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Algunos factores siolgicos y nutricionales queafectan la incidencia de diarreas posdestete en

lechones

Some physiological and nutritional factorsaffecting the incidence of post-weaning diarrhea

in piglets

Recibido el 3 de diciembre de 2009 y aceptado el 12 de agosto de 2010.Facultad de Ciencias Naturales, Universidad Autnoma de Quertaro, Av. de las Ciencias s/n. Juriquilla, 76000, Quertaro, Quertaro,Mxico.**CENID Fisiologa INIFAP, km 1 Carretera a Coln, 76280, Ajuchitln, Coln, Quertaro.Correspondencia: Trcia Cesria Reis de Souza, Tel.: (442) 1 92 12 00, extensin 5391, Fax: (442) 2342958, Correo electrnico: tercia@uaq.mx

Abstract

Weaning causes disturbances in the digestive unction and intestinal health o piglets and is almost always associated with a

severe growth depression and diarrhea. For this reason antibiotics in sub-therapeutic doses are oten added to eed to prevent

diarrhea and as growth promoters. However, due to the ban o antibiotics in eedstus in dierent parts o the world, an increase

in post-weaning diarrhea in piglets has been observed. Several nutritional strategies have been used as control measures. This

work reviews some aspects o nutrition, digestive physiology, intestinal microora in weaned piglets and their relationship with

post-weaning diarrhea. It is concluded that the use o probiotics and prebiotics in pig starter diets may be an alternative to

replace antibiotics in post-weaning diarrhea control. Fed piglets ater weaning with a low crude protein die t (17%) instead to high

crude protein diets (23% or more) , may also be an efcient strategy to diarrhea control through the reduction in the urea nitrogen

level in plasma and the production o microbial toxic metabolites such as ammonia, which indicates a reduction in the ermenta-

tion o proteins and contributes to maintain intestinal health.

Key words:PIGLETS, WEANING, CRUDE PROTEIN LEVEL, DIARRHEA.

ResumenEl destete produce perturbaciones en el uncionamiento digestivo y en la salud intestinal de los lechones y casi siempre se asocia

con una severa depresin del crecimiento y diarrea. Por ello, con recuencia se agregan dosis subteraputicas de antibiticos al

alimento como medida preventiva contra las diarreas y como promotores de crecimiento. Sin embargo, debido a la prohibicin

del uso de antibiticos en la alimentacin animal, en dierentes partes del mundo se ha observado un incremento de las diarreas

posdestete en lechones. Para contrarrestar este problema se ha promovido el uso de estrategias nutricionales como medidas de

control. El presente trabajo tuvo como objetivo revisar algunos aspectos relacionados con la nutricin, la fsiologa digestiva, la

microbiota intestinal de lechones re cin destetados y su relacin con las diarreas posdestete. Se concluy que el uso de probiti-

cos y prebiticos en las raciones iniciadoras puede ser una alternativa para reemplazar los antibiticos en control de las diarreas

posdestete. Alimentar a los lechones despus del destete con dietas con niveles bajos de protena cruda (17% de PC, en lugar de

23% o ms) tambin puede ser una estrategia efciente para controlar diarreas. Esto a travs de la reduccin del nivel de nitrgeno

ureico plasmtico y de la produccin de metabolitos microbianos txicos, como el amoniaco, lo que indica una reduccin en la

ermentacin de protenas y contribuye a mantener la salud intestinal.

Palabras clave: LECHONES, DESTETE, NIVEL DE PROTENA CRUDA, DIARREA.

Trcia Cesria Reis de Souza* Gerardo Mariscal Landn** Konisgmar Escobar Garca*

Artculo de revisin

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Introduction

Weaning o piglets alters digestive unctioningand intestinal health. Maternal milk ingestionsuppression is not immediately compensatedby appropriate water consumption or by enough salivaand gastrointestinal secretion production. Underthese conditions, the inherent stress o this stage may

cause increased peristaltic movements and even anabrupt interruption o the synthesis o certain enzymes,giving origin to diarrheas on the same day they areweaned.1 These problems become more serious inearly-weaned piglets, when they are compared to thoseweaned at our and six weeks o age.2 Nevertheless, inorganic pigs production, where weaning is later (sevenweeks in Denmark), post-weaning diarrheas are also aproblem.3

A piglet that has been recently weaned demandsa high amount o energy or physiological processesrelated to body development and maturation o theimmunological system.4 Paradoxically, the necessary

digestive capacity or piglets to use nutrients best isquite limited during the post-weaning period, sincethe organs o the gastrointestinal tract are not welldeveloped and the activity o the digestive secretionsis low.5 The problem is graver with vegetable originproteins, since they are less susceptible to enzymaticdigestion than those o animal origin.6 Thus during thepost-weaning period, when the piglet starts consumingsolid diets based on vegetable raw materials, there is anincreased susceptibility to gastrointestinal disorders.1The above contributes to making this period themost critical one during the liespan o the pig, sincethere is a phase o anorexia and undernourishment7that aects digestive physiology and development othe animals. During the last decades there have beengreat advances in the ormulation o rations or therst rearing phase, in order to adapt piglets to a post-weaning diet based on vegetable origin carbohydratesand proteins, thus reducing the risk o post-weaningdiarrheas. These diets normally include antibiotics atdoses below therapeutic levels8 as a diarrhea preventionmeasure and growth promoters.9 Nevertheless, recentlydue to the ban o antibiotics in animal eed in dierentparts o the world, post-weaning diarrheas (PWD) haveincreased in piglets.10 In order to block this problem,

the use o nutritional strategies has been promotedto control PWD,8,9,11-14 including the manipulation othe diet ingredients in order to modiy pathogenicand commensal bacterial populations.2 Among theproposed nutritional solutions, the reduction o crudeprotein levels (CP) in the diet has been one o themost studied alternatives 2,3,10,13,15-19 to reduce digestiveproblems in piglets. The objective o this study was toreview certain aspects related to the nutrition o newly

