SALUD DEL TGI FUNCION PRINCIPAL DEL TGI Desde el punto de vista de la Nutrición Animal El aparato digestivo puede presentar múltiples variantes morfológicas; pero el proceso digestivo tiene el mismo proposito en todos los animales: CONVERTIR LOS GLÚCIDOS, LÍPIDOS Y PROTEÍNAS EN UNIDADES MAS SENCILLAS, POR MEDIO DE LOS MECANISMOS Y FACTORES INVOLUCRADOS EN LA DIGESTIÓN y ASEGURAR UNA EFICIENTE ABSORCION SALUD DEL TRACTO GASTRO INTESTINAL : TGI - DIGESTION (accion mecanica por masticacion, accion quimica por HCl, enzimas). - TRANSPORTE DE DIGESTA (contracciones peristalticas). - ABSORCION (transporte activo, pasivo,) nutrientes a la sangre). - SINTESIS (proteinas verdaderas, acidos grasos, carbohidratos, vitaminas). EXCRECION ( productos de desecho: por la bilis se excreta toxinas, microbios, etc y por el recto se excreta calcio, magnesio y fosforo) - IMPORTANCIA DE LA SALIVA FUNCIONES DE LA SALIVA : - SOLUBILIZACION de alimento seco - LUBRICACIÓN Liga el alimento formando bolo alimenticio. - ENZIMÁTICA (Amilasa). - BUFFER (Bicarbonato de Sodio) - HIGIENE Oral - ENFRIAMIENTO EVAPORATIVO de algunas especies animales. - CONTROL DE SECRECIÓN (volumen y tipo) dependiente de sistema nervioso central SECRECION DE SALIVA & AGUA Cantidad y composición de la saliva varia considerablemente entre especíes. Cantidad relacionada al nivel de actividad de masticar Cantidad de secreción: - PERROS minima (lubricacion, no enzimas). - OVEJAS 3-10 litros/d - CABALLO 10-12 litros/d - VACUNO 130-180 litros/d DIGESTION • • • Carbohidratos→ monosacaridos Proteinas→ peptidos pequeños y aminoacidos Lipidos→monogliceridos y acidos grasos Digestión de los carbohidratos: Amilasa salival (boca) amilasa pancreática (intestino delgado), disacaridasas(intestino delgado) Digestión de las grasas: Lipasa pancreática Requiere de la presencia de bilis. Digestión de Proteínas: Pepsina en el estómago. Endopeptidasas de origen pancreático y Exopeptidasas (carboxipeptidasa de origen pancreático DIGESTION EN VARIOS NIVELES DIGESTION INTESTINAL : Bilis hepática: sin fermentos emulsiona grasas rico en Na y K favorece el peristaltismo intestinal, rebaja la tensión superficial del quimo, favorece la hidrólisis, impide la proliferación de bacterias de la putrefacción y otros mcorg. Perjudiciales. Jugo entérico: Amilasas, Proteasas y Lipasas Jugo pancreática: Tripsina: Proteínas y péptidos en AA Amilasa: Almidón e H.C. en azúcares Lipasa: descompone grasas en a. grasos y glicerina. Máxima actividad con pH 8 DIGESTIÓN GÁSTRICA: Ac. Clorhídrico Pepsina: Proteínas = polipéptidos + péptidos + peptonas Cuajo o renina: en lactantes, coagulación para facilitar la digestión (nata, caseína y lactosa) y el suero: (lactosa, lactoalbúminas, NNP y sales minerales) Lipasa: Actividad limitada por el bajo pH: Ac. Grasos + Glicerina DIGESTION DE PROTEINAS proteína del alimento polipéptido diipéptido proteína indigestible aa disponibles masticación HCl pepsina tripsina quimiotripsina carboxipeptid. minopeptid. elastasas DESARROLLO DE ENZIMAS LECHON DESARROLLO DE ENZIMAS (unids/kg p.v. en intestino a los 10 días de edad) POLLOS DIGESTION EN CONEJOS Reingestión ALIMENTO ABSORCIÓN INTESTINO DELGADO RESIDUO NO DIGERIDO secreciones endógenas partículas finas CIEGO partículas gruesas AGV HECES DURAS HECES BLANDAS DIGESTION EN EQUINOS DIGESTION EN RUMIANTES Producción diaria de saliva: VACUNO: 150 l.; OVINO: 10 l. Microorganismos anaerobios CONTENIDO RUMINAL: en 3 Fases: - Inferior: líquida y finas partículas · Superior: más seca y partículas groseras · Agua: 850-930 g./Kg. MS FERMENTACIÓN DE ALIMENTO DIGESTIÓN QUÍMICA Y FÍSICA · Masticación: 40-50 veces Condiciones homeostáticas: pH: 5,5-6,5 (fosfato y bicarbonato de la saliva y rápida absorción de ácidos). Presión osmótica: próxima a la sangre (iones) · Tiempo de masticación: 8 h. Anaerobiosis: consumo rápido de oxígeno · Tiempo de rumia: 8 h. Temperatura: 38-42 ºC m.o. PRINCIPALES MICROORGANISMOS ANAEROBIOS DEL RUMEN : 1. BACTERIAS 109-1010 por ml. Más de 60 especies Número y proporción según dieta 2. PROTOZOOS 106 por ml. Mayor tamaño Ciliados - Grupos: ISOTRICHIDAE U HOLÓTRICOS · Isotricha y Dasytricha · Ovalados · No ingieren partículas ni celulosa OPHYOSCOLECIDAE U OLIGÓTRICOS · Entodinium, Diplodinium, Epidinium y Ophryuoscolex · Tamaño y forma variable · Ingieren partículas y celulosa QUE HACEN LOS m.o. Funciones de los m.o. : -digiere la fibra a AGV -fabrica proteina -fabrica vitamins K and B complex La funcion del rumen es alojar microorganismos, similar en conejos y caballos