4-Crecimiento compensatorio [Modo de compatibilidad] · 2015. 1. 20. · CRECIMIENTO COMPENSATORIO Crecimiento compensatorio se refiere a la tendencia general a recuperar las ...

CRECIMIENTO COMPENSATORIO

Crecimiento compensatorio se refiere a latendencia general a recuperar lascaracterísticas normales de peso o curva decrecimiento después de un periodo desubnutrición.

El crecimiento compensatorio es afectado poruna serie de factores: propios del animal ynutricionales.

Entre los factores propios del animal destacan:- grado de madurez al inicio de la subnutrición: En general, al

animal joven le es más difícil exhibir un crecimientocompensatorio que al adulto.

Una restricción de proteínas en animales jóvenes puedecausar un daño irreparable. La reserva proteica en músculoes poca; en consecuencia el tejido puede agotarse, ya quelas reservas de grasa son relativamente bajas a esta edad.En los animales adultos se puede restringir la proteínadentro de ciertos límites, ya que las reservas son mayores.

La máxima susceptibilidad, a la restricción se halla alrededordel nacimiento. Para el bovino la edad mínima derestricción está entre los 6-8 meses.

- depósitos adiposos al inicio de la subnutrición: un animal congran cantidad de reservas puede soportar mejor el periodode subnutrición. Por ello el grado de crecimientocompensatorio dependerá del nivel de depósitos grasos delanimal.

- esquema y duración de la recuperación: No sólo la cantidad sinotambién la calidad del alimento disponible determinan lamagnitud de la recuperación del animal. Muchas veces elperíodo de recuperación no es lo suficientemente amplio, y estodeterminará más tiempo para que los animales alcancen el pesode faena. Si la ración entre uno y otro período es diferente, elestímulo parece ser mayor.

El nivel de realimentación es sumamente importante, siendonecesario un alimento de alta calidad a fin de maximizar larespuesta compensatoria. La digestibilidad de la materia seca nodeberá ser inferior a 70-75 %. En términos energéticos, estoequivaldría a 2,8 Mcal EM/kg materia seca.

Manteniendo las ganancias dentro de los limites indicados, esposible esperar ganancias entre 15 y 20 % superiores a losanimales que han ganado peso en forma continuada.

Las ganancias de peso al principio de la realimentación sonmáximas y van decreciendo en el tiempo. Los animales másrestringidos dentro de los límites anteriormente citados son losque mayor aumento de peso experimentan durante larecuperación. Se pueden utilizar en la realimentaciónestimulantes del crecimiento para maximizar la respuestacompensatoria.

-genotipo: hay escasa información sobre la diferentecapacidad de las razas o especies a recuperar elpeso tras un periodo de subnutrición. Elcrecimiento compensatorio se manifiesta de formasimilar en todos los animales domésticos. Peroexisten dentro de cada especie razas cuya edadde maduración puede diferir notablemente, lo quehace que a una misma edad cronológica hayadistintas edades fisiológicas, siendo evidente quela respuesta a una situación de penuria estarácorrelacionada con el estado fisiológico del animal.

- cambios en la tasa metabólica y utilización de losnutrientes: hay diferencias entre especies en lareducción de la tasa metabólica durante periodosde restricción y aumento de la utilización de losalimentos en la fase de realimentación.

Factores nutricionales- Duración e intensidad de la subnutrición: es difícil

diferenciar el efecto de la duración y de laintensidad. Wilson et Osburn (1960) clasifican elperiodo de subnutrición en tres categorías:

1) restricción severa con pérdida de peso vivo2) restricción media con mantenimiento del peso vivo3) restricción escasa con un crecimiento inferior al

normalEl grado de recuperación aumenta conforme la

restricción fue menos severa, pero el grado delcrecimiento compensatorio mostrado en la primeraparte del periodo de recuperación es mayorconforme la restricción es más severa.

En casos de periodos muy largos de subnutriciónparece que se reduce o desaparece la capacidadde recuperación.

- composición del alimento durante la subnutrición:hay pocas evidencias de la importancia del nivelde proteínas o de energía durante la restricciónen la respuesta del crecimiento compensatorio. Aefectos prácticos, en los periodos de subnutriciónlo que se produce es una disminución en lacantidad de alimento, pero éste no suelepresentar una gran desbalance en suscomponentes.

- ingesta durante la realimentación: de todos losfactores que pueden influir en el crecimientocompensatorio, el aumento del apetito o ingestaes el más importante.

MECANISMOSEl animal logra su crecimiento compensatorio

por tres mecanismos:

-Prolongación del período de crecimiento.

-Incremento en el ritmo de ganancia de peso.

-Aumento del apetito.

MECANISMES ET CONSEQUENCES DE LA CROISSANCE COMPENSATRICE CHEZ LES RUMINANTS

L'alternance, volontaire ou non, de périodesd'apports alimentaires réduits et élevés engendrechez les animaux un phénomène de croissancecompensatrice. Plus particulièrement, l'influencede phases de restriction et de réalimentation sur laqualité finale des produits est un aspect novateurdes recherches menées dans ce domaine.