Introduccin

El uncionamiento digestivo y la salud intestinalde los lechones son perturbados por eldestete. La supresin de la leche materna noes inmediatamente compensada por un consumoadecuado de agua o por una suciente secrecinsalival o gastrointestinal. En este contexto, el estrs

inherente a esta etapa puede ocasionar un aumentodel peristaltismo y hasta una interrupcin abrupta dela sntesis de algunas enzimas; originando diarreas enel mismo da del destete.1 Esta problemtica resultser ms importante en lechones destetados a unaedad temprana, cuando se compararon a cuatro yseis semanas de edad;2 sin embargo, en la produccinde cerdos orgnicos, en la cual el destete se realizams tardamente (siete semanas en Dinamarca), lasdiarreas posdestete tambin son un problema.3

El lechn recin destetado es un animal altamentedemandante de energa para los procesos siolgicosrelacionados con el desarrollo corporal y la maduracin

de su sistema inmunolgico.4 Paradjicamente, lacapacidad digestiva necesaria para que los lechonesaprovechen los nutrimentos es bastante limitada enel periodo posdestete, pues los rganos del tractogastrointestinal estn poco desarrollados y la actividadde las secreciones digestivas es baja;5 el problema esms grave con las protenas de origen vegetal, puesson menos susceptibles a la digestin enzimtica quelas de origen animal.6 As, en el periodo posdestete,cuando el lechn empieza a consumir dietas slidascon base en materias primas vegetales, se incrementasu susceptibilidad a los desrdenes gastrointestinales.1Lo anterior contribuye a que este periodo sea el mscrtico en la vida del cerdo, pues se presenta unaase de anorexia y subnutricin7 que repercute en lasiologa digestiva y en el desarrollo de los animales.En las ltimas dcadas se ha observado un gran avanceen la ormulacin de las raciones de la primera asede la crianza, para adaptar a los lechones a una dietaposdestete a base de carbohidratos y de protenas deorigen vegetal, reduciendo as el riesgo de las diarreasposdestete. Estas dietas normalmente incluyen dosissubteraputicas de antibiticos8 como una medidapreventiva contra las diarreas y como promotoresde crecimiento.9 Sin embargo, recientemente,

debido a la prohibicin del uso de antibiticos en laalimentacin animal en dierentes partes del mundo,han incrementado las diarreas posdestete (DPD) enlechones.10 Para contrarrestar este problema se hapromovido el uso de estrategias nutricionales comomedidas de control de las DPD,8,9,11-14 incluyendo lamanipulacin de los ingredientes de la dieta paramodicar las poblaciones bacterianas patgenasy comensales.2 Entre las soluciones nutricionales

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weaned piglets and the consequences on digestivephysiology and intestinal microbiota; and to analyzethe ecacy o certain nutritional strategies in thereduction o incidence and severity o post-weaningdiarrheas.

Weaning and digestive physiology

At the time o piglet weaning, the change rom milkeeding to a solid diet is requently associated with asevere growth depression and the presence o diarrheagiving way to the so-called post-weaning diarrheasyndrome with a multiple actor etiology (handling,diet composition, hygiene, among others); anorexiaand undernourishment are important actors thattrigger this syndrome.3,14,20-24 Figure 1 illustrates howthese actors interact turning into diarrheal processes.During the rst 24 to 36 hours ater weaning, changesin the small intestinal mucosa are observed at theunctional and structural levels, mainly villi atrophyand hypertrophy o Lieberkhn crypts with a reduction

between 20% to 30% o this organs weight.23,24 Also,certain anti-nutritional actors ound in vegetableorigin proteins may cause hypersensitivity reactionsat the intestinal epithelium level, compromisingintestinal health even more as well as its enzymaticactivity. Taking also into consideration morphologicalalterations o the intestinal villi, with the loss omature enterocytes rich in digestive enzymes, thatare observed during the post-weaning period, thereis a reduction o brush border enzyme activity.22,25Interaction between pancreatic enzymes, trypsin andchymotrypsin, with anti-trypsin actors reduces theiractivities, since they compete or the enzyme-substratepoint o union, aecting protein digestibility o thediet.26 Through molecular studies it was observed thatimmediately ater weaning the levels o messengerRNA (mRNA) in the pancreas are low and thereorethere is a reduction in pancreatic enzyme synthesisduring this period.24 Nevertheless, a ew days later,pancreatic levels o mRNA and enzymatic activity wererestored, with the exception o lipase activity. Duringthis period, digestive enzymes have low synthesis,secretion and activity, and the digestive process ishighly compromised and the non-digested and non-absorbed nutrients that are present in the intestinal

lumen serve as substrate or enteropathogenic bacteriasuch as E. coli, with their subsequent prolieration,causing diarrheas (colibacillosis) that may increasemorbidity and mortality during post weaning stage.27Intestinal health may be maintained and colibacillosiseects minimized i weaning age is increased and dietprotein level is reduced;2 this is especially importantin early-weaning, especially under environments thatare adverse to piglet health. Table 1 summarizes the

propuestas, la reduccin del nivel de protena cruda(PC) dietaria ha sido una de las alternativas msestudiadas2,3,10,13,15-19 para disminuir los problemasdigestivos en los lechones. El presente trabajo tuvocomo objetivo revisar algunos aspectos relacionadoscon la nutricin de los lechones recin destetados,y sus consecuencias en la siologa digestiva y enla microbiota intestinal; y analizar la ecacia de

algunas estrategias nutricionales en la reduccin de laincidencia y severidad de las diarreas posdestete.

