, and 1.39 b for pelleted diets without or with ES and for pelleted and expanded diets without or with ES, respectively; P < 0.01). Data of Gracia et al. [8] working with broilers fed a corn-soybean meal diet are shown in Table 9. Starch digestibility increased with age and HP of the corn but not with enzymes. Also, no interaction (HP ES) was observed for starch digestibility. In a recent experiment [49], the influence of HP of barley (cooked at 99 C for 50 min) and ES (β-glucanase and xylanase complex from GNC Bioferm, Saskatoon, Canada) on broiler performance at 42 d was studied (Table 10). Heat processing of barley improved daily gains at 7 d but the effects disappeared thereafter. Enzymes improved performance at all ages but no interaction (HP ES) was detected for any trait. Available information indicates that use of adequate combinations of enzymes improves nutrient digestibility and poultry performance most of the time. The beneficial effects are more pronounced in broilers fed viscous grain diets. Also, enzymes are more effective in heat-processed diets such as expanded feeds or when heated cereals are used. An absence of efficacious enzymes focused on the degradation of oligosaccharides is noticed in the marketplace. The research and development of oligosaccharidases is warranted because of the high use of soybean meal and other legumes, the potential effects of their supplementation on reduction of intestinal viscosity, and improvement of nutrient digestibility and bird performance.

10 446 JAPR: Symposium TABLE 10. Influence of barley processing and enzyme supplementation on performance of broilers A 0 7 d 0 42 d Item ADG (g) FC (g/g) ADG (g) FC (g/g) Enzymes B ppm Heat processing Raw Heated C SEM Probabilities Main effects Enzymes Heat processing NS NS NS A Source: García [49]. B Xylanase and β-glucanase complex from Aspergillus niger (GNC Bioferm, Saskatoon, Canada). C Average value for micronized and expanded barley. NS P > PARTICLE SIZE, FEED FORM, AND WHOLE GRAINS Physical structure of the feed (wet feeding, particle size, feed form, and inclusion of whole grains) influences nutrient digestibility, composition of the microflora, and feed intake. Wet mash has commonly been given to backyard chickens but is not used in intensive production systems because of management problems. Forbes and Yalda [50] indicate that wet feeding results in a significant reduction in intestinal mucosal cell proliferation in broilers, which contributes to a marked advantage in feed efficiency (17% improvement) and daily gain (27% improvement). Fine grinding of feedstuffs is a common practice in broiler feeds because small particle size improves nutrient digestibility and pelleting of feeds [51, 52, 53]. However, finely ground cereals and pelleting of the feeds might be detrimental for mucosal cell growth and functionality of the digestive tract [54]. Fine particles produce atrophy of the gizzard, a major regulator of intestinal motility [55, 56], enzyme secretion, and also modulate the development of the gastrointestinal flora. Additionally, atrophy of the gizzard is accompanied by an increase in the ph of the contents, which reduces microbial control and might affect appetite and performance [56]. Healy et al. [57] observed that gizzard weights of broilers fed diets based on ground corn with a particle size of 300 µm were 20.9 g/kg BW, whereas for broilers fed corn with a particle size of 900 µm gizzards were 24.4 g/kg BW. Nir et al. [56] theorized that large particles are better suited to the intestinal tract of the chick because they stimulate peristalsis more than small size particles do. In the avian species, reflux of the intestinal contents is common and acts as an adaptation to their short intestine. Large fiber particles enhance digesta motility and backflow within the gastrointestinal tract, which in turn may allow better utilization of nutrients [45]. With finely ground particles, reflux of the gastric content is not effective, and certain amounts of protein pass undigested to the hindgut, compromising the equilibrium of the microflora. Also, the presence of fine feed particle sizes, especially in the case of wheat diets, causes an agglomeration of pasty material on the beak, an increase in water consumption, and a reduction in feed intake [58]. Trials conducted worldwide have shown that broilers fed mash diets had lower mortality rates than broilers fed pellets. Bennett [59] indicates that the slower growth rate together with larger particle size of mash feed, as compared to pellet feed, helps to improve bird health. A survey conducted with commercial flocks in Canada [59] revealed that mash-fed birds averaged 5.0% total mortality compared to 6.6% in pellet fed flocks, although most of the differ-

