The goal of this research was to evaluate the effects of calf starter fermentation on rumen pH, metabolic adaptation of ruminal epithelia and growth of calves during the weaning transition. In study 1, calf starter consumption increased short chain fatty acid concentration in the rumen and changed expression of genes involved in ketogenesis and intracellular pH regulation but did not affect rumen pH. In study 2, decreasing dietary starch content did not increase rumen pH. However, feeding a calf starter that had the highest in situ dry matter disappearance lowered rumen pH without adversely affecting feed intake and growth of calves. These findings suggest that rumen epithelium can metabolically adapt to increased fermentation in the rumen at molecular level, and that sub-acute rumen acidosis may not adversely affect feed intake and productivity of dairy calves during the weaning transition. / Animal Science

The purpose of the study was to determine if mothers who breast-feed their babies for nine months and longer experience problems when weaning. This research also determines the type of problems and weaning practices used by those mothers. In this descriptive study, data was collected from 150 mothers by means of questionnaires and interviews. The subjects were mothers who breast-fed their children for nine months or longer, who attended antenatal and postnatal clinics at Coronation Hospital. Reasons for weaning were inter alia the belief that the baby was old enough to be weaned. The results revealed that 42 (31,34%) of the respondents experienced problems during weaning. The problems included, among others, guilt feelings in the mother. Mothers use harsh methods of weaning such as sending a child away to a relative. There is minimal involvement of health workers in the health education of mothers on weaning. / Health Studies / M.A. (Nursing Science)

Through stable isotope analysis of human tooth dentine, this thesis investigates breastfeeding and weaning patterns in relation to rickets in a sample of sub-adults (n=12) interred in the nineteenth century sub-adult cemetery located at the Church of the Trinitarias in Madrid, Spain. The main objectives of this research are to create early life feeding histories for each individual using dentine serial sectioning techniques and apply these histories to investigate the relationship between breastfeeding, weaning, and vitamin D deficiency. The early life feeding histories allows for the determination of the onset and complete age of weaning at an individual level. These stable isotope data are then used to estimate general trends in breastfeeding and weaning practices in nineteenth century Spain. The results of this study indicate that the onset age of weaning for most of the individuals in this sample was between 10 and 14 months of age. The age at which breastmilk consumption stopped entirely was more difficult to estimate, however, in individuals that did show evidence of completed weaning, it was estimated to occur around the age of three. These ages are slightly higher than those discussed in historical sources for nineteenth century Spain. When these results are compared to contemporaneous, more industrialized, European countries the comparison shows that the initialization of weaning occurred slightly later and was a more gradual process in this Spanish sample. The results also demonstrate that there is no direct relationship between weaning patterns and the occurrence of skeletal vitamin D deficiency. It may be that the high prevalence of vitamin D deficiency is linked with the nuances of breastfeeding and other biocultural variables, such as a lack of sun exposure, an inadequate weaning diet, or childcare practices. / Thesis / Master of Arts (MA)

This study investigated effects of diet and probiotic supplement on stress in Thoroughbred foals at weaning. Twenty foals, whose dams were paired by age and breeding date, then randomly assigned to one of two diets prior to parturition, were used. Two groups were maintained on mixed grass pastures and fed supplements, one high in sugar and starch (SS) and one high in fat and fiber (FF) that met or exceeded NRC requirements. Half the foals on each diet were fed a commercial probiotic (Probios) containing lactic acid bacteria, while the rest were given a placebo. Plasma, fecal samples and behavioral ethograms were collected for four days pre- and post-weaning, and an ACTH response test was administered 48 h post-weaning. Cortisol, lactate, IgG, IgA and a-tocopherol were analyzed in plasma, volatile fatty acids and pH in feces. Foals fed FF had higher concentrations of IgA (P = 0.006), IgG (P = 0.012) and a-tocopherol (P = 0.005). Butyric and valeric acid concentrations were higher in feces of SS but not FF foals (P = 0.052), which may reflect better adaptation to forage in FF foals. Foals supplemented with probiotic had higher fecal lactate (P = 0.002) and lower fecal acetate (P = 0.0003) concentrations, suggesting that the lactic acid bacteria survived to the hindgut. Probiotic supplementation did not appear to benefit foals at weaning. Supplementation with FF may improve immune status and encourage a more diverse intestinal microbial population, enabling foals to better cope with the physiological stresses of weaning. / Master of Science

No description available.

