The present PhD Thesis aims to simulate different physiological or nutritional status that post-weaned piglets face in the intensive production system, e.g., variations in the dietary nutritional content, in the availability of nutrients or feeds, or in the animals’ homeostasis. It is hypothesized that commercial piglets may have retained the capacity to perform appropriate dietary selection patterns in relation to their needs, even when the common feeding practices in the pig industry do not allow animals to select their own diet composition. Chapter 1 assesses whether dietary energy density affects the preference of piglets for protein or carbohydrate sources. One experiment was conducted by using two isoproteic pre-starter diets differing in the digestible energy content, a high-energy (HE) and a low-energy (LE) diet. The LE diet promoted a higher performance than did the HE diet after 14 or 21 days of feeding. Preference was not observed for protein or carbohydrate solutions in piglets fed the LE diet. On the other hand, piglets fed the HE diet showed a higher preference for sucrose solution. Chapter 2 evaluates whether piglets submitted to a protein-deficiency status are able to select and prefer protein sources to overcome the deficiency. Two isoenergetic pre-starter diets differing in the crude protein content were used in two experiments, a high-protein (HP) and a low-protein (LP) diet. In Experiment 1, piglets showed higher intake and preference for sucrose than for a protein solution, independently of the dietary crude protein content. In Experiment 2, piglets were given eight conditioning sessions with two equally preferred flavors mixed into protein (CSp) or carbohydrate (CSc) solutions. Subsequently, piglets fed the LP diet showed a higher intake and preference for CSp than for CSc, differences being higher for medium and low weight piglets. Chapter 3 studies whether a long-term exposure to carbohydrate and artificial sweetener solutions has an effect on feeding behavior of piglets. Animals were offered in three different experiments a long-term availability to sucrose 160 g/L, maltodextrin 160 g/L, and saccharin 0.08 g/L plus neohesperidin dihydrochalcone (NHDC) 0.02 g/L solutions as supplement to the maintenance diet. In Experiment 1, piglets showed a higher intake of sucrose 160 g/L than of water and a decrease in feed intake and weight gain. A similar situation occurred in the last days of maltodextrin 160 g/L exposure in Experiment 2. In contrast, animals were not influenced by saccharin 0.08 g/L plus NHDC 0.02 g/L in Experiment 3. After solutions exposure, a reduction in sucrose 20 g/L preference and appetence was observed in Experiments 1 and 2, but not Experiment 3. Chapter 4 estimates whether dietary electrolyte balance (dEB) influences feed preference, appetence and growth performance of piglets. Seven isoproteic and isoenergetic starter diets differing in the dEB were used in three distinct experiments, diets ranging from -16 mEq/kg to 388 mEq/kg. Productive results of Experiments 1 and 2 showed that low rather than high dEB levels optimized growth performance of piglets. In Experiments 2 and 3 piglets had the opportunity to choose between these diets, being unable to select the diet that optimized their performance neither in short- nor long-term preference tests, showing also a higher appetence for high dEB levels. It is concluded that piglets might be able to perform appropriate dietary selection patterns in relation to different nutritional status, but critically whether a learning process has been carried out. In the absence of learning, such as in the intensive pig industry conditions at weaning, piglets might be unable to overcome a particular situation that departs from an optimal state just relying on their innate dietary preferences and aversions.