Par ailleurs, les mécanismes hormonaux liés à lacompensation sont dorénavant mieux connus. Ilsgouvernent l'orientation des métabolismesénergétique et protéique vers l'accroissement del'accrétion protéique pendant la croissancecompensatrice.

L'influence de la compensation sur la composition corporellefinale des animaux est faible, même si certains auteursdécrivent des animaux plus maigres à la fin d'une phasede compensation. En ce qui concerne les caractéristiquesdes muscles, les changements induits par une restrictionalimentaire sont souvent réversibles et annulés par lacompensation. Néanmoins, certaines études montrent uneamélioration de la qualité sensorielle finale de la viande,plus particulièrement de la tendreté.

Ces résultats sont à nuancer, mais justifient l'intérêt portéaux études reliant croissance discontinue etcaractéristiques du muscle et de la viande. Desdéveloppements futurs et des prolongements de cesrecherches sont envisagés et mis en perspective

Figure 1. Evolution des poids lors d'une croissance continue oudiscontinue. L'index de compensation est calculé à partir de l'écart depoids entre les deux types de croissance avant et après compensation

(d'après Hornick et al 2000).

Facteurs influençant la croissance compensatrice

Age à la restriction: Lorsque la restriction intervient avant le sevrage,les veaux ont une faible capacité de compensation, quel que soit leniveau de restriction imposé (revue de Berge 1991). Chez les ovins,Allden (1968) a montré que des animaux soumis à une restrictionalimentaire au cours des six premiers mois de leur vie rattrapaientleur retard en beaucoup plus de temps (56 mois) que ceux restreintspendant leur second semestre de croissance (11 mois decompensation). Reardon et Lambourne (1966) ont mis en évidenceune période butoir au-delà de laquelle les ovins ne compensentplus : ils ont observé une compensation entre 3 et 9 mois, mais plusentre 9 et 13 mois. Quelle que soit l'espèce, les animaux peuventcompenser pendant une large période une fois que l'âge critiqueinitial, situé après le sevrage, est passé. En revanche, unerestriction précoce, appliquée lorsque le développement des tissusosseux ou musculaire est prépondérant, peut compromettre lacroissance ultérieure des animaux. Par ailleurs, la capacité decompensation des animaux diminue à mesure qu'ils se rapprochentdu stade adulte

Nature de la restriction: La croissancecompensatrice se produit aussi bien après unerestriction énergétique que protéique. Il estsouvent difficile de découpler les apportsénergétiques et protéique chez les ruminants,même si Drouillard et al (1991) ont comparé l'effetde la nature de la restriction sur la croissanceultérieure de bœufs. Ils n'ont pu mesurer aucunedifférence significative dans les performancespendant la période de finition entre deux lotsd'animaux ayant subi une restriction de sévéritéidentique mais de nature différente. Lacompensation était toutefois influencée plusfortement par la sévérité et la longueur de larestriction lorsque celle-ci concernait l'énergieapportée

Sévérité de la restriction: Le tableau 1 regroupe desvaleurs de vitesse de croissance de bovins pendant lesphases de restriction et de réalimentation. D'une manièregénérale, la réponse compensatrice des animaux estd'autant plus importante que la restriction imposée estforte, pour un même type d'animal. Il semble cependantexister un optimum pour l'index de compensation enfonction de la sévérité de la restriction. Les donnéesmesurées chez des bœufs Angus par Saubidet et Verde(1976) (figure 2) montrent en effet que l'index decompensation est maximal pour une croissance de l'ordrede 250 g/j pendant la phase de restriction. L'index decompensation est notamment plus faible qu'à l'optimumlorsque la croissance de ces animaux devient négative, cequi traduit une capacité de compensation plus faible.

Tableau 1. Durée de restriction et de réalimentation et

gain moyen quotidien mesurés chez des bovins

Figure 2. Evolution de l'index de compensation pour différentes croissancespendant la phase de restriction. Données de Saubidet et Verde (1976) pour desboeufs Angus. L'index a été calculé lorsque les animaux du lot témoin ontatteint l'objectif de poids fixé (450 kg).

Durée de la restriction : L'augmentation de la durée de larestriction, sans en modifier la sévérité, augmente lavitesse de croissance durant la phase de compensation.Graham et Searle (1975) ont montré que des moutonsmaintenus au même poids pendant 6 mois avaient unecroissance plus forte après réalimentation que ceux dont lepoids ne restait constant que pendant 4 mois. Cependant,d'après Drouillard et al (1991), la sévérité de la restriction aplus d'effet que sa durée sur la vitesse de croissancependant la compensation. Des bœufs ayant subi unerestriction énergétique sévère montrent peu d'écart decroissance pendant la réalimentation si la durée derestriction est longue ou courte (1,60 vs 1,46 kg/j). Aprèsune restriction peu sévère et courte, la vitesse decroissance compensatrice des animaux estsignificativement plus faible (1,09 kg/j).

Mode de réalimentation: La croissancecompensatrice se réalise souvent aupâturage. Le niveau d'alimentation estparticulièrement élevé au printemps car ilcoïncide avec la forte poussée de l'herbe.Assez logiquement, la croissancecompensatrice est d'autant plus forte que leniveau de réalimentation est élevé. Lors dela réalimentation, la nourriture doit doncêtre fournie ad libitum pour que le maximumde croissance ait lieu.