No description available.

Many critical clinical conditions result in respiratory failure and precipitate the use of mechanical ventilation for their management. A prolonged period of mechanical ventilation is costly for both the patient, in terms of adverse effects, and the health care service. Therefore, immediate liberation of the patient from mechanical ventilation and constitution of spontaneous breathing, a process called weaning, is vital. This daily lifesaving practice, on which nurses are taking an increasing role with the introduction of nurse-led protocols, can become complicated requiring the effective use of assessment information through decision-making processes to improve outcomes of care. Most literature on the field fails to address that weaning decisions are affected not only by the nature of the task but also by the characteristics of the decision-maker and the decision environment. This research aimed to study nurses' decision-making processes when managing the weaning of long-term ventilated patients and to explore the impact of the diverse elements of the clinical environment on this intricate practice. An ethnographic approach was used to compare weaning decision-making processes in two different culturally intensive care units (ICU). Participant observation was used to follow the weaning practices of 10 patients in a Scottish ICU and 9 patients in a Greek ICU admitted with respiratory failure due to pneumonia or COPD exacerbation. Nurses were observed in their daily weaning practice and participated in reflective interviews at the end of their shift to extrapolate how they used the information to make their decisions. Semi-structured interviews were, then, conducted with nurses, physiotherapists and medical staff to explore their perceptions on weaning practices and the factors that influenced their decisions and clinical practice. Data were analysed thematically and concept maps were developed from the reflective interviews to analyse nurses‟ decision-making processes. The concept attainment theory was used as a framework to understand nurses' thinking processes. Nurses in all ranges of experience demonstrated a similar decision-making skill, which signifies that this cognitive process is not always related to the level of experience and knowledge. Nurses' weaning care was organised around maintaining a balance of care under the 'wean as able' medical instruction. Inconsistency in the weaning decisions led to a variability of weaning approaches followed for each patient and to long periods of weaning inactivity. Various reasons, related to the working relationships, lack of nurses‟ accountability, lack of support and unstructured information flow, were responsible for the deficiency in sustainable and consistent weaning decisions. In both settings, there was lack of culture to foster a shared decision-making approach in weaning practice and encourage nurses' autonomy in decision-making. This study concluded with proposing a collaborative decision-making framework for weaning long-term ventilated patients, which will involve and appreciate the contribution of all members of the multidisciplinary team.

Two experiments examined growth performance and physiological measures of stress in pre- and postweaned Angus steers (313 ± 24.5 kg; n = 48/Exp.), where steers were fitted with (YD) or without (ND) an anti-suckling device (Exp. 1), or provided (YS) or not provided (NS) a grain supplement (Exp. 2) for 7 d and weaned by fenceline (FS) or total separation (TS). Steers in Exp. 1 were weighed and bled on d 0, 3, 7 10, 14, 21, and 42, and in Exp. 2, on d 0, 7, 10, 14, and 21 and provided a grain supplement on d 7-21. In Exp. 1, weight gain was not different (P = 0.74) between ND and YD steers during preweaning. The YD-FS steers lost weight (P = 0.01) by d 10 compared with YD-TS steers. Hematocrit (Hct) increased (P = 0.04) in YD but not ND steers on d 3. Neutrophil:lymphocyte ratio (N:L) increased (P < 0.01) in all steers by d 7. Cortisol values in YD-FS steers were higher (P < 0.05) compared with YD-TS steers on d 10 and 21. The ND-FS steers had higher (P = 0.04) interferon-gamma (IFN) concentrations on d 10 compared with all YD steers. Haptoglobin (HAP) values increased (P < 0.01) in all steers by d 3. The FS steers had higher (P < 0.01) ceruloplasmin (CER) values by d 10 than TS steers regardless of preweaning treatment. Ovalbumin-specific IgG increased (P < 0.01) in all steers 10 d following its administration. In Exp. 2, NS-TS steers lost weight (P < 0.01) between d 7 and 10 compared with the remaining steers. The YS steers had higher cortisol, N:L and CER on d 7 compared with NS steers. Moreover, NS steers had higher (P < 0.01) Hct on d 10 than YS steers. Based upon physiological and growth performance data, it may be concluded that use of an anti-suckling device prior to weaning does not improve the animals’ well-being and, providing a grain supplement beginning 7 d prior to weaning may temper the animals’ stress response due to weaning when total separation is employed.