cuy, Syntetiza todas las vitaminas del C. B, excepto vitamin B12, que requiere Co para su sintesis Syntetiza todas las vitaminas del C. B, excepto vitamin B12, que requiere Co para su sintesis Produce amonio: Utilizado por los m.o. para formar AA´s, pueden absorver AA´s para formar proteinas, pero parcialmente, satisfacen las necesidades de proteinas por digerir algunos m.o. Esto ocurre en el abomaso e intestino delgado Microorganismos en estomago convierte celulas vegetales en energia utilizable. Celulosa es degradado por accion microbiana. Los Acidos Grasos Volatiles de Cadena Corta (AGVCC) Aportan con el 6080% de la energia dietaria de rumiantes (dependiendo de la dieta). Grandemente absorvidos desde el estomago en la circulacion portal hepatica. Pricipales SCFAs: › Propionato: utilizado por el higado (gluconeogenesis) › Acetato utilizado para energia y formar grasas › Butirato utilizado para energia RUMIACION Rumia Comprende un ciclo de actividad de 4 fases : la regurgitación de la ingesta seguida de una remasticación, reensalivación y nueva deglución. Esto logra disminuir el tamaño de partícula del alimento y aumentar la superficie para la fermentación microbiana. Ocurre principalmente cuando el animal descansa y no come. DIGESTION FERMENTATIVA (FERMENTACION) Todos los mamiferos tienen alguna capacidad fermentativa que les permite la utilizacion de la fibra ingerida. • La importancia comparativa de la fermentacion esta relacionada a la fraccion de la digesta total contenido en los compartamentos fermentativos del TGI i • Bacterias anaerobicas, protozoa y hongos producen enzymas que degradan la cellulosa, hemicellulosa y pectina Productos de la digestion fermentativa : › Acidos grasos de cadena corta (SCFAs), tambien llamados acidos grasos volatiles (VFAs) › Gas metano › CO2 › Amoniaco (NH3) FERMENTACION EN MONOGASTRICOS Limitada fermentación post gástrica (colon, recto y ciego) TIEMPO DE TRANSITO EN EL TGI Cantidad de tiempo que toma el material para viajar de una parte del intestino a otra. Cuando el material viaja a traves del intestino muy rapido, disminuye el tiempo de transito intestinal. Cuando el material viaja a traves del intestino lento, se incrementa el tiempo de transito intestinal. ESTRUCTURA: BASE DE LA ABSORCION The villi increase the surface area of the ileum for the absorption. The villi are finger like projections into the lumen of the gut. The villi increase the available surface area by ten times. The crypts contain the secretory cells of intestinal secretion. Mucosa is a mucus secreting membrane. The circular and longitudinal muscles combine to create the contractions known as peristalsis that maintains the movement of chyme along the alimentary canal. The serosa is a tough outer membrane composed of collagen. TRANSPORTE ACTIVO Active Transport : Glucose absorption and Amino acids absorption into the epithelial cells. •Active mean that the membrane protein 'pump' requires energy to function •The source of energy is ATP from respiration •This moves the molecules from low to high concentration against the concentration gradient •The energy causes a shape change in the protein that allows it to move the molecule to the other side of the membrane. PARTICULARIDADES DE LA ABSORCION Many substances in the diet are composed of small molecules that need little or no digestion. These include sugars, mineral ions, vitamins and water. These are absorbed by different transport mechanisms: •Cholesterol and the fat-soluble vitamins (A, D, E, K) are absorbed into the epithelial cells of the ileum by lipid diffusion •Mineral ions and water-soluble vitamins are absorbed by passive transport in the ileum •Dietary monosaccharides are absorbed by active transport in the ileum •Water is absorbed by osmosis in the ileum and colon. CLASIFICACION DE LOS ANIMALES POR SU INGESTA DE ALIMENTOS PREFERIDO 1. Monogastricos ó norumiantes 2. Rumiantes o: - Pre-gastrico fermentacion (craneal) - Post-gastrico fermentacion (caudal) FERMENTADORES PREGASTRICO Clases Rumiantes Especies Vacuno, oveja Ciervo, antilope, camello Norumiantes Mono colobine, hamster Kangaroo, hippo Habito dietario herbivoros q pastan herbivoros selectivos, incluyendo folivores and frugivores herbivores selectivos Herbivores selectivos y que pastan FERMENTADORES POSTGASTRICO Clases Especies Digestores cecal Capybara Conejo Rata, raton digestores colonicos Sacculados Unsacculated Elephant, caballo, zebra Monos del nuevo mundo cerdo, humano Panda Perro, gato habito dietario Pastan herbivores