Mécanismes de la croissance compensatrice

3.1 / Modification de l'ingestionIl est connu qu'à la suite d'une période de restriction alimentaire, lesanimaux augmentent leur ingestion pendant la phase de réalimentation.Ainsi, Micol et Béranger (1981) ont estimé, sur la base d'une analyse dedonnées de la littérature, que les quantités de matière sèche ingérées pardes bovins restreints puis réalimentés, rapportées à leur poidsmétabolique (poids vif0,75), étaient accrues d'en moyenne 10 % pendantla phase de réalimentation par rapport à des animaux en croissancecontinue. L'analyse des résultats fait cependant apparaître de fortesvariations autour de la valeur moyenne : l'augmentation varie de 3 à 24 %suivant les expérimentations. Ces variations sont en partie liées à lasévérité de la restriction alimentaire, mais résultent aussi de différences dedéveloppement du tractus digestif pendant la phase de sous-alimentation.Ryan et al (1993a) ont constaté que l'écart de quantités ingérées, entredes bœufs en compensation et des témoins, ne s'établissait que 100 joursaprès la réalimentation et le passage à une alimentation à volonté. Cedélai dans l'augmentation des quantités ingérées pendant la compensationest attribuable au temps nécessaire à la restauration des capacités dutractus digestif, à la suite d'une restriction relativement sévère ayantentrainé une perte de poids. L'augmentation des quantités ingérées estdue principalement à un état d'engraissement plus faible des animaux encompensation (Forbes 1986).

3.2 / Modification des métabolismes énergétique et protéiquea / Conséquences d'une restriction alimentaireLa restriction alimentaire se traduit par une baisse des dépenses

énergétiques associée à une diminution du métabolisme de base et del'activité physique. Cette diminution des dépenses énergétiquesdépend de la sévérité de la restriction alimentaire, de sa durée etd'autres facteurs comme la race, le sexe et la composition corporelle.Des études ont montré chez les animaux restreints une économied'énergie exprimée par unité de poids de l'ordre de 13 à 20 % parrapport à des animaux alimentés au-dessus de l'entretien (Ortigues etDurand 1995). Les mêmes tendances sont retrouvées dans d'autresétudes, mais les résultats restent extrêmement variables.

La diminution des dépenses énergétiques globales peut s'expliquer parune diminution de la taille et du poids des tissus et/ou une diminutionde l'activité métabolique par unité de poids pour tout ou partie destissus. Malgré leur faible importance pondérale, le tube digestif, le foieet la peau participent pour environ 60 % des dépenses énergétiquesde l'organisme. Lors de la restriction alimentaire, les dépensesénergétiques, les débits sanguins et le poids des tissus splanchniquesdiminuent fortement. L'impact de la restriction alimentaire sur lesdépenses énergétiques musculaires apparaît à plus long terme et cesont les tissus splanchniques qui sont essentiellement responsablesdes modifications des dépenses énergétiques de l'animal entier.

Conclusion Il apparaît que la réponse compensatrice des animaux, à la

suite d'une restriction alimentaire, varie principalement enfonction de la durée et de la sévérité de cette restriction. Lacompensation s'effectue par le biais de plusieursmécanismes qui aboutissent à une augmentation du gainde poids de l'animal, en comparaison d'un organisme encroissance continue. Les dépenses énergétiques réduitespendant la phase de restriction restent relativement basseslorsque les apports sont augmentés. Lorsque le tractusdigestif des organismes a retrouvé son potentiel, l'ingestionest accrue en comparaison d'animaux ne compensant pas.Sous la dépendance de nombreux signaux hormonauxsynergiques, l'ensemble du métabolisme s'oriente vers uneaugmentation de l'accrétion protéique. A la suite de cettecroissance compensatrice, la composition corporelle desanimaux est variable. A même poids vif, les animaux sontsouvent soit plus maigres que des animaux en croissancecontinue, soit ne présentent pas de différence decomposition avec ces mêmes animaux.

Les recherches sur les effets d'une croissance discontinuesur les caractéristiques musculaires et la qualité ultérieurede la viande montrent des résultats variables suivant lesexpérimentations. Certaines études montrent que lacompensation peut avoir un effet positif sur la tendreté duproduit final. Les autres propriétés sensorielles de laviande apparaissent peu affectées par le type de conduite.

Ces travaux méritent d'être poursuivis afin de confirmer oud'infirmer les premières conclusions. Ils devront êtrecomplétés par l'étude de l'influence de la compensation surles qualités nutritionnelles de la viande. L'étude desmécanismes métaboliques et hormonaux doit êtreapprofondie, afin de mieux comprendre les processus àl'origine des phénomènes observés. L'ensemble de cespistes et des résultats qui en découleraient pourraitpermettre d'associer une amélioration objective de laqualité des produits avec une conduite des animauxcouramment répandue dans les élevages de type extensifet qui bénéficie de ce fait d'une image valorisante.Quoiqu'il en soit, l'intérêt économique de ce type deconduite, avec restriction hivernale de l'alimentation etutilisation optimale du pâturage, ne se dément pas.