L'objectiu de la present tesis fou estudiar si la incorporació d'ingredients fibrosos a la dieta de garrins recent deslletats, era una bona estratègia per minimitzar els desordres intestinals que normalment ocorren durant l'etapa post¬deslletament, i d'aquesta manera facilitar l'adaptació digestiva dels animals en les següents etapes de creixement. Per aconseguir aquest objectiu, es dissenyaren quatre proves (capítols 4 a 7) experimentals.En la Prova 1 (Molist et al., 2009a), primer de tot volíem confirmar uns resultats preliminars obtinguts en una prova anterior on s'havia observat un major creixement dels animals quan una font de fibra insoluble (segó de blat, WB) fou introduïda en una dieta de garrins post-deslletament. Al mateix temps, també volíem analitzar si aquest tipus de fibra insoluble era adequada per aquest període de creixement dels animals, o si per contra, era més interessant incorporar un tipus de fibra soluble (com la polpa de remolatxa, SBP). L'objectiu de l'estudi era explorar l'efecte d'incloure dos tipus diferents de fonts de fibra (WB, insoluble i SBP, soluble) sobre el creixement, les característiques físico-químiques de la digesta i l'activitat metabòlica i la composició de la microbiota intestinal. Els resultats mostraren que la fermentació intestinal fou baixa durant la primera setmana post-deslletament. L'addició de WB o WB i SBP en la dieta incrementaren la fermentació intestinal i la concentració d'àcid butíric en la digesta cecal juntament amb una reducció de la població d'enterobactèries en les femtes. La conclusió de l'estudi fou que el consum d'un tipus de fibra insoluble durant els primers dies després del deslletament (ja sigui WB o WB-SBP) modifica les característiques físico-químiques de la digesta i afecta la colonització microbiana a l'intestí gros. També especularem que els efectes observats amb la inclusió de WB podrien està relacionats amb: 1.- canvis en les característiques físico-químiques de la digesta, tals com una majora capacitat de retenció d'aigua (WRC) i una major fermentació de la digesta intestinal, 2.- un efecte físic relacionat amb la mida de partícula gran o 3.- una reducció del temps de trànsit de la digesta intestinal. En la Prova 2 (Molist et al., 2009b), es volia confirmar la reducció de la població d'enterobactèries promoguda pel WB, i la seva capacitat per reduir els desordres digestius front a una infecció experimental amb E. coli K88. A més a més, es volia clarificar si aquest efecte observat amb la introducció de WB en la dieta estava relacionat amb la seva mida de partícula. Els resultats obtinguts confirmaren que la inclusió de WB reduïa la població de E. coli en la digesta ileal, i encara més interessant, també reduïa l'adhesió del E. coli K88 a la mucosa ileal. Al mateix temps, el WB amb mida de partícula grollera reduí la diversitat de la microbiota intestinal en comparació amb el WB molturat. La tercera prova (Prova 3, Molist et al., 2010a) fou dissenyada per esbrinar si els efectes positius del WB sobre la microbiota intestinal es devien a un efecte del WB sobre el trànsit intestinal dels animals. La hipòtesi del treball fou que la incorporació de WB en la dieta podia estimular el trànsit intestinal i reduir la paràlisis de la digesta intestinal dels garrins, causada per l'anorèxia que pateixen els animals en el període post-deslletament. En aquest experiment, el WB fou comparat amb un fàrmac que s'utilitza en medicina humana per tractar la diarrea que al mateix temps redueix el trànsit intestinal (loperamida). Els resultats de nou mostraren els efectes del WB sobre les característiques físico-químiques de la digesta (increment de la WRC) i la promoció de la fermentació intestinal (incrementant la concentració d'àcid butíric i disminuint la concentració dels isoàcids en la digesta intestinal). De forma inesperada, la loperamida incrementà el consum d'aliment i el creixement dels animals. Suggerírem que aquest efecte estava relacionat amb l'efecte analgèsic i l'activitat opioide d'aquest fàrmac en el tracte intestinal. No poguérem confirmar si el WB reduí el temps de trànsit intestinal o el possible rol que juga la modificació del temps de trànsit intestinal sobre els canvis de la microbiota intestinal. En l'última prova (Prova 4, Molist et al., 2010b) la intenció era confirmar