11 MATEOS ET AL: INFORMAL NUTRITION SYMPOSIUM 447 ence was due to acute death syndrome (1.9 vs. 2.8%, respectively). Feeding whole grains to poultry has been a common practice worldwide for the last 50 yr. In fact, many integrated poultry companies in Denmark, the United Kingdom, The Netherlands, and other countries are diluting broiler rations with up to 25% whole wheat. The general claim is that feed processing and diet costs are reduced when feeding whole grains to broilers and turkeys [60]. Plavnik et al. [61] compared the use of 20% ground or whole wheat in diets for broilers. Whole wheat improved body weights (2,494 vs. 2,431 g; P < 0.05) and feed conversion (1.82 vs g/g; P < 0.05) at 7 wk and increased gizzard weight (16.5 vs g/kg BW; P < 0.05). No differences were observed for percentage of abdominal fat. In a second trial, the inclusion of 15% of whole wheat in the diet gave similar results to the first trial, although in this case, body weights were not affected by diet (2,737 vs. 2,718 g for control and whole-wheat inclusion diets, respectively; P > 0.05). Most studies have focused on the benefits of grain inclusion in the diet on gizzard functioning, which may result in reduced incidence of coccidiosis and other enteric diseases [59, 62] and improved feed efficiency [59, 61]. Svihus et al. [63] observed that digesta from chickens fed whole grains had similar particle sizes of the contents in the duodenum than digesta from chickens fed ground grain, indicating that feeding of whole grains stimulates gizzard development. Also, a significant decrease in gizzard ph and an increase in amylase production have been observed with feeding of whole cereals, which may help to reduce the risk of pathogens entering the GIT and improve starch digestibility. Svihus et al. [64] observed that replacement of ground wheat with whole wheat increased fecal (96 to 99%) and ileal (93 to 99%) starch digestibility. Therefore, whole-grain feeding may improve bird performance by increasing gizzard activity, which in turn will enhance enzyme production in the GIT and the health status of the bird. It has been reported that whole-grain feeding reduces water intake and improves litter condition [59, 65], which in turn may reduce the incidence of leg abnormalities [65]. Also, unprocessed wheat has a high endogenous phytase content, which may help to reduce the need for additional mineral phosphate or ES. The main disadvantages of whole-grain feeding are the reduction in the quality of feed mixing and lack of uniformity of the flock. Also, whole-grain feeding requires a longer feed withdrawal prior to slaughter to allow for the complete emptying of the GIT. Some authors indicate that the use of high percentages of whole grains in the diet might reduce weight gains, carcass yields, and the percentage of breast meat at the expense of abdominal fat, especially when offered free choice [66, 67]. The main reason of these observations could be an alteration of the balance between amino acids and energy of the diet since cereals are poor sources of protein. NUTRITION AND IMMUNITY Birds at hatch have an immature immune system and are very susceptible to certain enteric disorders associated with exposure to pathogens [4]. Delaying access to feed and water results in a reduction in the rate of absorption of amino acids and other nutrients in the small intestine and may reduce the ability to produce antibodies against diseases [68]. Piquer et al. [69] observed that the GIT serves as an important barrier between the external environment and the interior of the body and that the concentration of IgA of intestinal tissue of poults was very low at 1 d posthatching and increased slowly through Day 9. Dibner et al. [68] also observed the absence of IgA at hatching but indicates that early feeding favors the appearance of biliary IgA, thereby increasing the capability of the chick to respond to vaccines. In addition, these authors indicate that early feeding is associated with greater bursa weights and greater lymphocyte proliferation. Summers [70] found that the GIT in the broiler chick is the major site of nutrient uptake accounting for 23 to 36% of whole-body energy use and 23 to 38% of whole-body protein synthesis. Changes in GIT conditions due to disease have a significant impact on the efficiency and requirements for energy and protein of the chick. Any bacterial challenge to the GIT is accompanied by an inflammatory process.