EVALUACIÓN DEL CRECIMIENTO COMPENSATORIO COMO ESTRATEGIA DE

MANEJO EN VACUNOS DE CARNE A PASTOREO

Se evaluó el efecto de una restricción en la oferta de alimentosobre el crecimiento de vacunos de carne en pastoreo. 77toretes mestizos (Bos taurus x Bos indicus) de 1,5-2 añosde edad y 256,4 kg de peso. Partiendo de información depeso vivo desde 193 días antes del ensayo, durante 124días (agosto-diciembre) animales con balance nutricionalprevio positivo (n= 24; Control) o con una restricciónalimentaria previa (n = 16; RA) fueron asignados a potrerosque garantizaron una variación de peso vivo positiva hastafinalizar la evaluación y animales con balance nutricionalpositivo (n = 22; ARA) o con un evento de restricciónalimentaria previa (n = 15; RR). Durante los primeros 62días de evaluación con una restricción en la oferta debiomasa vegetal que garantizó una ganancia de pesoaproximada del 41% de la mostrada por el Control yposterior realimentación el resto de la experiencia.

Durante la fase de restricción, RR mostró unaganancia diaria de peso inferior a la del Control(0,342 vs. 0,793 kg/animal/d, respectivamente;P=0,001). Sin embargo, durante la fase derealimentación mostró superioridad en estavariable (1,107 vs. 0,875 kg/animal/d,respectivamente; P=0,07). Se evidencia que lamanipulación de restricciones en la oferta dealimento y el crecimiento compensatorio envacunos a pastoreo pueden ser estrategias paramaximizar la eficiencia de uso de recursosfibrosos, que permitirían manejar eficientementelas reiteradas condiciones de estrés nutricional aque son sometidos los rebaños vacunos bajocondiciones tropicales

REGULATION DU METABOLISME LIPIDIQUE DES TISSUS ADIPEUX ET MUSCULAIRES CHEZ LE RUMINANT. EFFETS

DU NIVEAU ALIMENTAIRE ET DE LA PHOTOPERIODE

Les effets respectifs de l'état nutritionnel et de la photopériodesur le métabolisme lipidique et le partage de nutriments entrele tissu adipeux et le muscle sont récapitulés chez leruminant, en particulier pour ce qui concerne l'expression desgènes spécifiant les enzymes lipogéniques et la lipoprotéine-lipase chez la vache et la brebis. La restriction alimentairediminue la synthèse de novo d'acides gras et l'activitélipoprotéine-lipasique dans les tissus adipeux des ruminantsadultes ou en croissance. Ces effets sont partiellement outotalement inversés par la réalimentation. Chez les ovins etles bovins adultes, l'activité lipoprotéine-lipasique estdiminuée par la restriction dans le muscle cardiaque, oxydatif,inchangée dans le muscle Longissimus thoracis, glycolytique,et augmentée par la réalimentation dans ces deux muscles.Les activités lipoprotéine-lipasiques du tissu adipeux et dumuscle de ruminant répondent donc dans le même sens àdes variations de l'état nutritionnel, contrairement auxdonnées généralement publiées chez le rat.

De plus, les taux d'ARNm de la lipoprotéine-lipase dans letissu adipeux et le muscle varient de manières identiques àson activité chez les différentes espèces, ce qui suggèreune régulation, au moins en partie, pré-traductionnelle del'expression du gène spécifiant cette enzyme. Laphotopériode exerce une influence directe sur l'activitémétabolique des tissus adipeux et musculaires de brebis.Ainsi, les capacités lipogéniques du tissu adipeux etl'activité lipoprotéine-lipasique du muscle glycolytique sontaugmentées par les jours longs. Inversement, lalipomobilisation est augmentée par les jours courts. Cesadaptations métaboliques sont probablement impliquéesdans les adaptations physiologiques des ovins auxvariations saisonnières des disponibilités alimentaires.

Reduced and Compensatory Growth: Endocrine andMetabolic Changes during Food Restriction and

Refeeding in SteersABSTRACT

Effects of food restriction, followed by refeeding, on energy and nitrogenmetabolism, growth rates and blood levels of hormones andmetabolites were studied in steers. During the restriction period, whichlasted for almost 5 mo, allowance for energy and nitrogen were close tomaintenance requirements. Heat production and growth rates weremarkedly lowered. In response to reduced food intake concentrations ofthyroxine (T4), 3,5,3'-triiodothyronine (T3), insulin (IRI), glucose and a-amino-acid nitrogen (AAN) were reduced, those of growth hormone(GH) and nonesterified fatty acids (NEFA) were elevated, whereas3,3',5'-triiodothyronine (rT3) and albumin were not different from levelsmeasured in nonrestricted animals. During refeeding heat productionand energy balances increased, nitrogen balances were transientlyelevated and the animals exhibited compensatory growth.

In response to refeeding, concentrations of T4,T3 and IRI increased withindays. In contrast, GH decreased whereas rT3 did not change Within 2 dof refeeding there was a rapid fall of NEFA, and an increase of glucose,and /3-hydroxybutyrate within 2 and 12 d, respectively. The datademonstrate the ability of growing ruminants to adapt rapidly tovariations in food intake by closely linked metabolic and endocrinechanges, which are associated with shifts in energy and nitrogenmetabolism and, finally, by reduced or compensatory growth.