tots els resultats previs (reducció de la població d'enterobactèries i increment de la concentració d'àcid butíric) en un comparació entre la incorporació de WB amb la inclusió d'òxid de zinc (ZnO) en la dieta. El ZnO és un ingredient àmpliament utilitzat en les dietes post-deslletament pel seu efecte antimicrobià similar al que s'obtenia amb la incorporació d'antibiòtics promotors de creixement (AGP) en el pinso, i per tant oposat a l'efecte promogut per la incorporació de fibra en la dieta. A més a més, considerant els resultats observats sobre la reducció de l'adhesió del E. coli K88 a la mucosa ileal promogut per l'addició de WB, es volia clarificar si el WB també podia exercir un efecte físic i blocar l'adhesió del E. coli K88 a la mucosa. Els resultats foren una mica sorprenents perquè s'observà una interacció negativa entre el WB i el ZnO sobre la microbiota intestinal. Aquesta interacció negativa s'associà a la presència de fitats en la dieta. Aquests resultats posaren de relleu la recomanació d'incorporar enzims (fitases) en les dietes després del deslletament amb l'objectiu d'incrementar la biodisponibilitat del zinc de la dieta. També detectarem una alta habilitat de la fracció soluble extreta del WB d'unir-se al E. coli K88 in-vitro. Aquest resultat ens permet suggerir que part dels efectes positius sobre la microbiota intestinal observats amb la incorporació de WB en la dieta eren deguts entre altres factors, a la seva capacitat de blocar l'adhesió de E. coli patògens a la mucosa intestinal. Els resultats exposats en la present tesis, avalen l'estratègia d'incloure un nivell moderat de fibra (>60 g FND/kg per porcs entre 6 - 12 kg) en les dietes post-deslletament. Els resultats obtinguts mostren els efectes positius derivats de la inclusió d'una font de fibra insoluble, com WB, en la modificació de l'ambient intestinal i la instauració d'una microbiota saludable. Aquests efectes beneficiosos observats amb l'addicció de WB s'associaren a modificacions en les característiques físico-químiques de la digesta (increment de la WRC de la digesta) i amb la seva habilitat per blocar l'adhesió del E. coli a la mucosa ileal. Tot i així, el contingut en fitats d'aquest ingredient pot reduir la biodisponibilitat i l'eficàcia del ZnO en la dieta, fins i tot quan es subministra a dosis terapèutiques. És per aquest motiu que proposem considerar l'addició de fitases en dietes post-deslletament a base de cereals per: 1.- incrementar la biodisponibilitat de Zn, 2.- mantenir els efectes beneficiosos relacionat amb la inclusió de ZnO o WB en la dieta, o 3.- reduir la dosis de ZnO en la dieta. / The objective of this thesis was to study whether the incorporation of fibrous ingredients in the diet of piglets would minimize the intestinal disorders that usually occur during the early period after weaning and facilitate the adaptation of the digestive system of the animals in the subsequent growing periods. To achieve this goal, four trials (chapters 4 to 7) were designed. In Trial 1 (Molist et al., 2009a), we first wanted to confirm some preliminary positive results associated with a higher growth rate of the animals obtained when an insoluble fibre source (wheat bran, WB) was introduced in post-weaning diets. At the same time, we wanted to assess whether this type of fibre source was appropiate for this period, or whether it would be more advantageous to incorporate a soluble fibre source (such as the sugar beet pulp, SBP). The study aimed to explore the effects of including two fibre sources (WB, insoluble and SBP, soluble) on the performance, the physicochemical properties of digesta and the metabolic activity and composition of the intestinal microbiota. Results showed that intestinal fermentation was low during the first week after weaning. The addition of WB or WB plus SBP in the diet increased intestinal fermentation and the concentration of butyric acid in the caecum digesta, and reduced the enterobacteria population in faeces. It was concluded that consumption of an insoluble fibre source during the first days after weaning (either WB or WB-SBP) modifies the physicochemical properties of digesta and affects the microbial colonization in the hindgut. We also speculated that the effects observed with the inclusion of WB could be associated with: 1.