selectivos Omnivoros Pastan Folivoros Omnivoros Herbivoros Carnivoros FERMENTACION COMPARATIVA POR ESPECIES CAPACIDAD DIGESTIVA COMPARATIVA SALUD DEL TGI Integridad anatómica y fisiológica (Estructura y Función). Microbiota del TGI: parte integral de la salud del TGI e influencia el desarrollo de la microanatomia, ayuda a los procesos digestivo, estimula el desarrollo del sistema inmune entérico y puede proteger contra la invasión de patógenos. Sistema inmune mucosal: la mucosa intestinal tiene una función de barrera, pero también puede generar una respuesta inmune protectiva contra patógenos. El TGI alberga el mas grande numero de células inmunes en el cuerpo. Fotos de: Collet, S. University of Georgia - 2008 Tabla 2. Cantidad de bacterias (log CFU/g) en el tracto intestinal del pollo en diferentes edades. CRECIMIENTO ALOMETRICO Tabla 1: Ingredientes y problemas potenciales en dietas para pollos sobre la salud intestinal INTEGRIDAD DEL INTESTINO El TGI constituye una extensa superficie en la que se produce un CONTACTO ÍNTIMO entre el organismo y las substancias de la dieta, microorganismos, parásitos y toxinas exógenas. El intestino permite el PASO DE SUSTANCIAS a la circulación sistémica, pero al mismo tiempo EXCLUYE COMPUESTOS PATÓGENOS (Gaskins, 1997). El TGI tiene múltiples MECANISMOS DE DEFENSA inespecíficos e inmunológicos. Los mecanismos no específicos incluyen producción de ácidos gástricos, peristaltismo, capa mucosa, estrecha unión entre las células epiteliales, proteo lisis, resistencia contra la colonización por bacterias patógenas y el eje intestino hepático. La defensa inmunológica del intestino delgado incluye la PRODUCCIÓN DE INMUNOGLOBULINAS secretoras, células M y linfocitos (Madara et al. 1990; Walker y Owen, 1990; Deitch, 1993; Wang, 1995). Los INDICADORES comúnmente usados para evaluar la integridad intestinal son la longitud de las vellosidades, profundidad de las criptas y número de células caliciformes, permeabilidad transepitelial, actividad enzimática de la superficie ciliada, inflamación y crecimiento del animal. INTEGRIDAD INTESTINAL (I.I.) (Cervantes, Phibro Animal Health Corp. EUA, 2011) Desarrollo completo, macroscópico y microscópico, a la integridad ininterrumpida y al funcionamiento normal del tubo intestinal. La I.I. optima es, desde el nacimiento hasta el final del ciclo productivo, es esencial para obtener el MÁXIMO POTENCIAL GENÉTICO de crecimiento y utilización eficiente de los nutrientes del alimento en base a un TGI saludable, una altura máxima de la villi, maxima densidad de la villi y máxima área absortiva. Es necesario estimular un desarrollo temprano, integro y completo del aparato GTI, glándulas y órganos anexos para maximizar la digestión y absorción de nutrientes. integridad del intestino manteniendo su ESTRUCTURA Y FUNCIÓN o simplemente un intacto y sano intestino (Dr. Harish V. Dharne, head of Avitech’s). Higher villi in the jejunum (p<0.01) were seen when Bacillus subtilis-based probiotics were used compared to diets without this additive VD was higher when probiotics based on Bacillus subtilis were used together with prebiotics based on MOS, compared to the use of probiotics based on Bacillus sp alone. It was also higher in the birds fed the probiotics containing a bacterial pool compared to those containing only one culture (probiotic 1). The results suggest that, in order to obtain higher VD (consequently higher nutrient absorption area), it is necessary to use MOS-based saccharides when probiotics based in only one bacterial culture are used. On the other hand, they would be not necessary if the probiotics has many bacterial cultures, as observed for probiotic 2. IMPORTANCIA DE LA INTEGRIDAD INTESTINAL (I.I.) FACTORES QUE AFECTAN LA I.I. CAUSA MAS COMUNES DE LA MALA I.I. AGENTES ETIOLOGICOS MAS COMUNES DE LA ENTERITIS RECOMENDACIONES NUTRICIONALES Acceso rapido de agua y alimento de buena calidad, para favorecer el desarrollo y maduracion precoz del tubo intestinal . Verificacion diaria del consumo (agua y alimento) mediante la palpacion del buche. Uso de enzimas para mejorar digestibilidad y reducir la viscocidad de cereales con contenido alto de polisacaridos no almidonados. Verificacion y rechazo de materias primas para la fabricacion de alimentos contaminados con micotoxinas o aminas biogenicas. Evitar el uso de grasas rancias o no estabilizadas con antioxidantes o que no cumplan con los requisitos de calidad. Evitar el uso de soya mal procesada con contenido alto de inhibidores de tripsina. Maintaining