Braunvieh steers (14 in experiment 1, and 12 in experiment 2)were raised mainly on hay and silage. At the start of thetrials the 1-yr-old animals were allocated to evenly weightedgroups. In experiment 1, after a 60-d adaptation period,seven control animals (group C) were fed a pelleted diet(10% hay and 90% concentrates) for an average dailygrowth rate of 800-900 g during the whole study. Sevenother animals (group RR), were fed a restricted amount ofanother pelleted ration (peanut extraction meal and straw)calculated to maintain their body weight. After 141 d ofrestricted feeding they were realimented with the same feedand at the same feeding level (on a metabolic body weightbasis, kilograms0.75) as the control animals. Experiment 2started with animals of the same age as in experiment 1.After the period of energy restriction, lasting for 151 d, theanimals were refed with loose hay and pellets consisting ofconcentrates (55%, higher energy density than inexperiment 1) and straw (45%, treated with 3% sodiumhydroxide).

A decrease of glucose levels, observed with increasing age innormally fed and in food-restricted animals, is well known inruminants.

A marked increase of circulating NEFA, observed on d 75 of theexperiment, may be a consequence of the mobilization ofreadily releasable fatty acids, or it indicates that the need forfat mobilization to bridge energy deficits is particularly high inearly stages of energy restriction.

Ketosis was apparently not a problem during the period ofreduced food intake since immediately before refeeding,circulating AAC and BHB were in the range for adequately fedsteers while it is known that steers react sensitively instarvation with increased levels of especially AAC and alsoBHB.

Low levels of circulating IRI during periods of food restrictionwere not unexpected. It probably facilitated catabolicprocesses such as fat mobilization and was presumablyresponsible for reduced protein accretion. The transientincrease of circulating IRI during the first days of refeedingmay have functioned as an overshooting signal for theinitiation of anabolic processes.

Circulating GH was elevated during food restriction andrapidly decreased during refeeding. Thus, the behaviorwas opposite to that of IRI.

The reduction of T4 and T3 levels, but not of FT4 and FT3fractions, during food restriction correspond toobservations made with sheep and with steers. Levels ofT3 were much more closely associated with shifts inenergy metabolism than T4

Differences in energy intake are considered to have beenprimarily responsible for metabolic and endocrinechanges, and for alterations in the growth rates seen inthis study. Although food composition was different in thefood-restricted as compared to the adequately fedanimals, this is assumed to have been of minorimportance

This study demonstrates rapid and coordinated endocrineand metabolic responses to alterations in food restrictionand refeeding.

Compensatory growth and carcass quality in growth-restricted and refed beef steers

ABSTRACT: Beef steers were fed in two phases 1) to determinethe relative importance of changes in DMI, gastrointestinaltract fill, energy expenditures, and composition of gain in thecompensatory growth phenomenon, 2) to compare the effectsof growth restriction due to ad libitum consumption of alowenergy (low-concentrate) diet to those of limited intake of ahigh-energy (high-concentrate) feed, and 3) to examinechanges in carcass composition and quality resulting fromdifferent types of growth restriction. During the growing phase(237 to 327 kg), steers were fed either a high- (C) or low- (F)concentrate diet. Diet F was available for ad libitumconsumption (FA) and diet C was available either for adlibitum consumption (CA) or on a limited basis (CL) to matchthe live weight gains by the FA group. During the finishingphase (327 to 481 kg), all steers received diet C, either for adlibitum consumption (CA) or restricted (CL) to 70% of theintake by the corresponding CA steers. Backfat thickness wasmarkedly reduced ( P < .001) by final feed restriction (7.4 and6.9 mm for CL-CL and FA-CL respectively), compared withCA-CA (12.6 mm).

Backfat also was lower in CL-CA (11.6 mm, P < .10) and FA-CA (9.9 mm,P < .05) than in CA-CA steers. Conversely, marbling scores were similaramong groups, except for the FA-CL steers, which had lower marblingscores than FA-CA and CL-CA steers ( P < .05). Higher DMI followinggrowth restriction were accompanied by increased rates of live weight(+54 and +27%) and empty body weight (EBW; +57 and +43%) gain forCL-CA and FA-CA steers, respectively, compared with CA-CA steers.Gain:feed (EBW basis) were improved in some restricted/refed groups(+30, +13, and +10%, for CL-CA, CL-CL, and FA-CA, respectively)relative to CA-CA. Increased DMI played a major role in thecompensatory gain response in both CL-CA and FACA groups.Maintenance requirement was reduced ( -17%) in CL-CA and increasedin the FA-CA group (+21%); both changes affected the magnitude ofcompensatory gain in those animals. In contrast, composition of gainhad little or no effect on the compensatory gain response. Programmedfeeding can be used to manipulate carcass quality, but lowconcentratefeeding during the growing phase may impair overall feedlotperformance.