- changes in the physicochemical properties of digesta, such as the higher water retention capacity (WRC) and fermentation promoted in digesta, 2.- a physical effect related to its larger particle size or 3.- a reduction in the transit time of digesta. In Trial 2 (Molist et al., 2009b), we wanted to confirm the referred reduction of the enterobacteria population promoted by WB, and its likely ability to reduce digestive disturbances after an experimental infection with E. coli K88. In addition, we wanted to clarify whether this effect of WB was related to its particle size. The results confirmed that WB inclusion reduced the E. coli population in the ileum digesta and, more interesting, also reduced the E. coli K88 attachment to the ileum mucosa. Coarse particle size reduced the microbial diversity compared to finely milled WB. The third trial (Trial 3, Molist et al., 2010a) was designed to elucidate whether the positive effects of WB on the intestinal microbiota could be due to an effect of WB on the intestinal transit of the animals. Our hypothesis was that incorporation of WB in the diet could stimulate the intestinal transit and so reduce the intestinal stasis of digesta in the piglets provoked by post-weaning anorexia. In this experiment, WB was compared with a drug used in human medicine to treat diarrhoea that slows the intestinal transit (loperamide). The results again showed the effects of WB on the physicochemical properties of digesta (increasing WRC) and the enhancement of gut fermentation (increasing butyric acid and lowering isoacid concentration associated to gut fermentation). Unexpectedly, loperamide increased the feed intake and animal growth. We suggested that this effect could be associated to its analgesic effect on and opioid activity in the intestinal tract. We were not able to confirm if WB reduced the intestinal transit time or the likely role of the modification of the intestinal transit time in the changes in intestinal microbiota. The last trial (Trial 4, Molist et al., 2010b) intended to confirm all the previous results (the reduction of enterobacteria population and increasing the butyrate concentration) in a comparison between the incorporation of WB with the inclusion of zinc oxide (ZnO) in the diet. ZnO is a widely used ingredient in post-weaning diets producing antimicrobial effects resembling those of the antibiotic growth promoters (AGP) and therefore opposed to the inclusion of fibre in the diet. In addition, and considering the previous observed effects on the E. coli K88 adhesion to the ileum mucosa, we wanted to clarify whether WB could have a physical role on the blockage of the adhesion of E. coli K88 to the mucosa. The results were quite surprising because a negative interaction between WB and ZnO was observed on the intestinal microbiota, which was associated to the presence of phytates in the diet. These results highlighted the recommendation of incorporating enzymes (phytases) in the post-weaning diets in order to increase the bioavailability of zinc. We also detected a high ability of soluble WB extract to bind E. coli K88 in-vitro, which suggests that part of the positive effects on the intestinal microbiota reported with the WB inclusion were due to its ability to block the adhesion of pathogenic E. coli to the intestinal mucosa. Results exposed in this thesis, support the strategy of including a moderate amount of fibre (>60 g NDF/kg for pigs between 6 - 12 kg) in the diets of early weaned pigs. Our results show the positive effects of including an insoluble source, such as WB on the modification of the intestinal environment and the instauration of a healthy microbiota. These beneficial effects of WB inclusion were associated to changes on the physicochemical properties of digesta (like an increasing WRC of the digesta) and with its ability to block E. coli attachment to the ileum mucosa. However, the presence of phytates in this ingredient may also reduce the availability and efficacy of ZnO in the diet, even when it is provided at therapeutic doses. We propose the consideration of the inclusion of phytase in the post-weaning cereal based diets in order to: 1.- increase Zn biovailability, 2.- maintain the beneficial effects related to ZnO or WB inclusion, or 3.- reduce the therapeutic doses of ZnO in the diet.