El destete y la siologa digestiva

Al momento del destete de los lechones, el cambiode la alimentacin lctea por una racin slida estrecuentemente asociado con una severa depresin delcrecimiento y con la presencia de diarrea, dando lugaral denominado sndrome de las diarreas posdestete,con una etiologa multiactorial (manejo, composicinde las dietas, higiene, entre otros); la anorexia y lasubnutricin son los actores desencadenantes ms

importantes de este sndrome.3,14,20-24 La Figura 1ilustra cmo interactan los actores que conducen alos procesos diarreicos. Durante las primeras 24 a 36horas posdestete se observan cambios en la mucosadel intestino delgado a nivel uncional y estructural,principalmente con atroa de las vellosidades ehipertroa de las criptas Lieberkhn, con unareduccin de entre 20 y 30% del peso de este rgano.23,24Aunado a ello, algunos actores antinutrimentalespresentes en las protenas dietarias de origen vegetalpueden causar reacciones de hipersensibilidad a niveldel epitelio intestinal, agravando an ms la saludintestinal y su actividad enzimtica. Considerandotambin que las alteraciones morolgicas delas vellosidades intestinales, con las prdidas deenterocitos maduros ricos en enzimas digestivas,observadas en el periodo posdestete, traen comoconsecuencia una disminucin en la actividad de lasenzimas del borde de cepillo.22,25 La interaccin de lasenzimas pancreticas, tripsina y quimotripsina, con losactores antitrpsicos, disminuye sus actividades, puesstos compiten por el punto de unin enzima-sustrato,aectando la digestin de las protenas provenientes dela dieta.26 A travs de estudios moleculares se observque inmediatamente despus del destete, los niveles

de ARN mensajero (ARNm) en el pncreas son bajos,por lo que hay una disminucin en la sntesis de lasenzimas pancreticas en este periodo.24 Sin embargo,pocos das despus, los niveles pancreticos de ARNmy la actividad enzimtica ueron restaurados, conexcepcin de la actividad de la lipasa. Durante esteperiodo de baja sntesis, secrecin y actividad de lasenzimas digestivas, el proceso digestivo est altamentecomprometido y los nutrimentos no digeridos y

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Figura 1. Procesos que desencadenan el sndrome de las diarreas posdestete.22 Las fechas indican una disminucin y las un incremento delactor considerado.TGI = tracto gastrointestinal.

Figure 1. Processes that trigger post-weaning diarrheal syndrome.22 Downward arrows indicate a reduction and upward arrows an increase othe actor taken into consideration.GIT = gastrointestinal tract.

Diet changes

Fasting

Enviromental change

Stress

Infections

Multiple factor etiology

GIT Development

+

Function alterations

Defenses

Digestion Absorption

Substrate

Microflora

Growth/adhesion of pathogenic bacteria

(E.coli, for example)

Resistance to pathogenic

bacteria colonization

Toxins production

DIARRHEA

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above, presenting the context within which weaningis carried out, the induced enteric disorders and themain risk actors or the presentation o post-weaningdiarrheas.24

Digestive use of nutriments and diarrheas

It is known that digestibility o a nutriment is

a consequence o the digestive process and an

no absorbidos, presentes en la luz intestinal, sirvende sustrato para las bacterias enteropatgenas (E.coli, por ejemplo), haciendo que stas prolieren ycausen enermedades diarreicas (colibacilosis) quepueden aumentar la morbilidad y la mortalidad en laetapa posdestete.27 Aumentando la edad al destete ydisminuyendo el nivel de protena dietaria se puedecontribuir a mantener la salud intestinal y minimizar

los eectos de la colibacilosis posdestete.2 Disminuir elCuadro 1

CONTEXTO EN QUE SE REALIZAN LOS DESTETES, DESRDENES INTESTINALES

INDUCIDOS Y PRINCIPALES FACTORES DE RIESGO24

CONTEXT WHEREIN WEANINGS TAKE PLACE, INDUCED INTESTINAL DISORDERS AND

MAIN RISK FACTORS24

Context: weaning is directly related to animal immaturity added to multiple factor origin stress.

Immaturityoftheanimalintermsof:

o Behavior (in general and feeding).

o Gastrointestinal tract functioning (secretion, motility, absorption, defense, etcetera).

o Immune system (intestinal and general).

Psychologicalstress

o Abrupt separation from the mother.

o Mixture with piglets of other litters.

o New environment (nursery, production unit, farm, etcetera).

Nutri tionalstress

o Milk suspension: highly palatable and digestible liquid, etcetera).

o Dry feed access (solid, less palatable, less digestible).

o Access to drinking water separate from feed.

Induced intestinal disorders

Alterationsinintestinalarchitectureandfunction:

o Morphology: villi atrophy followed by crypt hypertrophy.

o Reduction of intestinal digestive enzymes activity.

o Intestinal absorption, secretion and membrane permeability alterations

Associatedentericpathogens:

o Bacteria (enteric toxigenic or pathogenicEscherichiacoli).

o Virus: rotavirus.

Principal risk factors

Nutritionalfactors:

o Low or erratic feed consumption.

o

Presence of anti-nutritional factors (anti-trypsin factor, lectins, antigens, etcetera).o Diets with complex components that have low digestibility (vegetable proteins and carbohydrates).

o High protein levels (high buffering capacity).

Handling

o Numerous litter/ low weaning weight.

o High piglet density in weaning installations.

o Low hygienic level.

o Not appropriate environment (low temperature, low quality air, etcetera).

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indirect estimate o their absorption and thereoreit is a measure o nutritional value o eed. From theevaluation o digestibility o the dierent nutrimentsin the starter diet, it is possible to measure the digestivecapacity o the animal and the degree o tolerance it hasto eed.28 Digestibility is mathematically expressed asthe dierence between the ingested and the excretedamounts o a nutriment, divided by the ingested

amount.29 In a review o the literature30 dierent ormso nutriment digestibility expression are discussed.Ileal level measurements are more appropriate toexpress the availability o dietary protein and at inthe digestive apparatus o the newly weaned piglet,31since the microorganisms o the large intestine usenutrients that have not been absorbed in their passingthrough the intestine up to the ileum, increasing ecaldigestibility values signicantly.32-34 Nevertheless, theexpression o ecal digestibility is more appropriateto estimate the use o eed dry matter and thereoreits energy,35 due to the importance o bacterialermentation o non-amylaceous polysaccharides o

eed, that generate short chain volatile atty acids thatare strong source o energy or animals.36