CONCLUSIONSSteers recovering from growth restriction exhibited more

rapid (compensatory) growth upon refeeding.For both low-concentrate and limit-fed steers this was mainly

due to increased dry matter intake; steers limit-fedconcentrate also converted feed more efficiently duringthe finishing period than those previously fed a low-concentrate diet. Carcass fat content was unaffected, butfat distribution was altered so that growth-restricted/refedsteers had less subcutaneous and more internal fat.Programmed feeding can be used to alter carcass quality,but low-concentrate feeding during the growing phasemay impair overall feedlot performance.

Compensatory Growth in Dairy Heifers:The Effect of a Compensatory Growth Patternon Growth Rate and Lactation Performance

The objective of this study was to improve the efficiency ofgrowth and lactation performance of dairy heifers fed for astair-step growth pattern.

Twenty-four young Holstein heifers were randomly assignedto either control or test groups. The test group was fedaccording to a schedule of 3, 2, 4, 2, 5 and 2 mo in whichfeed intake was alternately 20% below or 25% aboverequirements.

Heifers that were subjected to the stair-step growth patterngained more body weight and consumed less dry matter,resulting in improved efficiency of growth compared withthat of controls (7.8% vs. 8.3%). First estrus, firstconception, gestation period, services per conception, andcalving difficulty (dystocia) were not affected by stair-stepgrowth.

Concentration of growth hormone in blood serumwas elevated during feed restriction for the testheifers; however, during refeeding, growthhormone was decreased compared with that in theblood serum of control heifers. Mammary tissuesobtained by biopsy from heifers in middle and latepregnancy were used for chemical compositionanalysis. Stair-step growth increased DNA, RNA,protein, the ratio of RNA to DNA, and the ratio ofprotein to DNA. Lipid decreased in the mammarytissue of test heifers in late pregnancy (9.5 mo).Heifers in the test group yielded approximately 9%more milk than did heifers in the control group.These results indicate that compensatory growthcan contribute to the improvement of growthefficiency and lactation performance.

In summary, the heifers on the compensatory growthregimen gained more BW and consumed less DM,resulting in better growth efficiency than the controls.Reproduction data were unaffected by the stair-stepgrowth pattern. Changes in dietary and nutrient densitypresented in a stair-step growth pattern altered thesecretion of growth hormone and insulin, hormones thatregulate mammary development.

Stair-step growth also increased DNA, RNA, protein, theratio of RNA to DNA, and the ratio of protein to DNA. Lipidcontent decreased in mammary tissue from test heifers inlate pregnancy (9.5 mo).

As a result, heifers from the test group yieldedapproximately 9% more milk than did controls. Our resultsindicate that a stair-step growth pattern can enhancegrowth rate and lactation performance.

COMPENSATORY GROWTH RESPONSE IN PIGS: Effects on growth performance, compositionof weight gain at

carcass and muscle level, and meat quality

ABSTRACT: A restriction/realimentation feeding strategy wasapplied to pigs to increase the age at market weight andfinal ADG, modify protein and lipid deposition rates atcarcass and muscle levels, and thereby improve eatingquality of the pork. A total of 126 Duroc × (Large White ×Landrace) pigs (females and castrated males) were used.At the average BW of 30 kg, within litter and sex, pairs oflittermates (blocked by BW) were randomly assigned to adlibitum (AL) feeding during growing (30 to 70 kg of BW) andfinishing (70 to 110 kg of BW) periods (AL, n = 56), orrestricted feeding at 65% of the ADFI of the AL pigs, on aBW basis, during the growing period and AL feeding duringfinishing (compensatory growth, CG; n = 56).

In each feeding regimen, 15 pigs were slaughtered at 70 kgof BW, and 41 pigs were slaughtered at 110 kg of BW.Additionally, 14 pigs were slaughtered at 30 kg of BW tocalculate tissue deposition rates. The CGpigs showeddecreased ADG (−35%, P = 0.001) during growing butincreased ADG (+13%, P = 0.001) during finishing (i.e.,compensatory growth) due to greater (P = 0.001) ADFI andG:F. Hence, CG pigs were 19 d older at 110 kg of BW thanAL pigs.

The CG pigs were leaner at 70 kg of BW than AL (e.g., 11.7vs. 13.5 mm of average backfat thickness for CG and ALpigs, respectively, P = 0.023), whereas the differenceswere reduced at 110 kg of BW (20.6 vs. 21.0 mm ofaverage backfat thickness for CG and AL pigs,respectively, P = 0.536). At 70 kg of BW, intramuscular fat(IMF) content of LM did not differ between CG and AL pigs(1.25 vs. 1.49%, respectively, P = 0.118), whereas CG pigshad less IMF in LM at 110 kg of BW (2.19 vs. 2.53% forCG and AL pigs, respectively, P = 0.034).

Feeding regimen influenced the composition of weight gain.From 30 to 70 kg of BW, feed restriction reduced (P =0.001) lean and adipose tissue deposition at the carcasslevel and protein and lipid deposition at the muscle level.From 70 to 110 kg of BW, the CG feeding strategyincreased (P = 0.016) deposition of adipose but not of leantissue at the carcass level. However, lipid and proteindeposition at the muscle level were not affected. Thus,realimentation promoted deposition of subcutaneous fatover IMF. Feeding regimen hardly affected technologicalmeat quality at 110 kg of BW. The CG feeding strategydecreased (P = 0.014) the meat juiciness score in relationto the decreased IMF but did not influence other sensorytraits. Elevated IMF content and improved pork qualitymight be achieved by modifying the onset or duration ofthe restriction and realimentation periods.

