**2. Materials and methods**

376 New Advances in the Basic and Clinical Gastroenterology

important to young growing pigs so they may attain maximum digestive and absorptive capability. Consequently, suboptimal or adverse environmental factors, influencing the morphological development of intestinal tissue, may have critical functional consequences for the young growing pig. The marked and abrupt morphological responses to weaning in the small intestine, characterized by the transformation from a dense finger-like villi population to a smooth, compact, tongue-shaped luminal villi surface may indicate critical consequences for the young pig digestive capacity and subsequent use of nutrients during the starter phase (Skrzypek et al., 2005). The changes at weaning which include shortening of villi, hyperplasia of crypts, decrease in absorption capacity and certain loss of carbohydrate activity may, in combination with changes in the number and type of enterobacteria, induce various degree of post-weaning diarrhoea (Pluske et al., 1997). By now, the prevention and therapy of diseases of sucklings and weanlings was implemented by means of synthetic substances, which enormously burden not only the organisms, but also the living environment as a whole. The extensive use of antibiotics has increased the risk of development of resistance in human and animal pathogens and chemical residues in meat of animals. In progress is the research and development of new methods of biotechnological and natural character that with their complex influence will maximally make efficient the prevention of diseases of animals by the stabilisation of physiological function of biological barriers of the gastrointestinal tract ecosystem. Biological barriers of digestive tract represent the prime and basal protection of organism from negative impacts of external and internal environment, and therefore it is possible to decrease a health risk by its sophisticated modulation. The indigenous microbiota suppresses colonization of incoming bacteria by a process named colonization resistance that is a first line of defence against invasion by exogenous, potential pathogenic organisms or indigenous opportunists. Beneficial microbiota prevent bacterial colonization by competing for epithelium receptors and enteric nutrients, producing antimicrobial compounds such as bacteriocins and metabolizing nutrients to create a restrictive environment which is generally unfavourable for the growth of many enteric pathogens (Bomba et al., 2002; Marinho et al., 2007). Probiotics as natural bioregulators assist the maintenance of the homeostasis of the gastrointestinal tract ecosystem and, during the critical periods of animal life, can play an important role in prevention of diarrhoeic diseases of dietetic and bacterial origin (Bomba et al., 2002; Marinho et al., 2007). Gastrointestinal microflora may be affected by adding probiotic micro-organisms of genera *Lactobacillus*, *Bifidobacterium* (Bomba et al., 2002), *Bacillus*, *Enterococcus* and *Streptococcus* (Scharek et al., 2005) to feed or by their combinations (Bomba et al., 2002; Mathew et al., 1998). Enterococci belong to those lactic-acid bacteria which inhabit human and animal intestines (Devriese et al., 1991). It was observed that *Enterococcus faecium* prevents adherence of enterotoxigenic *Escherichia coli* K 88+ to the surface of intestinal mucosa of piglets (Scharek et al., 2005). In terms of exactitude and interpretability of results, gnotobiotic piglets are an ideal experimental model for the study of digestive processes and their development. The presence of normal microflora influences the structure of the host intestinal mucous membrane, its function and short-chain fatty acids (SCFAs) production. By means of gnotobiotic conditions, we excluded the influence of the normal microflora and sow's milk. The changes in the small intestine, observed under the specific controlled conditions,

were compared to the development of the gut in conventionally bred piglets.

The aim of the study was to evaluate the effects of piglet´s age and diet (natural feeding, artificial feeding and gnotobiotic conditions) on the development of microflora, production of short-chain fatty acids (SCFAs), postnatal morphological development and The experiments on growing and weaned piglets were carried out at the Institute of Microbiology and Gnotobiology, University of Veterinary Medicine and Pharmacy, Košice, Slovakia. The State Veterinary and Food Administration of the Slovak Republic approved the experimental protocols and the animals were handled and sacrificed in a humane manner in accordance with the guidelines established by the relevant commission.