There is a negative relationship between theapparent ecal digestibility o energy and thepresence o diarrhea.37 For example, pea starch haslower digestibility than the one rom cereals and itsincomplete digestion in the small intestine can increasethe ermentation process in the large intestine, whichcorresponds to an increase in ecal digestibility oenergy.38 In consequence excessive ermentationin the caecum and colon causes diarrheas anddehydration.38 It is known that protein componentso vegetable origin have lower ileal digestibility thanthose o animal origen.39 Diet protein that exceedsdigestion and absorption capabilities, together withthe one o endogenous origin that was not digestedand not reabsorbed in the small intestine, continueinto the large intestine where microbial fora ermentsit, producing toxic products such as ramied chainvolatile acids, biogenic amines, phenolic compounds,ammonia and sulhydric acid that can harm animalhealth and cause diarrheas as well as detrimental eectson their development.13,40 In several bibliographicalreviews 11,41-44 the eect o proteinic ermentation andsynthesis o toxic compounds in the large intestine are

analyzed.Both weeks that ollow weaning represent the mostdicult period or the digestive use o nutriments andit is when the piglets are more sensitive to dierentactors that negatively aect digestibility in the anteriordigestive tract.45 Perhaps that is the reason why atthis age they are more susceptible to gastrointestinaldisorders.18

contenido de protena dietaria suele ser especialmenteimportante en los destetes precoces, particularmenteen ambientes adversos a la salud de los lechones. Enel Cuadro 1 se resumen los puntos anteriormentemencionados, presentando el contexto en quese desarrolla el destete, los desrdenes entricosinducidos y los principales actores de riesgo para laaparicin de las diarreas posdestete.24

Utilizacin digestiva de los nutrimentosy diarreas

Se sabe que la digestibilidad de un nutrimentoes una consecuencia del proceso digestivo y unaestimacin indirecta de su absorcin es, por tanto,una medicin del valor nutritivo de los alimentos.A partir de la evaluacin de la digestibilidad de losdierentes nutrimentos de la racin de destete, esposible medir la capacidad digestiva del animal y sugrado de tolerancia a los alimentos.28 La digestibilidadse expresa matemticamente como la dierencia de la

cantidad ingerida y la excretada de un nutrimento,entre la cantidad ingerida.29 En una revisinbibliogrca30 se discuten las dierentes ormas deexpresin de la digestibilidad de los nutrimentos.Las mediciones a nivel ileal son ms apropiadas paraexpresar la disponibilidad de la protena y de la grasadietaria en el aparato digestivo de los lechones recindestetados,31 debido a que los microorganismosdel intestino grueso utilizan los nutrimentos noabsorbidos hasta el leon, aumentando los valores dedigestibilidad ecal de manera signicativa.32-34 Sinembargo, la expresin de la digestibilidad ecal es lams apropiada para estimar la utilizacin de la materiaseca del alimento y, consecuentemente, de su energa,35dada la importancia de la ermentacin bacteriana delos polisacridos no amilceos de los alimentos, la cualgenera cidos grasos voltiles de cadena corta, que sonuente de energa para los animales.36

Existe una relacin negativa entre la digestibilidadecal aparente de la energa y la presencia de diarreas.37Por ejemplo, el almidn de chcharos tiene una menordigestibilidad ileal que el proveniente de los cereales, ysu incompleta digestin en el intestino delgado puedellevar a un incremento del proceso ermentativo en elintestino grueso, lo que corresponde a un aumento

en la digestibilidad ecal de la energa.38

Comoconsecuencia de la excesiva ermentacin en el ciegoy colon se provocan diarreas y deshidratacin.38 Sesabe que los componentes protenicos del alimentode origen vegetal tienen menor digestibilidad ilealque los de origen animal.39 La protena dietariaque excede la capacidad de digestin y absorcin,adems de la de origen endgeno no digerida y noreabsorbida en el intestino delgado, pasan al intestino

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Digestive tract health and intestinalmicrobiota

Intestinal health may be dened as the capacity othe gastrointestinal tract (GIT) to maintain itsel inbalance, since it is a constantly changing ecosystem. 46Diet, mucosa, and commensal microbiota are threemain components o intestinal health. Certain

components o the diet or weaned piglets, such assoy paste may harm intestinal mucosa, cause intestinalliquid accumulation and predispose the piglet to post-weaning diarrhea.11 Development o the immunesystem o the intestinal mucosa depends on commensaland pathogenic bacteria colonization.7 Mucosa isormed by digestive epithelium, lymphoid tissueassociated with the intestine (LTAI) and mucus thatcovers the epithelium. LTAI, commensal microbiotaand mucus interact with host cells; generate a sensitiveand dynamic balance in the GIT, insuring correctunctioning o the digestive process.47

In animal nutrition, the challenge created by theban o antimicrobial growth promoters has called ora search o instruments capable o rendering betterknowledge o intestinal microbiota components, inother words, the set o microorganisms that ormone o the most interesting symbiotic microcosms othe animal kingdom.48 GIT microbiota is a complexecosystem that contains several thousands o bacterialspecies that have an important role in intestinal health,preventing colonization by potentially pathogenicmicroorganisms.49 Traditionally, studies that analyzedthe eects o raw materials or additives would useclassic microbiology to count certain microorganisms,

that in general were easily cultured, allowing a partialvision o the changes that might happen in thedigestive tube lumen.48 Nevertheless, only between0.1% and 10% o the bacteria in this environment canbe grown in the laboratory,50 since many o the strictlyanaerobic microorganisms are undetectable withconventional microbiological culture techniques.40,51,52These limitations in culture techniques are overcomewith the development o the molecular tools, whichallow the detection and identication o bacteria basedon ARNr 16S gene diversity sequencing. Thanks tothese techniques, knowledge about the developmentand modications to microbial fora composition

