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发表于 2007-6-10 12:17:06
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Feeding whole grains to poultry improves gut health
Feeding whole grains to poultry improves gut health
By PETER FERKET
Dr. Peter R. Ferket is an extension poultry nutritionist at North Carolina State University, Raleigh.
Feeding whole grains along with pellet-processed feed could result in considerable feed cost savings, depending upon the production system and market conditions. Moreover, some health benefits could be realized if a proper portion of the bird's diet contained whole grains.
During the past 50 years, considerable change has occurred in the manufacturing of commercial poultry feeds. In the very early days of commercial poultry production, poultry were fed diets that included whole grains and protein concentrates, often offered as a free-choice, cafeteria-style feeding program. Beginning in the 1950s, many poultry producers began feeding complete diets in mash form. Young birds were fed a finely ground mash feed, and a coarser grind was fed to older birds. This practice continues today, especially for laying hens. During the 1970s, many commercial feed mills began pellet processing poultry feeds, and today, essentially all commercial broiler and turkey feeds are pellet processed in some form.
Pelleted feeds became an obvious advantage because of improved feed conversion, better feed handling and transport characteristics and reduced ingredient separation. Feed manufacturing continues to evolve from an art into a science as operations are modified to increase pelleting rate and improve pellet quality.
Recent advances in pelleting include "high-temperature, short-time" and "expansion" conditioning. The pressure and heat from the steam and friction in the expander increases starch gelatinization, denatures proteins, deactivates some antinutritional factors and destroys pathogenic and spoilage microorganisms. These advances have improved pellet production efficiency and pellet quality, which is usually measured by the pellet durability index.
Major concerns of high-temperature conditioning by expansion prior to pelleting are the destruction of nutrients, particularly enzymes, vitamins, amino acids and direct-fed microbials. Increased dietary fortification or post-pellet applications of critical nutrients can address these concerns. However, highly processed feeds that are finely ground, heat-processed and highly digestible may predispose poultry to enteric motility problems.
It is true that the more physical work feed manufactures put into processing feed, the less work poultry must devote to prepare a diet for digestion and, thereby, improve feed conversion efficiency. When feed manufacturers do too much physical work in physical feed processing, which leaves little for the bird to do, enteric dysfunction in the birds will likely occur. To maintain normal gut motility and digestion in poultry, a portion of the diet may need to be in an unprocessed or "pristine" state. After all, these birds are designed to be seed-eaters with a powerful grinding organ, the gizzard. Highly processed feeds may negate the need for normal gizzard function, which may predispose poultry to such common problems as feed passage, flushing, enteritis, proventriculitis, litter and feather picking or a perturbation of gut microflora.
The objective of this article is to discuss: (1) dietary factors that influence gut motility; (2) normal gut motility function in poultry, and (3) a practical approach to facilitate normal gut motility in poultry by dietary inclusion of whole or coarsely ground grain.
Dietary modifiers of gut motility
Dietary fiber, fat and feed texture can modify gut motility. Feed passage rate generally increases as dietary fiber content increases. Conversely, passage rate decreases as dietary fat content increases. Proper dietary balance of these dietary components may help normalize gut motility in poultry exhibiting enteric problems. Good gut motility is necessary for proper food digestion, nutrient absorption and maintaining a healthy gut environment.
Textural properties of feed (fiber content, particle size and particle integrity) are important for proper gizzard musculature and motility. To illustrate this point, turkey poults were fed a highly processed feed (fine grind, expanded, pelletized and crumbled), but one group was reared in Farmer Automatic cages equipped with a trampoline perforated floor, and the other group was reared on soft pine shavings litter floor. Dissection of sample poults at four weeks of age revealed that those reared on the litter floor had a much larger and muscular gizzard and a smaller, well-defined proventriculus compared to poults reared in the cages (Table 1). This response was apparently associated with the consumption of pine shavings by the poults reared on the litter floors because those in cages did not have access to shavings. Why did the poults consume pine shavings even though it has no apparent nutritional value? A desire to satiate the gizzard and normalize gut motility may be the answer to this question.
Gut motility, implications
The gizzard is the "pace-maker" of normal gut motility (Duke, 1994). Unlike mammals, vigorous gut refluxes (reverse peristalsis) are normal in birds as an adaptation to compensate for a short intestine. The refluxes serve to re-expose intestinal digesta to gastric secretions, vigorously mix digesta with enzymes to enhance digestion, enhance nutrient absorption over a short segment of the gut and discourage microbial proliferation that may cause disease or compete for nutrients. Dietary fat stimulates the reflux of digesta from the jejunum through duodenum into the gizzard, thus slowing food passage rate and improving the utilization of dietary protein and energy.
Reverse peristalsis in poultry occurs in three distinct regions in the gut: (1) the gastric reflux, (2) the small intestine reflux and (3) the cloaca-ceca reflux. The phenomenon of gut refluxes is a creative adaptation in birds to minimize gut mass without compromising digestive efficiency.
