Maintaining the structure of the digestive tract in good health is critical for successful rearing of broilers. Dietary factors disrupting mucosal integrity or motility of the gastrointestinal tract (GIT) might induce enteric disorders, wet litter problems, poor pigmentation and inefficient growth. Enteric disorders have been managed through dietary changes including the use of in-feed growth promoters and animal proteins. Addition of certain antibiotics to feed at low levels is a common practice in poultry production and has been shown to improve weight gain and feed efficiency in the range of 1 to 5% (Thomke and Elwinger, 1998a). The reasons for the improvement are not well understood but some intestinal organisms such as clostridia and other grampositive germs are inhibited by these antibacterial agents. In fact, the restrictions imposed on the use of in-feed antibiotics and proteins of animal origin in many European countries have increased the incidence of clostridiosis and other enteric diseases; and the cost of broiler meat production has increased by around 0.01 €/kg (Mateos et al., 2001a; Van der Eijk, 2002). However, consumer concerns about recycling animal proteins and cross-resistance related to the use of additives requires new methods to protect enteric health and improve broiler performance.
Many poultry integrators in Europe are producing feeds without growth promoters, based exclusively on vegetable feedstuffs. Under these circumstances, problems related to necrotic enteritis (NE), feed passage, and overgrowth of intestinal microflora are frequently reported. Numerous natural products, including organic acids, probiotics, prebiotics, plant extracts, and immune stimulants have been proposed for the control of pathogens in the GIT (Flickinger, 2003; Hooge, 2003; Chaveeraach et al., 2004). Also, manipulation of the composition and nutrient content of the diet might help to improve GIT health. Options to minimize enteric diseases associated with microflora changes include the use of highly digestible feeds to improve the structure of the gut, adequate processing of raw materials and diets, and the use of exogenous enzymes, organic acids, yeasts, and other additives (Lilburn, 1998; Mateos et al., 2002). However, data supporting the effectiveness of these techniques are equivocal, and changes in flock management, early detection of symptoms of diseases, and careful design of the feeding program are required to reduce the incidence of enteric problems.
Post-hatch nutrition, feed managementand chick productivity
Growth of broilers during the first days post-hatch is of paramount importance for ultimate performance of poultry reared for meat. During the first week of life allometric growth is maximal and the chick multiplies initial body weight 4 to 5-fold. In commercial operations a large proportion of chicks remain without feed for more than 36 hrs after removal from the incubator as placement on the farm is frequently delayed because of hatchery processing and transportation. Furthermore, the yolk sac at hatch contains less than 1 g of triglycerides and is almost absent by the third to fourth day of life (Murakami et al., 1988; Bigot et al., 2003).
Therefore, residual triglycerides in the yolk sac are not a good reservoir of nutrients and early access to feed is critical for the newborn chick (Lilburn, 1998). Early access to feed and water stimulates the growth of the GIT and its absorptive capacity and improves gut integrity and subsequent performance (Moran, 1990; Noy and Sklan, 1999; Corless and Sell, 1999). The GIT adapts to the nature of the digestive contents, a response that is modulated by the health status of the gut. In case of disturbances, physiological responses take place with overgrowth of pathogenic bacteria and a reduction of the appetite. In practical conditions birds that eat more during the first week of life achieve the best final weights and feed conversion at slaughter (Martins, 2003).
The nutrient requirements of baby chicks and poults after hatching are not precisely known. Lilburn (1998) proposes feeding highly digestible protein ingredients in combination with corn for the first 10 days of life to meet the energy and protein needs of young birds. Batal and Parsons (2002a) observed that the ME(n) value for chicks of corn diets based on soybean or rapeseed meal was very low at 2 and 4 days of age, but increased afterwards. However, the ME(n) of a dextrose-casein diet was high at 2 days and no further improvements were observed with age (Table 1). Sulistiyanto et al. (1999) also indicated that casein was better utilized than fish meal and soybean meal for chicks less than 10 days 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 fat sources. On the other hand, Noy and Sklan (2002) observed that baby chicks do not respond to high-fat starter diets; and Sklan (2003) indicated that lipoprotein production might limit fat use in very young broilers.
Table 1. Influence of age on the ME(n):GE ratio of diets for chicks(%).1,2
1Batal and Parsons (2002a).
2Soy oil was used as the main fat source of the diets.
a-cMeans within a column differ significantly (P<0.05).
w-zMeans within a row differ significantly (P<0.05).