Durant aquesta tesis es varen realitzar sis estudis en vedells joves amb l’objectiu de conèixer estratègies per incrementar el consum de concentrat al voltant del deslletament. En primer lloc, es realitzà un estudi per desenvolupar un mètode per determinar preferències oro-sensorials en vedells deslletats, aquest mètode va consistir en registrar el consum d’un grup mínim de 20 animals individualitzats, als quals se’ls ofertà una doble opció de dos ingredients o concentrats durant un període de 6 h. Amb aquest mètode es realitzà el segon estudi, on es van determinar les preferències oro-sensorials entre 8 ingredients energètics (arròs, blat, blat de moro, corn gluten feed, civada, melca, ordi i segones de blat) i 6 ingredients proteics (colza, DDG de blat, corn gluten meal, girasol, pèsol i soja). El blat i la soja van ser els ingredients preferits, mentre que el corn gluten feed, l’arròs i el corn gluten meal van ser els ingredients menys preferits a curt termini. En el tercer estudi, es testà l’efecte d’addicionar un edulcorant amb aroma al lactoremplaçant i al concentrat. Al addicionar l’aroma s’observà un increment en el consum de concentrat en aquells vedells que presenten un baix consum al moment del deslletament. El quart estudi avaluà la capacitat de regulació dels requeriments nutricionals en vedells nounats. En aquest estudi un grup de vedells van rebre un concentrat convencional i es van comparar amb un altre grup als quals se’ls ofertà una bateria de diferents ingredients que composaven el concentrat. Els vedells que tenien accés a la bateria d’ingredients van descriure un consum total i creixement similar als vedells que rebien concentrat. Però en canvi van descriure un major consum de proteïna i greix, i un menor consum de carbohidrats. Aquestes diferències es van deure principalment a la predilecció cap a la soja i la soja grassa que van mostrar els animals que podien escollir entre diversos ingredients. El cinquè estudi va analitzar el paper de la mida de partícula del farratge en vedells lactants. En aquest estudi es comparaven dos tipus de dietes, composades per un concentrat convencional al qual se li addicionava un 10% de farratge. Aquestes dues dietes diferien en la mida de partícula del farratge, molturat (2mm) o trinxat (3-4cm). Es va observar que els animals que rebien el farratge més groller (3-4 cm) incrementaven més el seu consum la setmana desprès del deslletament, millorava la seva digestibilitat de matèria seca, proteïna, fibra neutra detergent i àcid detergent, i també reduïa la realització de conductes orals no-nutritives. Es va realitzar un sisè estudi on es va avaluar el paper que tenen els opioids en la regulació de la ingesta mitjançant l’estimulació o inhibició del plaer. En aquest estudi es va provar l’efecte de la naloxona, un antagonista opioide, sobre l’elecció de concentrats preferibles en vedells deslletats, i les seves possibles interaccions amb altres metabòlits relacionats amb la regulació de la ingesta. Es va observar que en animals saciats la naloxona podria reduir el consum, indicant que els opioids intervenen en la regulació de la ingesta total, però a més es va observar redueix la preferència per concentrats amb edulcorants, que prèviament s’havien observat altament preferibles. Pel que fa als metabòlits analitzats només es va observar una interacció entre la naloxona i els nivells de glucagon-like peptide-1. Resumint, els vedells lactants van mostrar preferència pels edulcorants al voltant del deslletament, tant a curt termini com a llarg termini. La soja va ser un ingredient d’elecció, mentre que la civada no va ser desitjada, tant a curt termini com a llarg termini. El fet d’addicionar un mateix aroma amb edulcorant al concentrat com a la llet va incrementar el consum d’aquells animals que presentaven un consum baix prèviament al deslletament. La mida de partícula del farratge va condicionar el creixement, consum, digestibilitat i comportament dels vedells al voltant del deslletament. Finalment, es va observar que els opioides juguen