in the intestine has greatly advanced during the lastew years. Recently, phylogeny analysis o ARNr 16Sgene subunit rom swine GIT, revealed a very complexmicrobial population whose most bacterial specieshave not been characterized yet.53 Authors o thisstudy gathered a library o 4,270 clone sequences othe ARNr 16S gene, representing 375 phylotypes romthe ileum, caecum, and colon o pigs between 12 and18 weeks o age. These thousands o bacterial species

grueso y la fora microbiana las ermenta, produciendoproductos txicos, como cidos voltiles de cadenaramicada, aminas biognicas, compuestos enlicos,amoniaco y cido sulhdrico que pueden ser dainosa la salud de los animales, causando diarreas y eectosdetrimentales en su desarrollo.13,40 En dierentesrevisiones bibliogrcas11,41-44 se discuten los eectos dela ermentacin protenica en el intestino grueso y la

sntesis de compuestos txicos.Las dos semanas que siguen al destete representanel perodo ms dicil para la utilizacin digestiva de losnutrimentos, y es cuando los lechones son ms sensiblesa los dierentes actores que aectan negativamente ladigestibilidad en el tracto digestivo anterior.45 Tal vezpor eso a esta edad son ms susceptibles a los trastornosgastrointestinales.18

La salud del tracto digestivo y lamicrobiota intestinal

La salud intestinal puede ser denida como la

capacidad del tracto gastrointestinal (TGI) demantenerse en equilibrio, ya que es un ecosistemaen constante cambio.46 Existen tres principalescomponentes de la salud intestinal: la dieta, la mucosay la microbiota comensal. Ciertos componentes dela dieta para lechones destetados, como la pasta desoya, pueden causar daos de la mucosa intestinal,acumulacin de lquido intestinal y predisponer adiarreas posdestete.11 El desarrollo del sistema inmunede la mucosa intestinal depende de la colonizacinpor bacterias comensales y patgenas.7 La mucosa estcompuesta por el epitelio digestivo, el tejido linoideasociado con el intestino (TLAI) y el moco que recubreel epitelio. El TLAI, la microbiota comensal y el mocointeractan con las clulas del hospedero, generanunsensible y dinmico equilibrio en el TGI, asegurandoel correcto uncionamiento del proceso digestivo.47

En el rea de nutricin animal, el reto planteadopor la prohibicin de los antimicrobianos promotoresde crecimiento, ha hecho que se busquen instrumentoscapaces de aportar un mayor conocimiento de loscomponentes de la microbiota intestinal, es decir,del conjunto de microorganismos que conormanuno de los microcosmos simbiticos ms interesantesdel reino animal.48 La microbiota del TGI es un

ecosistema complejo que contiene varios miles deespecies de bacterias, las cuales tienen un papelimportante en la salud intestinal, previniendo lacolonizacin de microorganismos potencialmentepatgenos.49 Tradicionalmente, los estudios queanalizaban los eectos de las materias primas oaditivos sobre la microbiota intestinal recurran a lamicrobiologa clsica para hacer recuentos de algunosmicroorganismos, en general cilmente cultivables,

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in the GIT, orm a very complex ecosystem, have animportant role in global wellbeing o the animal,54 andabove all in intestinal health, preventing colonizationby potentially pathogenic microorganisms.49

When they are born, piglets become exposed inthe nursery to environmental microorganisms andmaternal microbial fora and her eces all o whichintroduce bacteria that colonize the digestive tract.54

These bacteria look or the most appropriate niche orthem and compete and interact among themselves,constituting nally a relatively stable and complexpopulation that represents the normal intestinalmicrobiota.54 In the lactating piglet, dominantbacteria in the stomach and small intestine are usuallylactobacilli and streptococci, both groups well adaptedto the use o the available milk substrate.54 Microbiotathat develops in the large intestine shortly ater birthis constituted by an extensive and varied selection obacteria that are mostly strict anaerobes, includingbacteroides, bidobacteria, eubacteria, streptococciand lactobacilli; likewise, other microorganisms can

be ound in lower density such as enterobacteria.Normally, bacteroides is the most numerous genusand it may come up to 30% o the total. 55 Normalmicrobial fora that is established ater birth interactswith the digestive and immunological systems o thebody and their activities may be benecial or harmulto the animal.7 Colonization o the dierent intestinalcompartments by specic commensal bacteria,especially through the association with mucus oradhesion to the epithelial cells, serves as a rst deensebarrier against invading organisms or toxic substancespresent in the diet. At the time o weaning, during ashort period, changes in intestinal microbiota occurin terms o amount and quality, which evolves into acomplex and stable community.52 Intestinal microbiotadevelopment is a gradual and sequenced process thatdepends on nutritional and non-nutritional actors.52,56It has been reported57 that intestinal microbiotacomposition in piglets diers between individuals,even though the animals may be consuming the samediet.

Incidence and severity of post-weaningdiarrheas

In experimental studies, incidence and severity odiarrheas are determined by visual appreciation oeces consistency. Most o the times a scale is used,where grades are given rom 0 to 3.37Value 0 indicatesnormal eces and thereore no diarrhea presence; thevalue o 1 describes a slight pasty diarrhea; value 2, amoderate semi-liquid diarrhea; value 3 a severe veryliquid diarrhea. Daily grades during the experimentalperiod are summed and an index o severity o the

que permiten una visin parcial de los cambios quepudieron ocurrir en el interior del tubo digestivo.48Sin embargo, slo entre 0.1% y 10% de las bacteriasen el ambiente es cultivable,50 ya que muchos de losmicroorganismos estrictamente anaerbicos sonindetectables con las tcnicas microbiolgicas decultivo convencionales.40,51,52 Estas limitantes en lastcnicas de cultivo se superan con el desarrollo de

herramientas moleculares, que permiten detectar eidenticar bacterias basndose en la secuenciacinde la diversidad del gen ARNr 16S. Gracias a estastcnicas, los conocimientos sobre el desarrollo y lasmodicaciones de la composicin de la fora microbianaintestinal han tenido avances importantes en losltimos aos. Recientemente, anlisis logenticosde la subunidad 16S del gen ARN proveniente delTGI de cerdos, revelaron una poblacin microbianamuy compleja, cuyas especies bacterianas no han sidocaracterizadas en su mayora.53 Estos autores reunieronuna biblioteca con 4 270 secuencias clonadas del genARN 16S, representando 375 lotipos procedentes del

leon, ciego y colon de cerdos entre 12 y 18 semanas devida. Estas miles de especies de bacterias del TGI, queconorman un ecosistema complejo, juegan un papelimportante en el bienestar global del animal,54 sobretodo en la salud intestinal, previniendo la colonizacinde microorganismos potencialmente patgenos.49