Data from different institutions indicate that dietary composition of the prestarter feed and delay of access to feed influence chick productivity, but that the effects tend to disappear with age. For example, Aranibar (2001) and Aranibar et al. (2001) observed that changes in the nutrient content (crude protein, lysine and ME concentration) of the diet or in the major energy source used (fats with different fatty acid profile, starch, and sucrose) or delays in the access to feed for up to 48 hrs affected many digestive and productive parameters in chicks from 0 to 7 days of age but that the differences tended to disappear with age. These results agree with Noy and Sklan (2002), who used a series of diets during the first week of age in which the level of fat, protein, and cellulose varied widely and found differences in broiler performance at day 7 but not at day 18. In general, losses in performance incurred by chicks held without feed for 36 to 48 hrs are compensated by increasing the length of time required to reach market weight by a similar period of time. Therefore, at farm level, where age of the chicks is measured as days post-feeding and not post-hatching, only small differences in final performance will be found associated with a moderate delay of access to feed.
Digestibility of nutrients
The National Research Council (1994) assumes that digestibility of nutrients is independent of age, an assumption that is no longer accepted (Batal and Parsons, 2002a; Mateos et al., 2002). Digestion and absorption of nutrients early in life depends primarily on pancreatic enzyme activity (Nitsan et al., 1991a, b), but the pancreas is immature at hatch. As a consequence, dietary nutrients are poorly utilized during the first 10 days post-hatching. Gracia et al. (2003a) 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 4.1, 3.9, 8.1, 4.6, and 7.9 days of age, respectively (Table 2), data that compare well with information from Sell (1996). Batal and Parsons (2002a) found that the ME(n) and the apparent digestibility of starch, fat, and selected amino acids of a corn-soybean meal diet was low at 2 days and reached a plateau at 14 days of age (Table 3). Lilburn (1998) indicated that overall digestibility of lipids in chicks for the first 3 to 5 days of age varies from 69% to 80% with the higher values corresponding to unsaturated fats. Therefore, proper lipid sources can be used successfully in prestarter diets for poultry.
Starch digestibility is critical for understanding energy utilization because the starch content of a typical poultry diet ranges from 35 to 40%. It is believed that α-amylase is produced in excess of requirements (Moran, 1985; 1992), but several reports indicate that starch digestion at the end of the ileum of young birds is incomplete. Rogel et al. (1987) observed that in meal diets, fecal digestibility of wheat starch was 77.2% at 3 weeks and 97.8% at 6 weeks of age. Weurding et al. (2001) found that total tract digestibility of starch varied from 98.9% for tapioca pellets to 31.7% for raw potato starch, with intermediate values for cereals (93.8 to 98.3%) and legume grains (74.5 to 81.5%). Mateos et al. (2002) and Gracia et al. (2003a) observed that total tract digestibility of starch and ether extract in broilers increased with age in both corn- and barley-soybean meal diets (Table 4). Similar results have been reported by Yuste et al. (1991), Batal and Parsons (2002a, b) and Gracia et al. (2003b).
Enzyme accessibility to starch is determined by the viscosity of gut contents and the nature and structure of the starch granules. In general, starch in small granules is hydrolyzed more rapidly than starch in large granules. Also, starches with high amylose content are less susceptible to amylase attack than starches with low amylose content. Therefore, rice might be a candidate for prestarter diets for chicks because its starch is very accessible and mostly of type A (easily digested compact starch with no free space left for water), granule size is very small, the amylose content is lowest among cereals, and the grain has very low content of ß-glucans and xylans. A recent study conducted in our laboratory (González-Alvarado et al., unpublished) has confirmed the potential of rice as an energy source in prestarter feeds for broilers. In two different trials we studied the influence of the main cereal of the diet (60% corn vs 60% rice), processing of the cereal portion of the diet (raw vs cooked and rolled) and the inclusion of insoluble fiber sources (none vs 3% soy hulls vs 3% oat hulls) for broilers from 1 to 21 days of age. Rice feeding consistently improved feed conversion in both trials, but no differences between cereals were observed for feed intake or daily gain (Table 5). The data indicate that rice is well utilized by the chick and that its metabolizable energy content is approximately 3 to 5% higher than that of corn.
Table 2. Changes with age in relative weights of digestive organs of the chick (% BW).
1Gracia et al. (2003a).
P<0.001 with age (0, 4, 8, 15, 21 days).