The first gut reflux moves digesta from the gizzard back into the proventriculus once for each gastro-duodenal contraction cycle.
The gizzard, the food-grinding organ, consists of two thin and thick pairs of muscles, which contract alternately to mix (thin pair) and grind (thick pair) the gastric contents. In addition, the motility of the proventriculus and duodenum is coordinated with that of the gizzard. A normal gastroduodenal contraction sequence follows: "thin pair -- duodenal contraction -- thick pair -- proventricular contraction." The gastro-duodenal contraction sequence appears to be coordinated by nerves within the gastric region and to be initiated by a neural pace-setter near the pyloric valve of the gizzard. Chyme is moved sequentially from the gizzard back into the proventriculus, then forward into the gizzard and duodenum. This contraction cycle is repeated several times until the feed particles are reduced to a diameter of less than 1 mm and finally leaves the gizzard via the crevaces that convey material toward the duodenal sphincter.
Ingested feed is repeatedly ground and mixed in the gizzard, sent back to the proventriculus for more peptic juice application and returned to the gizzard. Thus, the gastric reflux is an essential part of both physical and chemical preparation before subsequent digestion in the small intestine. By reducing food particle size, surface area is increased to maximize exposure to digestive enzymes in the small intestine. Furthermore, repeated exposure to pepsin (an endopepidase) in the proventriculus and gizzard increases the efficiency of protein fragment digestion by trypsin and chymotrypsin (both exopeptidases) in the small intestine.
The second gut reflux moves chyme from the duodenum and jejunum back into the gastric area. This reflux occurs about three times per hour in poultry; however, it increases in rate as dietary fat increases and decreases in rate as dietary fiber increases. The characteristic yellow staining of the gizzard lining is evidence of bile exposure due to the reflux of intestinal chyme back into the gizzard. Bile may, in fact, be necessary to enhance the integrity of the kaolin matrix making up the gizzard lining. Inadequate bile exposure may result in excellerated gizzard erosion. Reverse peristalsis sufficiently increases food digestibility and nutrient absorption by slowing down overall passage rate through the gut and re-exposing intestinal digesta to digestive enzyme secretions.
The importance of feed integrity and vigorous gut motility on digestion is clearly illustrated by data reported by Rogel et al. (1987). These researchers demonstrated the inclusion of 10% (ground) oat hulls in a semipurified broiler diet containing either corn or raw potato starch. The presence of the oat hulls increased gizzard mass and also improved the digestibility of the potato starch, which is not readily digested by the amylase secreted in the bird's pancreas (Table 2). It is noteworthy that only whole oat hulls would elicit this response and not pulverized oat hulls or grit, thus emphasizing the importance of food particle integrity rather than a matter of dietary fiber content. Grit in the gizzard assists in food grinding but does not stimulate gizzard motility to grind food. In addition to improving digestive efficiency, periodic reverse peristalsis in the small intestine also helps maintain a healthy gut by discouraging colonization of pathogens and other organisms that compete with the bird for available nutrients.
The third and most unique reflux conveys chyme from the cloaca to the cecal touncils. This reflux is a continuous, low-amplitude, colonic antiperistalsis. Urine is conveyed from the urethral ports in the cloaca backward along the epithelial surface of the rectum and into the ceca, where microbial activity can convert uric acid into microbial biomass (Bjornhag, 1989; Karasawa, 1989). Additionally, the ceca are involved in water re-absorption facilitated by the absorption of volatile fatty acids producted by bacterial fermentation. Under normal circumstances, birds are very efficient at conserving body water. Of the total amount of water that is reabsorbed, 10-12% is absorbed in the ceca, 3-5% is reabsorbed in the rectum and the rest of the body water (about 85%) is reabsorbed by the kidneys.
Enteric disorders, such as diarrhea, swollen proventriculus, gizzard erosion and flushing, may partially be a consequence of dysfunctional gut motility associated with processed feed characteristics. The primary objective of modern feed manufacturing (grinding, post-mix grinding, steam conditioning, expansion and pelletizing) is to reduce the bird's "work" of feed prehension and enhance digestion for the sake of maximizing feed conversion efficiency. However, all this mechanical work invested into processing feed reduces the work load of the gizzard to grind the ingested food. In particular, highly processed feed leads to atrophy and malfunction of the gizzard, which then acts more as a transit organ rather than a grinding organ (Cumming, 1994).
Normal gastric reflux does not occur when birds consume highly processed feed, and, thus, proventricular hypertrophy occurs as an attempt to deliver sufficient peptic secretions within a single pass. Poor peptic digestion by pepsin in the gizzard will result in less efficient peptic digestion by trypsin and chymotrypsin in the duodenum. Consequently, more undigested protein ends up in the hindgut, where it is subject to microbial fermentation by putrefying bacteria, such as clostridia, campylobactor, listeria, pseudomonas, E. coli and other potentially pathogenic agents.