Al nacer, los lechones quedan expuestos a losmicroorganismos del ambiente que les rodea, y elcontacto con la fora microbiana materna y sus hecesen la maternidad, introduce bacterias que colonizansu tracto digestivo.54 Estas bacterias buscan el nichoms adecuado donde compiten e interaccionanentre s, constituyendo nalmente una poblacinrelativamente estable y compleja, que representa lamicrobiota intestinal normal.54 En el lechn lactantelas bacterias dominantes en el estmago e intestinodelgado suelen ser lactobacilos y estreptococos, ambosgrupos estn bien adaptados a utilizar el sustratolcteo disponible.54 La microbiota que se desarrollaen el intestino grueso poco despus del nacimiento,est constituida por una extensa y variada seleccinde bacterias mayoritariamente anaerobias estrictas,incluyendo bacteroides, bdobacterias, eubacterias,estreptococos y lactobacilos, mientras que en menordensidad pueden encontrarse otros microorganismos,

como las enterobacterias; normalmente, el gnerobacteroides es el ms numeroso y puede representarms de 30% del total.55 La fora microbiana normalque se establece despus del nacimiento, interactacon los sistemas digestivo e inmunolgico del cuerpoy sus actividades pueden ser bencas o dainaspara el husped.7 La colonizacin de los dierentescompartimentos del intestino por bacterias comensalesespeccas, particularmente por medio de la asociacin

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diarrhea is estimated;37 this index may be expressed bythe ollowing equation:

DSI = dFC/Pe

where:DSI= Diarrhea severity index.dFC= Daily ecal consistency grade.

Ep= Experimental period (days).

Diarrhea incidence is measured taking intoaccount the number o days in which it is present. Ingeneral, it increases between the rst and third weekpost-weaning.18 Diarrhea severity increases during thelast days o the rst week post-weaning,3,58 and duringthe second week post-weaning,10 notwithstanding theconsumed diet as it can be observed in Figure 2.

Probiotics, prebiotics and post-weaningdiarrheas

Probiotics and prebiotics are considered unctionaleed since they are compounds that have positiveeects over one or several unctions o the organismand promote animal wellbeing.59 Probiotics aredened as products that contain a specic, viablemicroorganism in sucient amount that due toimplantation or colonization alters microfora o acompartment o the gastrointestinal tract o the host,causing a benecial eect;60 probiotics have gainedpopularity as ood ingredients that are unctional evenor humans.9 Their eects on human health have beenstudied under several conditions, although results arestill not consistent, yet their ecacy has been identiedin the reduction o lactose intolerance signs, durationo several types o diarrheas, bacterial enzyme activityand in stimulating the immune system.61Positive eectso probiotic use in piglet eeding is maniested in theintestinal microbiota balance, intestinal epitheliumintegrity, maturation o tissues associated with thedigestive tract and their neuroendocrinous unction.62Inclusion o bacterial cultures (probiotics) in eed wasone o the rst alternatives used to replace antibiotics inanimal eeding.9 Post-weaning diarrhea control eectdepends on the used microorganism.7 A reduction inpiglet diarrheas was observed when a mixture o our

lactobacilli isolated rom weaned piglets was used;63

and the same happened whenE. coliNissle strain 1917was used.64 Yet, with the use o yeast in piglet eed therewas no observable reduction in diarrhea incidence.65

Prebiotics are another interesting alternative tosubstitute antibiotics or the reduction o incidenceand severity o diarrheas. Prebiotics are non-digestibleeed ingredients that have a benecial eect on thehost, since they stimulate selectively growth or activity

con el moco o de la adhesin a las clulas epiteliales,sirve como la primera barrera de deensa contraorganismos invasores o sustancias txicas presentes enla dieta. Al momento del destete, en un corto periodoocurren cambios en la composicin de la microbiotaintestinal del lechn en trminos de cantidad ycalidad, la cual evoluciona a una compleja y establecomunidad.52 El desarrollo de la microbiota intestinal

es un proceso gradual y secuencial que depende deactores nutricionales y no nutricionales.52,56 Se hainormado57 que la composicin de la microbiotaintestinal de los lechones diere entre individuos, auncuando los animales consuman la misma dieta.

Incidencia y severidad de las diarreasposdestete

En los trabajos experimentales realizados, la incidenciay la severidad de las diarreas se determinan mediantela apreciacin visual de la consistencia de las heces. Lamayora de las veces se emplea una escala, en la cual

se atribuyen calicaciones del 0 al 3.37 El valor 0 indicaheces normales, por tanto, la no existencia de diarrea;el valor 1 describe una diarrea ligera, pastosa; el valor2, una diarrea moderada, semi-liquida; y el valor 3 unadiarrea severa, muy lquida. La calicacin diaria sesuma durante el periodo experimental y se calculael ndice de severidad de la diarrea.37 Este ndice sepuede expresar a partir de la siguiente ecuacin:

ISD = CFd/Pe

Donde:ISD= ndice de severidad de la diarrea.CFd= Calicacin de la consistencia ecal diaria.Pe= Periodo experimental (das).

La incidencia de diarrea se mide en uncin delnmero de das en que se presenta. En general, estase incrementa entre la primera y tercera semanaposdestete.18 La severidad de las diarreas aumenta enlos ltimos das de la primera semana posdestete,3,58yen la segunda semana posdestete,10 sin importar la dietaconsumida, como se puede observar en la Figura 2.