Table 3. Influence of age on apparent fecal digestibility of nutrients in New Hampshire x Columbian male chicks.1,2
1Batal and Parsons (2002a).
2Diets with 5.5% added soy oil.
a-dMeans within a column with no common superscript differ significantly (P<0.05).
Table 4. Influence of age on starch and ether extract fecal digestibility in broilers (%).
1Mateos et al. (2002). Corn-soybean meal diet with 2.7% lard.
2Gracia et al. (2003a). Barley-soybean meal diet with 6% lard.
Starch: linear, P<0.001.
Ether extract: linear (P≤0.01) and quadratic; P<0.01.
Table 5. Influence of type of cereal in the diet on feed conversion (g of feed/g of gain) of broilers from 1 to 21 d of age1.
1González-Alvarado et al. (unpublished data). Diets based on 60% of raw or cooked cereal.
a-bMeans within a column (for each trial) with no common superscript differ significantly (P<0.05).
Heat processing of ingredients and diets
Heat is usually applied to pellet poultry feeds and also to inactivate thermolabile antinutritional factors contained in some raw materials such as soybeans. Recently, expanded feeds (110ºC to 120 ºC for 5 sec) have been introduced into the market because of beneficial effects on feed hygiene, nutrient digestibility, and broiler productivity (Fancher et al., 1996; Mateos and Lázaro, 2001). The information available on the influence of heat processing on digestive physiology and poultry performance is scarce and contradictory (García et al., 1998; Mateos et al., 2002). Heat processing disrupts feed structure, facilitating the access to nutrients by digestive enzymes. However, heat processing also shifts the site of starch digestion, facilitates Maillard reactions, and solubilizes part of the starch and of the NSP, increasing digesta viscosity. Plavnik and Sklan (1995) have found that dry extrusion or expansion of a corn diet improved the ME(n) by 1.5 to 3%, primarily due to an improvement in fatty acid digestibility but no effect was found by Vukic Vranjes et al. (1994).
Commercial information indicates that heat processing of barley and wheat diets increases the incidence of wet litter and that the judicious use of appropriate enzymes reduces the condition (Nissinen et al., 1993), data which are corroborated by our own results (Lázaro et al., 2003a, b, 2004). García et al. (1998) studied the influence of heat processing of barley (cooked at 99ºC for 50 min) and exogenous enzymes (ß-glucanase and xylanase) on broiler performance at 42 days (Table 6). Heat processing of barley improved daily gains at 7 days but the effects disappeared thereafter. Enzymes improved performance at all ages but no interaction of processing and enzymes was detected for any trait. Similar results have been obtained by Mateos et al. (2002), working with raw and cooked corn (Amandus Kahl, Reinbeck, Germany) diets (Table 7). In a recent trial, González-Alvarado et al. (unpublished) have studied the influence of including heat processed corn or rice in the diet on performance of broiler chicks. The diets contained 60% cereal either raw or cooked (90ºC for 50 min and then rolled). Heat processing had little effect on productivity at any age but improved feed conversion in diets based on rice, although not in diets based on corn (Table 8).
Particle size, feed form, and whole grains
The benefits of feed processing have long been recognized by the feed compound industry. Physical structure of the feed (wet feeding, particle size, feed form, and inclusion of whole grains) influences GIT structure, composition of the microflora, nutrient digestibility, and feed intake. Fine grinding of feedstuffs is a common practice because small particle size improves nutrient digestibility and facilitates the process of pelleting (Douglas et al., 1990; Lott et al., 1992; Kilburn and Edwards, 2001). However, finely ground cereals might be detrimental for mucosal cell growth and motility of the GIT. Fine particles produce atrophy of the gizzard, a major regulator of intestinal motility (Nir et al., 1994; Jones and Taylor, 2001). Nir et al. (1994) theorized that large particles enhance GIT motility and stimulate peristalsis and digesta backflow whereas finely ground particles reduce the reflux of the digestive contents, resulting in more nutrients passing undigested to the hindgut. In a recent study, Kilburn and Edwards (2004) have found that coarse soybean meal increases bone ash of broiler chicks, probably through an improvement in mineral utilization, and also improves growth and feed efficiency when used in semipurified diets.
Table 6. Influence of barley processing and enzyme supplementation on performance of broilers.1
1García et al. (1998).
2Xylanase and ß-glucanase complex from Aspergillus niger.
3Average value for micronized and expanded barley.