12 448 Obled [71] indicated that the metabolic disturbances that accompany a bacterial challenge redirect nutrients from physiological processes important for growth towards host defense. Potential limiting amino acids for protein synthesis in the immune system are unknown, but, clearly, lysine is not limiting [72]. There is evidence in humans and in pigs, that luminal glutamine benefits normal mucosal permeability in states of enteric infection [71, 73]. Glutamine is important for the production of hexosamines used for the synthesis of mucins and glycoproteins and could play a role in the maintenance of the passive barrier to bacterial ingress. Glutamine is also used for gluconeogenesis and as an energy source, being a major fuel for the intestinal mucose and immune cells [71, 74]. Besides, amide nitrogen is used in the synthesis of nucleotides, and therefore the requirement for glutamine of rapidly proliferating cells, such as those of the immune system and intestinal mucose, is high [75]. Moreover, the oxidation rate of most amino acids increases during inflammatory states, which increases the needs for intracellular antioxidants such as glutathione, which requires cysteine and glutamine for its synthesis [71]. Therefore, activation of the immune system would cause enhanced glutamine consumption and will also increase the need for other selected amino acids. Rowlands and Gardiner [76] have suggested that substrates capable of enhancing intestinal integrity and supporting immune function in humans include amino acids (glutamine, arginine, and ornithine), fatty acids (short chain and n-3 fatty acids), and nucleotides (DNA). Whether an extra exogenous supply of these nutrients will enhance the mucosal barrier and support immune function in the bird is not known at the present. NE AND OTHER ENTERIC DISORDERS Intestinal disorders are a major concern for the poultry industry in the EU-15 countries and there is strong evidence that they are the main consequences of the banning of growth promoters [77]. Clostridium perfringens-associated NE is a perennial problem among rapidly-growing broiler strains that are raised intensively in modern microenvironments. Necrotic enteritis JAPR: Symposium is an acute, infectious, noncontagious disease that affects the intestinal lining of the digestive tract in chicks from 2 wk to 6 mo of age. The causal agent is Clostridium perfringens, a spore-forming, rod-shaped, obligate anaerobe that is a normal inhabitant of the ceca but is absent from the small intestine of healthy birds. The most commonly reported signs of NE are intestinal inflammation, diarrhea, increased water intake, wet litter, and mortality. The organism has also been associated with other poultry problems such us gizzard erosions and liver abnormalities [78]. Factors that predispose flocks to NE include management stress, subclinical intestinal coccidiosis, abrupt changes in dietary formulation, alteration of the feeding program, and the use of specific diets [77, 78, 79]. Historically, in-feed antibiotics have been used for the treatment and prevention of NE, but this is no longer an option in many developed countries [80]. Diet composition has been reported to have a marked effect on the flora that develop in the alimentary tract of the chick and in the subsequent C. perfringens numbers. Kaldhusdal [77] indicated that selection of optimal feed ingredients might represent an alternative to the control of Clostridium perfringens-associated disease conditions in the absence of feed antibiotics. He observed that the inclusion of 20% corn in diets for broilers contributes to the prevention of the disease and that the use of exogenous carbohydrases also reduces the occurrence of intestinal and hepatic problems related to Clostridium. Additionally, dietary lactose reduced intestinal counts of clostridia, whereas sucrose, glucose, and fructose were associated with an increase at the intestinal level [77, 81]. Bedford [82] proposed that proliferation of Clostridium perfringens and development of NE is facilitated by the appearance of large quantities of dietary protein in the ceca. Undigested protein that accumulates in the hindgut because of excess in the diet or the use of protein sources of low digestibility may increase the problems associated with NE. With viscous diets or in the presence of subclinical coccidiosis, even greater quantities of nitrogen will escape digestion and enter the ceca, resulting in more frequent occurrences of NE [81, 83]. However, data on recommended sources of pro-