Probiticos, prebiticos y diarreas

posdesteteLos probiticos y los prebiticos se consideran ali-mentos uncionalesal ser compuestos que tieneneectos positivos sobre una o varias unciones delorganismo y propician bienestar en el animal.59 Losprobiticos se denen como productos que contienenun microorganismo especco, viable y en cantidadsuciente, que por implantacin o colonizacin

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altera la microfora de un compartimiento del tractogastrointestinal de un hospedero, causando eectobenco.60 Los probiticos han ganado popularidadcomo ingredientes alimenticios uncionales inclusopara humanos.9 Sus eectos en la salud humanahan sido estudiados bajo varias condiciones, sintodava presentar resultados consistentes, pero se haidenticado su ecacia para reducir las seales de

intolerancia a la lactosa, la duracin de varios tiposde diarreas, la actividad de enzimas bacterianas y paraestimular el sistema inmune.61 Los eectos positivos deluso de probiticos en la alimentacin de lechones semaniestan en el balance de la microbiota intestinal, enla integridad del epitelio intestinal en la maduracin delos tejidos asociados al tracto digestivo, y en su uncinneuroendcrina.62 La inclusin de cultivos bacterianos(probiticos) a los alimentos ue una de las primerasalternativas usadas para reemplazar los antibiticosen la alimentacin animal.9 Su eecto en el control delas diarreas posdestete depende del microorganismoutilizado.7 Se observ una disminucin en la incidencia

de diarreas en lechones cuando se emple unamezcla de cuatro lactobacilos aislados de lechonesdestetados,63 al igual que cuando se utilizE. colicepaNissle 1917.64 Sin embargo, con el uso de levadurasen la alimentacin de lechones no se observ unadisminucin en la incidencia de diarreas.65

Los prebiticos son otra alternativa interesante parasuplir los antibiticos que disminuyen la incidencia yseveridad de las diarreas. Aqullos son ingredientesalimenticios no digestibles que aectan bencamenteal hospedero, pues estimulan de orma selectiva elcrecimiento o la actividad una bacteria o de un nmerolimitado de bacterias del colon, mejorando su salud.66Los prebiticos son sustratos para microorganismosbencos (bidobacterias y lactobacilos, entreotros), y pueden ser usados para controlar diarreasposdestete.9,59 Los prebiticos pertenecen a ungrupo muy variado de carbohidratos representadospor oligosacridos, como la inulina y oligoructosa,o polisacridos non amilceos, los cuales puedenaectar la ermentacin del tracto gastrointestinal y sumicrobiota.66 Los eectos de los carbohidratos sobreel tracto gastrointestinal y las poblaciones de E. coli, yconsecuentemente sobre la incidencia de colibacilosis,parecen estar asociados al tipo de carbohidratos

(solubles o insolubles; polisacridos u oligosacridos)presente en la dieta.11 Las poblaciones bacterianas deltracto gastrointestinal de lechones recin destetadosueron signicativamente modicadas por el consumode dietas con pulpa de remolacha, inulina, lactulosa yalmidn de trigo.52

Dietas bajas en protena cruda y diarreas

o a bacteria or a limited number o colon bacteria,

improving animal health.66 Prebiotics are substratesor benecial microorganisms (bidobacteria andlactobacilli, among others), and they may be used tocontrol post-weaning diarrheas.9,59 Prebiotics belongto a varied group o carbohydrates represented byoligosaccharides, such as inulin and oligoructose,or non-amylaceous polysaccharides, that can aectermentation within the gastrointestinal tract andits microbiota.66 Eect o carbohydrates on thegastrointestinal tract and E. coli populations andthereore on colibacillosis incidence, seem to beassociated with the type o carbohydrates (solubleor insoluble; polysaccharides or oligosaccharides)present in the diet.11 Bacterial population o thegastrointestinal tract o newly weaned piglets weresignicantly modied by the consumption o dietswith beet pulp, inulin, lactulose and wheat starch.52

Diets low in crude protein andpost-weaning diarrheas

Post-weaning diarrheas (PWD) are considered to bewithin an important group o gastrointestinal diseasesin swine, with a multiple actor etiology, alreadymentioned above (Figure 1) and associated with

enterotoxigenic E. coli (ETEC) prolieration.2,11,21,22

I antibiotics are not added to initiation diets duringthe immediate period ater weaning, they must beormulated with barely 17% to 18% crude protein(CP) to avoid intestinal malunction and diarrheaincidence.67 Post-weaning diarrhea incidence andseverity are higher in piglets ed diets with high levelso CP. (Figures 2 and 3).10,18,37,68 When CP level isincreased in diets rom 13% to 23%, eces fuidity was

Figura 2. ndice de severidad (IS) de diarreas durante los primeros14 das posdestete en lechones alimentados con dietas con un alto

(DAPC) o bajo nivel de protena cruda (DBPC).10

Figure 2. Severity index (SI) o diarrheas during the rst 14 daysater weaning o piglets ed with high crude protein level (HCPL)

or low level (LCPL).10

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increased and there was a reduction o its dry matter,increasing the risk o post-weaning enteric disordersincidence.10 Heo et al.68 concluded that diets low in CP(17.3% versus24.3 % CP) reduced diarrhea incidenceduring the rst seven to ten days ater weaning. Similarresponses were observed using diets with 23.6% and17.6% CP,18 or reducing diet CP rom 23.1% to 17.2%(Figure 3).69 Feces with less liquid and higher amount

o dry matter were obtained in piglets ed diets withmore restriction in CP (rom 20% to 12% CP).3 Inour weeks-old piglets challenged orally with ETEC(E. coli0149 239/03) on the third day post-weaning,consuming a diet with 13% o CP, had eces rmnesssignicantly increased six days ater the challenge,when compared to piglets ed with a 23% CP diet.2

A probable explanation to the dietary CP leveleects on incidence and severity o PWD, is that dietslow in CP (17%) in relation to diets high in CP (23%or more) help maintain intestinal health throughthe reduction o ureic nitrogen levels in plasmaand toxic microbial metabolite production such as

ammonia, which indicates a reduction in proteinermentation.16,19,69 Nevertheless, there are studiesthat indicate that dietary CP level does not aectPWD incidence. Reduction o CP level rom 22.4% to16.9% did not reduce diarrhea presentation;15 it wasalso observed that the presence o diarrheas and ecesconsistency was not aected by the level o CP in thediet (24% and 20%).17 Authors o this study believethat the good sanitary status o the experimentalpiglets, together with a low exposure to pathogenicbacteria could have contributed to the low incidenceo PWD during the rst 14 days post-weaning and thelack o response to dietary CP level reduction.