Table 7. Influence of heat processing, enzyme supplementation, and age on fecal starch digestibility of corn diets for broilers (%).1
1Mateos et al. (2002).
299ºC for 50 min followed by rolling.
3Protease, xylanase, and α-amylase complex.
a,bMeans in a column differ significantly (P<0.05).
Age effect (P<0.01).
Table 8. Influence of heat processing of the cereal portion of the diet on broiler performance from 0 to 21 d of age.1
1González-Alvarado et al. (unpublished data).
2Cooked (90ºC; 50 min) and rolled.
3Average daily gain, g.
4Feed intake per g of body weight gain.
Significant interaction: cereal x HP for ADG (P<0.001) and FC(P<0.05) from 0 to 4 days and for FC (P<0.05) from 0 to 21 days.
In commercial practice most diets for broilers and turkeys undergo some type of processing. It is widely accepted that pelleting enhances feed value by making more nutrients available for growth. Two areas of interest in this respect are the influence of pellet quality on feed intake by young poults and chicks and on performance of growing and finishing birds. Quality and characteristics of the pellets define the ingestion of prestarter feeds by chicks and poults (Picard et al., 2000). In fact, the industry has started to manufacture micropellets or small crumbles of uniform size to maximize intake and improve performance at early ages (Martins, 2003). It is widely accepted that pellet quality of corn-based diets for broilers should provide more than 60% to 65% intact pellets at feeder level to maximize bird performance. However, there is a clear trend toward increasing the energy concentration of diets for broilers and turkeys to maximize growth, which often results in the inclusion of higher levels of supplemental fat. Usually, an increase in the dietary fat level results in a reduction in pellet quality. Consequently, efforts to increase the energy intake of birds through fat supplementation may be partially offset by a reduction in pellet quality. Therefore, any addition of fat to the diet of broilers to improve performance must not compromise pellet quality. On the other hand, a problem frequently found in commercial operations when wheat is the main cereal of the diet is the excessive hardness of the pellets, which reduces feed intake and increase wastage by the bird.
Feeding whole grains to poultry has been a common practice in Europe for the last 50 years. In fact, some poultry integrators are diluting broiler rations with up to 25% whole wheat to reduce feed cost of poultry diets. Plavnik et al. (2002) observed that the inclusion of 20% whole wheat in diets for broilers improved body weights (2,494 vs 2,431 g; P<0.05) and feed conversion (1.82 vs 1.93 g/g; P<0.05) at 7 weeks and increased gizzard weight (16.5 vs 15.0 g/kg BW; P<0.05). Svihus et al. (1997) observed that duodenal digesta from chickens fed whole grain had similar particle size to digesta from chickens fed ground grain. In fact, Svihus et al. (2002) observed that replacement of ground wheat with whole wheat increased ileal starch digestibility (93% to 99%) indicating that whole grain feeding may improve bird performance by stimulating gizzard development and enhancing enzyme production.
Crude fiber, nonstarch polysaccharides, and enzymes
An excess of fiber in feeds might impair nutrient digestibility and feed efficiency. Dietary fiber often increases endogenous losses leading to a decrease in ileal digestibility of starch, protein, and lipids (Souffrant, 2001). As a consequence, current practical diets for prestarter feeds are based on low fiber ingredients such as corn, wheat, and high protein soybean meal. However, dietary fiber is a heterogenous class of components differing in structure and physiological properties. In general terms, soluble fiber increases intestinal transit time, delays gastric emptying, increases pancreatic secretion, and slows absorption, whereas insoluble fiber decreases transit time and enhances waterholding capacity (Montagne et al., 2003).
Recent data indicate that adequate type and quantity of fiber could reduce digestive disturbances and improve the adaptation of the GIT of monogastric animals to current production systems (Graham and Åman, 1991; Hetland and Svihus, 2001; Mateos et al., 2001b; Hetland et al., 2003; Sklan et al., 2003). For example, proventricular hypertrophy and poor gizzard development has been linked to the use of low fiber diets (Riddell, 1976). Montagne et al. (2003) indicate that, depending on nature and physiological factors, dietary fiber may improve gut health, or alternatively enhance gut perturbation and subsequent diarrhoea in young animals. Therefore, more studies are needed to find the maximum and minimum levels of dietary fiber to be included in diets for poultry, especially at young ages. In fact, the British Society of Animal Science has recently proposed a minimum of crude fiber and of neutral detergent fiber in diets for young pigs (BSAS, 2003) but no studies have been conducted with young birds.