Gut Integrity By Dr. Harish V. Dharne, head of Avitech’s Business Promotion and Knowledge Resource Centre Nutrition and gut health are closely related in commercial poultry production. Diet formulation and feed management can have a marked effect on gut health greatly influencing nutrient utilization and growth of the animal. Gut health problems arise due to improper nutrition and an unhygienic environment especially during the early stages of chick development. For cost effective and sustainable commercial operations there is need to: 1. Maintain natural gut health through proper nutrition and a clean environment, and 2. Effective treatment of an existing gut disorder. TGI: FUNCION Y ESTRUCTURA To improve gut health, a clear understanding of the STRUCTURE AND FUNCTIONALITY OF THE GUT is important.. Birds also have high numbers of intestinal villi and high EPITHELIAL TURNOVER RATE (48 TO 96 H), and rapid inflammatory response (less than 12 hours, as compared to 3-4 days in mammals), which makes them more susceptible to disturbances in absorptive capacity than mammals. Transit time and pH in poultry GIT GIT Segment Transit Time(Min) pH Crop 50 5.5 Proventriculus / gizzard 90 2.5-3.5 Duodenum 5-8 5-6 Jejunum 20-30 6.5-7.0 Ileum 50-70 7.0-7.5 Colon 25 8.0 Source: R.Gauthier(2002) Natural Physical Barriers that Help to Maintain Intestinal Integrity Physical barriers protect against the entry of foreign materials and organisms into the bloodstream and access to other viscera thus helping intestinal integrity. On occasion due to improper nutrition or an unhygienic environment, when the load of foreign invaders increase these barriers are breached. 1. Mucus (a protective1. Mucus: material secreted by intestinal cells) is a barrier to bacterial and fungal invasion. It is broken by some enzymes (eg. mucinolytic, urease). Poultry feeds with under cooked soy meal may contain urease. 2. Gut epithelial cells (enterocytes): These cells form a semi-permeable surface that selectively allows passage of fluid, electrolytes, and dissolved nutrients. Every epithelial cell in the digestive tract is part of a continuous physical barrier. When organisms and toxic agents damage epithelial cells, the integrity of this protective barrier is broken. 3. Fluid secretion: fluid having large amounts of water mixed with electrolytes. The fluid in the upper small intestine is protective and keeps bacteria in suspension and washes them downstream. 4. Vascular supply: supply under the gut epithelial layer serves to rapidly dilute and carry away any agents or chemicals (endogenous or exogenous) that may breach the mucosal barrier. Factors Influencing Gut Integrity a. Physical barriers: Intestinal integrity is compromised when the mucus layer is degraded; epithelial cells are effaced or destroyed, the vascular supply is interrupted, or the immune system is compromised. Viruses, bacteria, fungi, parasites, and toxins can damage this. b. Stress factors: Gut environment is also altered by several stress factors to the birds like handling, transportation, overcrowding, abrupt changes in environment etc. c. Feed toxins and toxicants: Feed toxins and toxicants can also affect the gut integrity. d. Dietary factors: Nutritional deficiency due to imbalance in ration formulation, grain engorgement, microbial load in feed etc. affect gut health. The nature of the diet, for example presence of non-starch polysaccharide (NSP) especially soluble fractions in the diet provide substrate for the growth of undesirable bacteria and accumulation of fermentation products affecting the gut severely. Insoluble NSP is a major problem leading to soiling of litter. e. Health status: Diseases like coccidiosis and fowl plague are found to affect the gut integrity severely. Infections, injuries etc. also affect gut health. f. Gut micro flora: The rich bacterial community that make up the gut micro flora play an important role for the host through changes in the morphology of gut, nutrition, pathogenesis of enteric diseases, immune response and alterations in colonization resistance. The shift in composition of this microflora results in production and efficiency losses often in the absence of any clinical signs. Useful microbes (commensal bacteria) in gut play a positive role in controlling the gut flora and stimulate the development of the gut wall. Hence, microbial balance of gut is utmost important in maintaining gut integrity. g. Beak deformity: Beak deformity preventing proper feed consumption may impair gut health. Early