The objective to produce older pigs at commercial marketweight through feed restriction during growing andrealimentation during finishing periods was reached.Refed pigs expressed a compensatory growth during thefinishing period compared with ad libitum fed pigs. Duringrealimentation, composition of weight gain was modified(greater adipose than lean tissue deposition) at thecarcass level. Hence, carcass quality of compensatorygain pigs was comparable to those of ad libitum-fed pigsat live weight of 110 kilograms.

However, at muscle level, composition of weight gain wasnot modified. Consequently, the initial hypothesis ofincreased intramuscular fat deposition through increasedaverage daily gain and age at live weight of 110 kilogramscould not be verified. The restriction-realimentationfeeding strategy did not lead to improved meat eatingquality. It can be hypothesized that an elevatedintramuscular fat content in refed pigs, which wouldimprove pork quality, might be achieved throughforwarding the onset or modifying the duration ofrestriction and realimentation periods.

COMPENSATORY GROWTH IMPROVE MEAT TENDERNESS IN GILTS BUT NOT IN BARROWS

ABSTRACT: Compensatory growth is a phenomenon observed in pigs givenfree access to feed following a period of restricted feeding that results inincreased growth rates. Compensatory growth is believed to increaseprotein turnover and thereby the proteolytic potential at the time ofslaughter, leading to faster tenderization rates of meat. Nine litters of threegilts and three barrows were allocated within litter and gender to threedietary treatment groups. Pigs had ad libitum access to feed from d 28 toslaughter at d 140 (ALA) or were restricted to 69% ad libitum from d 28 to d80 or 90, and then given ad libitum access to the diet until slaughter at d140 (RA80 and RA90, respectively).

Pigs in the RA80 and RA90 treatment groups had a 9.7% higher (P < 0.001)fractional growth rate in the second feeding period than those in the ALAgroup. Growth rate was correlated to the activity of m-calpain (r = 0.37; P <0.01), β-glucuronidase (r = 0.48; P < 0.001), and cathepsins B (r = 0.47; P< 0.001) and B+L (r = 0.31; P < 0.04).

The LM of RA80-gilts received higher tenderness scores than the LM ofALA gilts, but tenderness scores were similar among barrowsregardless of treatment (gender × treatment; P = 0.02). Conversely,tenderness scores were higher for the biceps femoris of ALA barrowsthan either ALA gilts or RA90 barrows (gender × treatment; P = 0.02).Desmin and troponin-T degradation, as well as myofibrillarfragmentation index, of the LM were not (P ≥ 0.24) affected bytreatment. No dietary treatment effects were observed on the activitiesof -calpain (P = 0.15), m-calpain (P = 0.74), or calpastatin (P = 0.91) atslaughter. The cathepsin inhibitors, cystatins, tended to be increased(P = 0.06) in RA80 and RA90 pigs. Sarcomere length was longer (P =0.003) in the LM of gilts than barrows. Barrows in the RA80 group hadlower i.m. fat concentrations than ALA; however, no differences werefound in the LM of gilts (gender × treatment; P = 0.03). The underlyinghypothesis that compensatory growth leads to an increased proteolyticpotential at the time of slaughter could not be verified in this study.

Results obtained from this study suggest that acompensatory growth strategy used on gilts is one way ofincreasing the pork tenderness without compromisingeither slaughter weight or percentage of meat. In barrows,compensatory growth has no detrimental effecton LM tenderness; however, tenderness of other musclesmay be decreased by compensatory growth.

Feed quality restriction and compensatory growth ingrowing sheep: development of body organs

AbstractThe effects of feed quality restriction and the consequent

compensatory growth on body organ development wasmeasured in 56 crossbred Swifter (Texel X Flemish) malelambs born in March 1993 and weaned at 2 months of age.The ration was gradually changed to an experimental dietof grass straw (51 g crude protein (CP) per kg dry matter(DM) ad libitum) and 35 g kg-0.75 d-1 of mixed concentrate(173 g CP per kg DM) . At 3 months of age, animals wererandomly assigned to a restricted R or a control C group.Group R was subjected to feed quality restriction bywithholding concentrates from 3–6 months of age. A serialslaughtering procedure was used to determine changes inbody organ weights. At the beginning of the experimenteight lambs, thereafter every 3 weeks four lambs two pergroup , and finally eight lambs four per group wereslaughtered. Growth was modelled using a linear function.

Estimated parameters clearly indicated reduced growthduring feed quality restriction and compensation duringrealimentation. The carcass showed an earlier effect ofrestriction and realimentation compared to body weightBW. Non-carcass components showed a delay in growthafter restriction but had a similar trend to BW afterrealimentation. At the end of the experiment, the weight ofthe small intestine was higher in R group. No differenceswere observed for other organs between groups. Ingeneral, early maturing parts head, feet and visceralorgans have high priority for use of the available nutrientsin the blood stream and are affected less than the latematuring parts by feed quality restriction. Afterrealimentation, the responses are mainly related to theirreactions during restriction, i.e., the organs which are mostaffected and have the greatest reduction, respond quickerthan those which are less affected.