We have studied the influence of including different sources of insoluble dietary fiber in diets for broiler chicks (González- Alvarado et al., unpublished). Two control diets consisting of 60% corn or rice (either raw or cooked) and soy protein concentrate were formulated. The experimental diets included 3% of either soy hulls or oat hulls at expense of an inert material. The inclusion of the fiber sources consistently improved broiler performance at 21 days of age (Table 9). In a second test, diets low in fiber (1.5% crude fiber and 3.6% NDF) based exclusively on rice and soybean protein concentrate were formulated. The test diets consisted of adding 3% oat hulls (a source of lignified insoluble fiber) or soy hulls (a source of non-lignified insoluble fiber) at expense of an inert material. The inclusion of the two sources of fiber to the rice-soy protein concentrate diet improved feed conversion at early stages of growth and improved average daily gain at 21 days of age (Table 10). The inclusion of either soy hulls or oat hulls to the low fiber diets increased relative gizzard weight (% BW) (1.786c vs 2.407a and 1.868b for control, oat hulls and soy hullsincluding diets; P<0.001) and relative total digestive weight (% BW) (10.23b vs 10.76a vs 10.76ab%; P<0.01). Also, soy hulls but not oat hulls increased intestinal viscosity at 21 days of age (3.38 vs 3.36 vs 3.76 cP for control, oat hulls, and soy hulls diets, respectively; P<0.05).
Table 9. Influence of fiber inclusion in the diet on performance of broilers.1
1Gonzalez-Alvarado et al. (unpublished data).
2Significance of contrast: none vs hull inclusion.
Table 10. Effects of adding fiber sources to a low fiber diet on broiler performance at 21 days.1
1Gonzalez-Alvarado et al. (unpublished data).
2Significance of contrast: none vs hull inclusion.
Enzymes reduce feed cost when viscous cereals are the major source of energy. Non-starch polysaccharides, specifically the soluble fraction, have a negative impact on digestion and absorption of nutrients in poultry. The mechanisms by which NSP reduce broiler performance are not well understood. Soluble NSP increase digesta viscosity and reduce the accessibility of enzymes to starch, protein, and lipids of the diet. Added enzymes improve bird performance by increasing nutrient digestibility and feed intake, and balancing intestinal fermentation. Lázaro et al. (2003a, b) have indicated that for laying hens the beneficial effects of supplementary enzymes are mostly due to improved nutrient digestibility, whereas in broilers an increase in feed intake is also important. Fat is usually the nutrient whose digestibility is most benefited by added enzymes, although improvements of up to 8% for starch and of 19% for nitrogen digestibility have been reported in barley diets (Hesselman and Åman, 1986).
The available information indicates that enzymes improve nutrient digestibility and poultry performance and that the beneficial effects are more pronounced in broilers fed viscous grain diets than in broilers fed corn-based diets. Also, enzymes are more effective when heat processed ingredients or diets such as expanded feeds are used. Information on oligosaccharidases is scarce; and research effort to increase its use in diets based on soybeans protein meals and legumes is warranted.
Nutrition, immunity and entericdisorders
Birds at hatch have an immature immune system and are susceptible to enteric disorders associated with exposure to pathogens (Bar-Shira et al., 2003). Changes in GIT conditions due to disease have a significant impact on the efficiency and requirements for nutrients in the chick, because bacterial challenges redirect nutrients from growth toward host defense (Obled, 2002). Potential limiting amino acids for immune protein synthesis are unknown, but lysine is probably not limiting (Klasing and Leshchinsky, 2000). Rowlands and Gardiner (1998) indicate that in humans, certain amino acids (glutamine, arginine, and ornithine), fatty acids (short chain and n-3 fatty acids), and nucleotides (DNA) might enhance intestinal integrity and support immune function. There is evidence in humans and pigs that luminal glutamine benefits mucosal permeability, is used for gluconeogenesis, and is a major fuel and building block for synthesis of nucleotides in rapidly proliferating cells, such as those of the immune system and intestinal mucosa (Wu, 1998; Obled, 2002). Whether an exogenous supply of these nutrients will enhance the mucosal barrier and support immune function in the bird is controversial at the present time.
Necrotic enteritis is an acute, infectious, noncontagious disease caused by the overgrowth of Clostridium perfringens that affects the lining of the digestive tract in chicks from 2 weeks to 6 months of age. Factors that precipitate outbreaks of the disease include management stress, subclinical coccidiosis and abrupt changes in dietary formulation. Historically, in-feed antibiotics have been used for the treatment and prevention of NE and there is strong evidence that banning antibiotics has contributed to an increase in incidence of the disease.