Chick Nutrition and Gut Health Good start is an important factor in MAXIMIZING PROFITS from broiler operations. Early nutrition mainly in the first 7 days of life for broilers may program the birds' systems and set a pattern for growth and productivity. A large percentage of early growth (2 to 5 times the growth rate of other tissues) occurs in the digestive tract and those organs involved in digestion. If digestive growth is retarded during this time period, overall growth rate may be compromised. Further newly hatched chicks are more prone to gut infections as its natural defense is yet to be strengthened. So proper care should be taken during this time period. Feeding of chicks: Access to nutrients post hatch has a major impact on the immediate and long-term development of the chick. The immediate post hatch period is critical for the development of all systems in chicks including the immune system. The development of bursa and spleen is responsive to environmental stress at an early age in chicks. Delayed access to nutrients post hatch reduces the relative weight of bursa and spleen. The passage of feed that is not sterile, through TGI exposes the bursa to a variety of antigens. So the earlier the chicks are fed post hatch, the sooner will the proliferation stem cell meet environmental antigens. This clearly suggests that early nutrition is important in laying a strong foundation for the health status of birds in a situation where little or no antibiotics are allowed in their feed. Suitable feed additives should be added in the starter diet as precautionary measure that will ensure better health and productivity. Role of Dietary Factors in Improving Intestinal Integrity Quality feed ingredients: Supplementation of quality feed ingredients helps in maintaining natural gut health. Processed feed: Many incriminating factors of feed are destroyed due to processing. Extrusion is effective in reducing microbial contamination in feedstuffs and in Salmonella control. Pelleted feed: Pelleting provides scope for utilization of high fibre feed resources. Use of steam- pelleted feed seems to be of value in maintaining gut health. Feed additives: Commercial poultry production during the last 50 years has benefited from pharmaceutical and biological products that enabled flock size to increase, genetic potential and improved nutritional formulations to be realized, and overall production to increase. Food animal agriculture is providing wholesome poultry meat protein for consumption in the human diet at unprecedented levels. Some feed additives that promote the gut health either directly or by preventing the enteric pathogens are discussed below ADITIVOS QUE PROMUEVEN SALUD DEL TGI ANTICOCCIDIALS AND IONOPHORES; coccidiosis, a managemental disease, causes devastating losses to the poultry industry. The disease is characterised by an invasion and damage of the intestinal wall by the parasite resulting in severe haemorrhage and mortality. For this reason, it is essentially added in most poultry rearing situations during the rearing period to prevent illness and control infections. When used in a structured and monitored programme, anticoccidial agents are very effective and permit the optimum performance of the animal without compromising health status. No new anticoccidial agent has come onto the market since the 1980s, which is in part a reflection of the success that the ionophores have brought to the control of the disease. PROBIOTICS (DIRECT-FED MICROBIALS); “A probiotic is defined as a live microbial feed supplement which beneficially affects the host animal by improving its INTESTINAL MICROBIAL BALANCE.” Gut flora may be disturbed under several circumstances including the use of antibiotics or other drugs, excess stress, disease, exposure to toxic substances, which allows harmful competitors to thrive in the gut. Probiotics prevent such harmful bacteria (enteric pathogens) from growing in the gut and thus minimize the disturbances caused by them, and also maintain host favourable bacteria. Thus Probiotics balance gut microflora. Probiotics are also used as an alternative to antibiotics. However, probiotics are not a substitute for antibiotics in birds with serious infections but are useful in restoring the normal bacterial population that was otherwise altered due to administration of antibiotics. If the conditions that originally caused damage to the natural gut flora persist, the benefits obtained from probiotic supplements will be short lived. PREBIOTICS; are