13 MATEOS ET AL: INFORMAL NUTRITION SYMPOSIUM 449 tein in the diet to reduce the incidence of the disease are conflicting. Thomke and Elwinger [84] indicated that animal proteins give rise to more digestive problems than vegetable proteins. In fact, fishmeal has been used in diets for poultry to induce infection by Clostridium perfringens [85]. However, a common practice in the field, when any type of enteritis affects a flock, is to include fishmeal in the diet to reduce the quantity of soybean meal used [86]. When the incidence of NE and other enteric disorders is high, it is wise to reduce the level of protein in the diet and to increase the use of synthetic amino acids. In general, broilers fed wheat or other high- NSP grains are more susceptible to NE than broilers fed corn [77, 81], but the reasons have not been determined. One explanation is that the carbohydrates in corn may be less available to microbial digestion than the carbohydates in wheat. Untawale and McGinnis [87] observed that diets based on rye depress chick growth and increase the number of bacteria adhering to the lower part of the intestine, an effect that was suggested to be related to the high content of complex carbohydrates of rye [88]. Riddell and Kong [81] observed that mortality due to NE was higher among chicks fed wheat, rye, barley, and oat groats than among chickens fed corn diets. However, the addition of pentosanases to the wheat diet did not affect mortality due to NE. Moreover, inclusion of whole grains reduces wet litter problems and associated enteritis in chicks fed diets without in-feed antibiotics [77]. Therefore, factors other than NSP present in viscous grains are responsible for the increase in Clostridium counts observed in the GIT of birds fed wheat. For example, Nir et al. [56] observed that gizzard weight was greater in broilers fed corn than in broilers fed wheat. Also, litter consumption has been suggested to result in minor intestinal damage, which in the presence of Clostridium perfringens may cause NE. Branton et al. [89] observed that the consumption of pine shavings, pectins, or guar gum increased the number of necrotic lesions in the intestine of the bird but failed to yield lesion scores as high as that from the wheat-based diet. Further studies are needed to investigate the influence of different dietary fiber sources on intestinal digesta movement and the occurrence of NE and other enteric diseases. Enteric diseases in poultry are complex and are affected by many dietary and nondietary factors, such as subclinical diseases, stresses, lack of hygiene, and immunodepression. Alternative methods to control pathogens causing enteritis include modifying management practices to limit exposure to pathogens and to minimize stress (density, hygiene, chick quality, house heating, ventilation, and vaccination programs for target diseases) and undertaking selective breeding for resistance to infectious diseases. But nutritional management of the GIT and modifications of the characteristics of feeds may ameliorate the symptoms. Coarse grinding (>4 mm), mash feeds, low-protein diets (undigested portion), reduced levels of ground wheat, enzymes, and inclusion of whole grains are some of the solutions proposed. In addition, inclusion of essential fatty acids, emulsifiers, probiotics, and prebiotics, as well as immune enhancers, is also recommended. An area of considerable interest is the control and reduction of antinutritional factors present in the diet, including mycotoxins, lectins, and trypsin inhibitors. More than 25% of current diets for poultry consist of soybean products in spite of the fact that birds do not use the oligosaccharide fraction of the meal well. The amount of soy products currently used in Europe for poultry has increased because of the restrictions imposed on the use of protein of animal origin. It is not uncommon, especially in turkey feeds, to find diets with more than 40% soy products. Soybeans are processed the same today as they were 60 yr ago, and no methods are in use to remove the oligosaccharides present in the meal for poultry diets. Another problem to be addressed is the high use of full-fat soybeans in diets and the lack of adequate control of the presence of antinutritional factors, especially antiproteases. Most nutritionists accept 6 to 8 mg/kg of trypsin inhibitors in treated soybeans. However, Clarke and Wiseman [90] have indicated that for modern commercial poultry production, the level should be reduced to less than 4 mg/kg.