In Vitro and In Vivo Studies on the Effect of Nucleotides in the Nutrition of Newly Weaned Pigs

Since 2006, there is a general ban of in-feed antibiotics in animal production in the European Union. Thus, it is necessary to focus on alternative products to diminish post-weaning associated diarrhoea in piglets. Nucleotides (NT) are parts ofthe non-protein fraction of mammalian milk. They have been described as possible bioactive agents to alleviate weaning-associated disorders, due to their potential effects on pigs' growth performance, immune response, intestinal microbiota, and gut morphology. Although NT are synthesized endogenously, it has been shown that they may become semi-essential nutrients, especially in times of disease or intensive growth. However, feed ingredients commonly used in pig nutrition (e.g. grains, soy proteins) have been shown to contain only small amounts of NT, when compared with sow's milk. In general, NT can be supplemented to pig diets as live yeast or yeast extracts containing NT, but also in the form of purified NT. However, under practical conditions, diets are usually supplemented with yeast extracts or live yeasts. Thus, currently available literature data are based on studies with pigs in which yeast NT rather than pure NT were added to pigs' diet. The objective of the present thesis was to evaluate, whether dietary NT would be useful to alleviate weaning-associated challenges in piglets. Therefore, firstly biochemical and functional characteristics of NT, their importance as semi-essential compounds in pigs' diet and the variation of individual NT in milk of different species were evaluated, based on current literature data. Additionally, potential physiologieal, morphological, metabolic, immunological, microbial and zootechnical effects of NT in the nutrition of monogastric animals were reviewed. Secondly, based on the information gained from current literature, an in vitro study including two experiments was designed to study the effects of pure NT added to culture media containing several bacterial strains usually harbouring the digestive tract of pigs. Thirdly, two in vivo studies were conducted in which both, yeast NT and pure NT, were supplemented to a diet fed to newly weaned piglets. One study aimed to assess possible short-term effects of yeast NT on ileal nutrient digestibilities, ileal microbial community, ileal microbial metabolites as weil as on ileal enzyme activities. In the other in vivo study, potential effects of a mixture of pure nucleotides on piglets' growth performance, intestinal morphology, immune response and microbial community in different parts of the digestive tract were determined.