1. A method for the treatment and/or prevention of gastrointestinal disease and/or infection and/or diarrhoea in humans, animals or birds resulting from the microbial infection of the gastrointestinal tract in said humans, animals or birds, comprising oral administering to said humans, animals or birds an antimicrobially effective amount of a antimicrobial composition, comprising a polymer or copolymer with a molecular mass of at least 1000, having the repeating polymeric unit:  wherein R is H or C1-C4alkyl, or this unit in hydrated, hemiacetal or acetal form, at that the polymer or copolymer comprises carboxyl groups in the amount of 0.1 to 5 mole per 1 kg of a polymer or copolymer by weight. 2. The method according to any one of Claims 1 or 2, characterized in that the polymer or copolymer comprises one or more repeating units, selected from the group which structures are represented with the following formulae:     or     wherein n >=1 and R - H or C1-C4alkyl. 3. The method according to any one of Claims 1 or 2, characterized in that the infection is a microbial infection. 4. The method according to any one of Claims 1 to 3, characterized in that the infection is a colibacillosis and/or is associated with the proliferation of Escherichia coli bacteria. 5. The method according to any one of Claims 1 to 3, characterized in that the infection is associated with the proliferation of Helicobactor pylori bacteria. 6. The method according to any one of Claims 1 to 3, characterized in that the infection is associated with the proliferation of Staphylococcus aureus bacteria. 7. The method according to any one of Claims 1 to 6, characterized in that the antimicrobial composition is administered to dogs, pigs, sheep, horses, cattle or cats. 8. The method according to Claim 7, characterized in that the antimicrobial composition is administered to pigs. 9. The method according to any of Claims 1 to 6, characterized in that the antimicrobial composition is administered to poultry, ducks, turkeys, quail or pheasants. 10. The method according to any of Claims 1 to 9, characterized in that the antimicrobial composition is wholly or partly contained within a controlled-delivery system. 11. The method according to Claim 10, wherein said controlled-delivery system is pH sensitive. 12. The method according to any of Claims 10 to 11, characterized in that the controlled-delivery system is based upon insoluble, cross-linked polymers and/or copolymers of acrylic acid, or polymers and/or copolymers of acrylic acid and acrylamide. 13. The method according to any one of Claims 10 to 12, wherein the controlled-delivery system is cross-linked and/or absorbent and when wet is a gel. 14. The method according to any one of Claims 10 to 13, wherein the controlled-delivery system is pre-heat for sterilisation thereof. 15. An antibacterial composition for oral administration to humans, animals or birds suffering from gastrointestinal disease and/or infection and/or diarrhoea, resulting from the infection of the gastrointestinal tract, comprising an antimicrobial composition, comprising a polymer or copolymer with a molecular mass of at least 1000, having the repeating polymeric unit:  wherein R is H or C1-C4alkyl, or this unit in hydrated, hemiacetal or acetal form, at that the polymer or copolymer comprises carboxyl groups in the amount of 0.1 to 5 mole per 1 kg of a polymer or copolymer by weight and a pharmaceutically or veterinarally acceptable carrier, appropriate for oral administration. 16. A composition according to Claim 15, wherein the carrier comprises the controlled-delivery system. 17. A composition according to Claim 16, wherein the controlled-delivery system comprises an external polymeric matrix from insoluble cross-linked absorbing polymer, having ion groups. 18. A composition according to Claim 17, wherein the absorbing polymer of the external polymeric matrix is acrylic acid and/or copolymers of acrylic acid and acrylamide. 19. A method for obtaining a composition according to one of Claims 17 or 18, wherein the external polymeric matrix is added to a solution and/or suspension and/or emulsion of the antimicrobial composition. 20. A method according to Claim 18, wherein while the polymeric matrix is added to a solution and/or suspension and/or emulsion of the antimicrobial composition the antimicrobial composition is dissolved in aqueous solution of alkali or a base, the obtained solution is neutralized with acid; insoluble, cross-linked absorbing polymers of acrylic acid and/or copolymers of acrylic acid and acrylamide with forming of swollen granules are added to the neutralized solution. 21. A method according to one of Claims 19 or 20, wherein further the composition is dried, at least partly or fully. 22. A food for humans, or feed for animals or birds, characterized in that it comprises a composition according to any one of Claims 17 to 18.