un paper important en la regulació de la ingesta mitjançant l’hedonisme o el plaer. / In this thesis, six studies in young calves were performed in order to find strategies to increase concentrate intake around weaning. The first study was conducted to develop a method to determine oro-sensory preferences in weaned calves. This method consist on measure the solid feed consumption of a minimum group of 20 calves, which recieve two options of concentrates or ingredients during a period of 6 h. Using this method, the second study was performed, where the oro-sensory preferences between 8 energetic ingredients (rice, wheat, corn, corn gluten feed, oats, sorghum, barley and second wheat) and 6 protein ingredients (canola, corn DDG, corn gluten meal, sunflower, soybean and pea) were determined. Wheat and soybean meal were the favorite ingredients for weaned calves, while the corn gluten feed, rice and corn gluten meal ingredients were less preferred in this short term study. The third study was conducted to evaluate the effect of flavoring a starter concentrate in a same manner as a milk replacer on intake and performance of young calves. This study claims, that offering a starter concentrate flavored as the milk replacer enhances solid feed consumption of those calves that have a low intake around weaning. The fourth study evaluated the ability of calves to meet their nutrient requirements when different ingredients were offered indepently in newborn calves. In this study a group of calves received a conventional concentrate whereas another group received a battery of different ingredients. The calves that had access to the free-choice of ingredients described a similar total consumption and growth compared to calves that received concentrate. However, calves that had access to all ingredients described a higher consumption of protein and fat, and lower consumption of carbohydrates that those receiving concentrate. These differences in nutrient intake were mainly due to the preference toward soybean meal and soybean full fat described by the animals that had access to all ingredients. The fifth study analyzed the role of particle size of forage in lactating cattle. This study compared two diets, composed of a conventional concentrate with a 10% of forage added. These two diets were different in the particle size of forage, ground (2 mm) or choped (3-4cm). It was observed that animals receiving chopped forage (3-4 cm) increased solid feed consumption the week after weaning, improved the apparent digestibility of dry matter, crude protein, neutral detergent fibre and acid detergent fibre, and reduce undesired behaviors, such as non-nutritive oral behaviors. The sixth study was conducted to evaluate the role of opioids in the regulation of food intake by stimulation or inhibition of pleasure. This study tested the effect of naloxone, an opioid antagonist, on preferred concentrates consumption in weaned calves, and their possible interactions with other metabolites related to the regulation of food intake. It was observed that satiated animals treated with naloxone reduced solid feed consumption, indicating that opioids are involved in the regulation of total intake. Furthermore, calves treated with naloxone reduced their preference for concentrate with sweetener, which had been previously observed as a preferred concentrate. Regarding the analyzed metabolites, GLP-1 was influences by naloxone administration. In summary, calves showed preference for sweeteners around weaning, either in short term or long term assays. Soybean meal was a preferred ingredient, while oats was not desired, both in short term and long term. Adding a sweetener with the same aroma in concentrate and in milk replacer increased consumption of animals that had a low intake prior to weaning. The particle size of forage influenced the growth, consumption, digestibility and performance of calves around weaning. Finally, we observed that opioids play an important role in the regulation of food intake by hedonism or pleasure.