The literature has several examples that support the hypothesis that highly processed feed is associated with changes in gut morphology and increased health problems in poultry, despite improvements in feed conversion efficiency. Nir et al. (1995) and Munt et al. (1995) reported male broilers exhibited a threefold increase in mortality if they were fed pellets instead of a coarse mash. Moreover, the incidence of ascites may be affected negatively by dietary factors that improve feed conversion ratio, such as high-energy density and pelleted diets, all stimulating feed intake, protein accretion and oxygen consumption (Scheele, 1993). Riddell (1976) reported dietary fiber (in this study: oat hulls) added to pelletized feed reduced the incidence of dilated proventriculi of broilerchicks (Table 3). Concomitantly, the presence of structural fibres in feed stimulated normal development of the gizzard and proventriculus.
Whole wheat feeding
During a casual discussion with my father about six years ago, I mentioned my interest in solving enteric problems in poultry by dietary manipulation. "Based on my research" I said, "there is not a lot that can be added or done to a diet formulation to treat or reduce the susceptibility of poultry to gut problems such as flushing, diarrhea and feed passage." My father, who's career was livestock and poultry farming, looking at me with bewilderment, replied, "Don't you remember that when our hens became loose I told you to give them a little whole oats or whole wheat to tighten them up? I thought that was common knowledge because I learned that from my father." I had discredited this "old-timers" remedy after my years of academic study in poultry nutrition taught this practice as primitive and inefficient and seemed to favor more feed processing and use of feed additive antibiotics. However, my opinion about whole-grain feeding to poultry changed during my sabbatical study leave in the Netherlands in 1996.
Blending some whole wheat along with pellet-processed feed has become a common practice in Europe. There was a revival of this practice because of economic reasons shortly after the ratification of the General Agreement on Tariffs & Trade. Poultry farmers traded with wheat producers the right to land apply litter for wheat. Poultry farmers could then economically dispose of their litter, and wheat farmers gained from an economically favorable alternative to selling their wheat products at lower world market prices. At first, feed manufacturers opposed this practice because it adversely affected their feed sales. In response, they sponsored research to prove that the practice of diluting their carefully formulated feed with 10-25% whole wheat would adversely affect growth performance of poultry. Through their research, they discovered that adding some whole wheat on top of their formulas at the farm did not reduce performance to the degree as expected by nutrient dilution. When whole wheat was included within a balance ration, growth performance and bird health often improved and economic return improved.
Van Middlekoop and Van Harn (1994) conducted two experiments in which whole wheat was added to pellet-processed feed either increased incrementally to levels of 10, 15 or 25% (Figure 1) or at a constant level (Figure 2). Regardless of how the whole wheat was delivered, whole wheat feeding did not adversely affect technical performance in broilers (Table 4). In contrast, a marginal improvement in feed conversion along with significant improvements in economic return were proportional to the amount of whole wheat included in the diet.
The results of feeding whole grains to turkeys are more variable than observed with broilers. Several field studies conducted in Germany concluded that growth performance of turkey toms was adversely affected by whole wheat feeding, although economic return favored the practice (Tuller and Velten, 1988 and 1992; Reiter et al., 1994). A field trial conducted in the Netherlands also demonstrated a clear economic benefit of feeding whole wheat (Rooijakkers, 1997). In this Dutch trial, turkeys were fed a standard starter diet until three weeks of age. Then, from four weeks to market age, 10% whole wheat was included in the diet, adding 5% additional wheat every week until the diet contained 50% wheat.
Based on a series of field trials in Italy, Melandri (1998) reported turkey hens and toms fed standard whole wheat or sorghum up to levels of 17% of the diet improved a production efficiency index (measured as [market weight x livability]/[days of age x feed:gain]) without adverse effects on total yield and breast meat yield. Melandri (1998) noted that economic return improved significantly as the level of whole grain increased in the diet. The incidence of coccidiosis did not change despite the dilution of coccidiostat in the diet by whole grain addition. Moreover, litter quality and bird activity were generally improved by inclusion of whole wheat or sorghum. Some of the benefits observed by gradually increasing whole wheat within a feed phase was alleviation of the adverse effects typically observed during feed changes.
Including whole grains as a component of a complete diet may not only improve gut motility, but it may also be an economical benefit simply because less feed must be processed. Turkey companies in Italy and in the midwestern U.S. have reduced the amount of feed that must be processed by about 25% simply by blending whole wheat or whole corn with a pelletized feed concentrate. Moreover, this practice improved the feed mill efficiency because this feeding program required fewer formulas and longer processing runs. Additional feed formulas could be delivered to the birds simply by adding more whole grain to a common concentrate.
More scientifically designed experiments must be conducted before the feeding of whole grains to broilers and turkeys can be advocated as a standard practice. However, I believe there is sufficient physiological merit and practical evidence that warrant serious consideration for American feed manufacturers and poultry production companies. Feeding whole grains along with pellet-processed feed could result in considerable feed cost savings, depending upon the production system and market conditions. Moreover, some health benefits could be realized if a proper portion of the bird's diet contained whole grains. These benefits may arise from reduced litter consumption, better gut motility and reduced aggression. |
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