Based upon the above, it was concluded thatPWD are due to a combination o actors related tophysiological and immunological conditions o theGIT, as well as the chemical characteristics o initiationdiets and their eect on intestinal commensal and

posdestete

Las diarreas posdestete (DPD) estn consideradasdentro de un grupo importante de enermedadesgastrointestinales en los cerdos, con una etiologamultiactorial, mencionada anteriormente (Figura 1) yasociada con la prolieracin deE. colienterotoxignica(ETEC).2,11,21,22 Durante el periodo inmediato al

destete, si no se adicionan antibiticos a las dietasiniciadoras, es necesario que stas se ormulen conapenas 17-18% de protena cruda (PC) para evitarel mal uncionamiento intestinal y la incidencia dediarreas.67 La incidencia y la severidad de las diarreasposdestete son mayores en lechones alimentados condietas altas en PC (Figuras 2 y 3).10,18,37,68 Al elevar elnivel de PC de las dietas de 13% a 23%, se observun aumento en la fuidez de las heces y disminucinde su materia seca, incrementando el riesgo deincidencia en desrdenes entricos posdestete.10 Heoet al.68 concluyen que dietas bajas en PC (17.3% contra24.3% de PC) disminuyen la incidencia de diarreas enlos primeros 7-10 das posdestete. Respuestas similaresse observaron utilizando dietas con 23.6% y 17.6% dePC,18 o reduciendo la PC dietaria de 23.1% a 17.2%(Figura 3).69 Con una mayor restriccin de la PC dietaria(de 20% a 12% de PC)3 tambin se consignaron hecesmenos lquidas y con un mayor contenido de materiaseca en los lechones alimentados con la dieta baja enPC. Se ha observado2 que en lechones destetados a lascuatro semanas de vida y desaados va oral con ETEC(E. coli 0149 239/03) en el tercer da posdestete, elconsumo de una dieta con 13% de PC increment larmeza de las heces tres de manera signicativa a seis

das despus del desao en comparacin con lechonesalimentados con una dieta con 23% de PC.Una probable explicacin a los eectos del nivel

de PC dietaria sobre la incidencia y severidad de lasDPD, es que dietas bajas en PC (17%) en relacin adietas altas en PC (23% o ms) ayudan a mantenerla salud intestinal a travs de la reduccin del nivelde nitrgeno ureico en plasma y de la produccin demetabolitos microbianos txicos como el amoniaco,lo cual indica una reduccin en la ermentacin deprotenas.16,19,69 No obstante, hay trabajos que sealanque el nivel de PC dietaria no aecta la incidenciade DPD. La reduccin del nivel de PC de 22.4% a

16.9% no disminuy la presentacin de diarreas;15tampoco se observ que la presencia de diarreasy la consistencia de las heces uese aectada por elnivel de PC de la dieta (24% y 20%).17 Estos autoressuponen que el buen estado sanitario de los lechonesexperimentales, adems de la baja exposicin abacterias patognicas, pudieron contribuir a la bajaincidencia de DPD durante los primeros 14 dasposdestete y a la alta de respuesta a la reduccin del

Figura 3. Eecto del nivel de protena cruda (PC) dietaria sobreel ndice de severidad (IS) de las diarreas en lechones durante losprimeros 14 das posdestete.69

Figure 3. Eect o crude protein (CP) level in the diet on severityindex (SI) o piglet diarrheas during the rst 14 days ater weaning.69

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pathogenic microbial fora balance. Use o probioticsand prebiotics in initiation rations represent analternative or the replacement o antibiotics in thecontrol o PWD. Impact o dietary CP concentrationon post-weaning diarrhea is non-conclusive, sinceresults ound by dierent authors are contradictory.Nevertheless, there are important evidences that pigletdiets ree o antibiotics, the use o low concentration

o protein, help intestinal integrity during the rsttwo weeks ater weaning. This is achieved through thereduction o plasma ureic nitrogen and toxic microbialmetabolite production which indicates a reduction inprotein ermentation. It is probable that the additiono prebiotics or probiotics to diets with a low levelo CP may generate results positive or the intestinalhealth o piglets and reduction in the use o antibioticsin initiation diets.

Referencias

nivel de PC dietario.Con base en todo lo anterior, se concluy que las DPD

se deben a una combinacin de actores relacionadoscon las condiciones siolgicas e inmunolgicas delTGI, y tambin con las caractersticas qumicas delas dietas iniciadoras y su eecto en el equilibrio de lafora microbiana intestinal, comensal y patognica.El uso de probiticos y prebiticos en las raciones

iniciadoras representa una alternativa para reemplazarlos antibiticos en control de las DPD. El impacto dela concentracin de PC dietaria sobre la incidenciade las diarreas posdestete no es concluyente, pueslos resultados encontrados por dierentes autoresson contradictorios. Sin embargo, hay evidenciasimportantes de que en dietas para lechones libresde antibiticos, el uso de bajas concentraciones deprotena ayuda a mantener la integridad intestinal enlas dos primeras semanas posdestete; esto a travs de lareduccin del nivel de nitrgeno ureico plasmtico yde la produccin de metabolitos microbianos txicoscomo el amoniaco, lo que indica una reduccin en la

ermentacin de protenas. Es probable que la adicinde prebiticos o de probiticos a dietas con un bajonivel de protena dietaria pueda generar resultadospositivos para la salud intestinal de los lechones ydisminuir el uso de antibiticos en las dietas iniciadoras.

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