Effects of a compensatory growth strategy on sensory andphysical properties of meat from young bulls

The objective of the present study was to investigate thesensory properties, with special emphasis on tenderness, ofmeat from strategically fed young bulls (13 months of age)slaughtered when a plateau in protein turnover wasobserved. Twelve Holstein Friesian young bulls were dividedinto two feeding strategies. One group of young bulls (n = 6)were fed ad libitum throughout the rearing period (AD)whereas the second group (n = 6) was subjected to acompensatory growth feeding strategy (CO). Sensoryprofiling of beef longissimus dorsi (LD), semimembranosus(SM) and supraspinatus (SS) was performed in addition tophysical measurements (shear force)

and content of intramuscular fat of LD.

Through profiling LD and SS were found to haveenhanced texture and flavour properties when theyoung bulls were fed ad libitum during rearing.However, the SM samples were found to improve incharacteristics regarding texture and appearancewhen the young bulls had been fed compensatorily.Thus, compensatory feeding as a textureimprovement strategy proved to be highly dependanton muscle type.

Considering the different preparation methods usedfor meat from LD, SM and SS, compensatoryfeeding may be considered to have improved thetexture and elevated the eating quality where it wasmost relevant, namely in SM roasts

Mécanismes et conséquences de lacroissance

compensatrice chez les ruminants

L’alternance, volontaire ou non, de périodes d’apportsalimentaires réduits et élevés engendre chez les animaux unphénomène de croissance compensatrice. L’influence de lacompensation sur la composition corporelle finale desanimaux est faible, même si certains auteurs décrivent desanimaux plus maigres à la fin d’une phase de compensation.En ce qui concerne les caractéristiques des muscles, leschangements induits par une restriction alimentaire sontsouvent réversibles et annulés par la compensation.Néanmoins, certaines études montrent une amélioration de laqualité sensorielle finale de la viande, plus particulièrementde la tendreté.

EFFECT OF THE DEGREE AND DURATION OF EARLY DIETARY AMINOACID RESTRICTIONS ON GROWTH PERFORMANCE, CARCASS TRAITS,AND SERUM METABOLITES OF PIGS, AND PHYSICAL AND SENSORYCHARACTERISTICS OF PORK

The objective of this study was to investigate the effect ofdegree and duration of early dietary amino acid restrictionson growth performance, serum metabolites, internal organweights, and carcass traits of pigs, and subjective qualityscores and physical and sensory characteristics of pork. Forthe grower (G) and finisher 1 (F1) phases, 3 corn-soybeanmeal diets were formulated to contain 100, 80, or 60% of the1998 NRC total lysine recommendation (100G, 80G, or 60G,and 100F1, 80F1, or 60F1, for the G and F1 phases,respectively). For the finisher 2 (F2) phase, a common corn-soybean meal diet was formulated to satisfy the 1998 NRCtotal lysine recommendation.

Thirty gilts and 30 castrated males (2 gilts or 2 castrated males/pen) wererandomly assigned to 5 dietary treatments [100G-100F1 (control), 80G-100F1, 80G-80F1, 60G-100F1, and 60G-60F1] when they weighed 22.7 ±0.3 kg. Pigs were switched to F1 and F2 diets when they weighed 50.7 ±0.4 and 79.9 ± 0.5 kg, respectively.

Pigs fed the 60G diet had lower (P < 0.05) ADG during the G phase andgreater (P < 0.05) ultrasound backfat (UBF) at the end of the G phasethan those fed the 100G diet, and ADG decreased linearly (R2 = 0.70; P <0.001) as the degree of amino acid restrictions increased, indicating thatthe effort to depress growth performance and alter body composition byearly dietary AA restrictions was successful. The ADG in pigs fed the60G-100F1 diets at the end of the G phase were lower (P < 0.05) thanthose fed the control G and F1 diets, TP was similar between the 2 groupsat the end of the F1 phase. Their ADG during the F1 phase and UBF atthe end of the F1 phase were, however, similar to those fed the controldiets. Feeding the 80G diet resulted in numerically depressed ADG duringthe G phase, but there was no difference in ADG during the F1 and F2phases or UBF at the end of F1 and F2 phases between the pigs fed the80G and 100G diets.

Overall, pigs fed the 80G-80F1 diets had similar ADG, but theyhad less (P < 0.05) lean gain (LG) than those fed the controldiets. Pigs fed the 60G-60F1 diets had clearly lower (P < 0.05)overall ADG and G:F and less (P < 0.05) LM area and LGcompared with those fed the control G and F1 diets. However,they had higher (P < 0.05) subjective marbling score than thosefed the control diets. Dietary treatments had no clear effect onother serum metabolites, carcass backfat, subjective color andfirmness scores, organ weights, or physical and sensorycharacteristics of pork.

The results of the present study indicated that pigs fed the 80G-80F1 diets may have exhibited compensatory growth in terms ofweight gain but not in terms of lean accretion. On the other hand,growth performance and carcass traits of pigs fed the 60G-60F1diets were clearly depressed, indicating that the amino acidrestrictions may have been too severe or too long or both. Earlydietary AA restrictions had no clear effect on physical andsensory characteristics of pork.