non-digestible food ingredients (readily fermentable sugars), that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and thus improve host health. Most potential prebiotics are carbohydrates (such as oligosaccharides). Prebiotic oligosaccharides may be added to processed foods. Some prebiotics that are used in this manner against pathogens are fructo-oligo-saccharides (FOS), xylo-oligo-saccharides (XOS), mannan-oligo-saccharides (MOS) and galacto-oligo- saccharides (GOS). SYNBIOTICS; although use of probiotic formulations may well help in achieving these benefits, it is also possible to increase and maintain a healthy bacterial gut flora by increasing the amounts of prebiotics in the diet such as inulin (naturally occurring oligosaccharides), raw oats, and unrefined wheat. As probiotics are mainly active in the small intestine and prebiotics are only effective in the large intestine, the combination of the two gives a synergistic effect. Appropriate combinations of pre- and probiotics are termed as synbiotics. ACIDIFIERS/ORGANIC ACIDS; include short chain fatty acids, volatile fatty acids and weak carboxylic acids that are only partly disassociated. They may play a role in maintaining gut integrity in the way that they reduce the colonization of pathogens (like Salmonella and E.coli) in intestinal wall by lowering the intestinal pH below 6.0, and promoting the normal microflora growth. This condition also increases the efficiency of all digestive enzymes. Daily application of short chain fatty acids such as Butyric acids increases epithelial cell proliferation, quick repairing of the intestine, increased villous height and in turn increased absorptive capacity. Alone or in combination, these are beneficial to the animal's health. ENZYMES; extra enzymes can add to the animals' own digestive capacity. Feeding high viscosity cereal grains to broilers result in larger microbial populations in the ileum. Viscosity reduces the passage rate of the feed leading to overall reductions in consumption and decreased performance, sticky droppings and dirty eggs. A viscous environment slows down digestion processes, and encapsulates nutrients, making them inaccessible to digestive enzymes. Viscous gels are formed in the digesta by the soluble NSP, which are not digested by the animal's own enzymes. Thickening of unstirred water layer due to gel formation also inhibit absorption. Thus non-starch polysaccharides form a major target substrate for feed enzymes. The addition of enzymes to address NSP viscosity can improve gut health, feed efficiency, improve manure quality and facilitate the use of lower cost feed ingredients. TOXIN BINDERS; are used through feed to bind or adsorb deleterious substances such as mold and fungi-borne mycotoxins. These are the invisible thieves or a hidden danger in animal feed, to animal health and production. They may also accumulate in animal products and contaminate the human food chain. ANTIBIOTIC GROWTH PROMOTERS; With the intensification of livestock farming the use of antibiotics for growth promotion has become popular. Antibiotic growth promoters are feed additives that are administered at a low, sub therapeutic dose to suppress sensitive populations of bacteria in the gut and improve growth and performance of bird. The reason is that a reduction in gastrointestinal infections would result in the subsequent increase in muscle weight. It has been estimated that as much as 6 per cent of the net energy in the diet could be lost due to microbial fermentation in the intestine (Jensen, 1998) and stimulation of energy-consuming immune responses. If the microbial population could be better controlled, it is possible that the lost energy could be diverted to growth. Whatever the mechanism of action, the result of the use of growth promoters is an improvement in daily growth rates between 1 and 10 per cent resulting in meat of a better quality, with less fat and increased protein content Limitaciones del uso de los antibioticos: An overuse of any antibiotic over a period of time may lead to the local bacterial populations becoming RESISTANT TO THE ANTIBIOTIC. ANTIBIOTIC RESIDUES in the products may affect humans. Essentially, there are two main ways in which we can reduce our dependence on antibiotic use in animals: 1. An obvious choice is the development of ALTERNATIVES TO ANTIBIOTICS that work via similar mechanisms, promoting growth whilst enhancing the efficiency of feed conversion. 2. A more difficult route would be to IMPROVE ANIMAL HEALTH.