Diet has a marked effect on the development of the microflora in the alimentary tract of the chick. Two major dietary factors that predispose flocks to NE are the use of cereal grains that increase the viscosity of digesta and the high levels of crude protein in the diet (Drew et al., 2004). Kaldhusdal and Skjerve (1996) observed that the inclusion of corn in wheat or barley diets for broilers contributed to the prevention of the disease. In addition, dietary lactose reduced intestinal counts of clostridia while sucrose, glucose, and fructose were associated with an increase (Riddell and Kong, 1992). Bedford (2000) hypothesized that the proliferation of C. perfringens is facilitated by the presence of large quantities of dietary protein in the ceca. If this is the case, viscous diets will increase the quantities of nitrogen that escape digestion resulting in a more frequent occurrence of NE (Al Sheikhly and Al Saieg, 1980; Riddell and Kong, 1992). When the incidence of enteric disorders is high, an increase in the use of high quality fish meal and of synthetic amino acids, and a reduction of the protein content of the diet is recommended (Mateos et al., 2001).
In general, broilers fed wheat or other high NSP grains are more susceptible to NE than broilers fed corn (Ridell and Kong, 1992; Kaldhusdal and Skjerve, 1996). However, the addition of pentosanases to wheat diets did not affect mortality due to NE, which indicates that other factors are responsible for the increase in clostridia counts observed in the GIT of birds fed wheat. Further studies are needed to investigate the influence of different dietary fiber sources on GIT motility, intestinal digesta movements, and the occurrence of enteric diseases.
It has been proposed that the control of antinutritional factors present in the diet, including mycotoxins, lectins and trypsin inhibitors might help to reduce enteric disorders. The use of soybean meal and soy products has increased in Europe because of restrictions imposed on the utilization of animal proteins and more than 40% of soy products are frequently used in turkey diets. Yet, soybeans are processed the same way today as they were 60 years ago and no methods have been implemented to remove the oligosaccharides present in the meal. In addition, full-fat soybeans are being included at high levels in all-vegetable diets, with inadequate control of antinutritional factors in many cases. Many nutritionists accept concentrations of 6 to 8 mg/kg of trypsin inhibitor in treated soybeans. However, Clarke and Wiseman (2001) have indicated that this level should be reduced to less than 4 mg/kg in young animals. Van der Klis and Jansman (2002) have estimated that the presence of 5.7 mg of trypsin inhibitor per kg of diet in piglets increases the percentage of energy required for maintenance from 5.5 to 13.1% (Table 11).
Table 11. Estimated energy costs for synthesizing endogenous protein with graded levels of trypsin inhibitor activity in the pig.1
1Van der Klis and Jansman (2002).
2Trypsin inhibitor activity.
3Excreted ileal endogenous N (g/d).
4Total synthesised endogenous N (g/d).
5Energy costs of endogenous protein synthesis (KJ/d).
6Percentage of maintenance requirements.
Enteric diseases are complex and affected by many factors, such as subclinical coccidiosis, stresses, lack of hygiene, and immunodepression, but dietary changes that improve gut health and stimulate gizzard development and motility might help to overcome digestive upsets. Coarse grinding, mash feeds, low wheat and protein diets, enzyme supplementation, inclusion of whole grains and a minimum amount of a convenient fiber source are some of the solutions proposed in this respect. In addition, the inclusion of essential fatty acids, emulsifiers, organic acids probiotics, and prebiotics, as well as immune enhancers, is also recommended. Most of these techniques are not sufficiently refined at present and further research is needed. Adequate management in terms of preventive vaccination programs, reduction of stresses, and improvement of hygienic conditions, together with dietary changes minimize the incidence of enteric disorders in antibiotic-free fed flocks. Removal of in-feed antibiotics from feeds is likely to increase production costs moderately, mostly because of the increase of enteric disorders including NE, but efficient production is still feasible without antibiotic use.
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Authors: G.G. MATEOS1, J.M. GONZÁLEZ-ALVARADO2 and R. LÁZARO1
1 Departamento de Producción Animal, Universidad Politécnica de Madrid, Madrid, Spain
2 Departamento de Agrobiología. Universidad Autónoma de Tlaxcala, Tlaxcala, México