The invention relates to a method comprising the step of incubating chitosan in an aqueous solution of an organic carboxylic acid or a salt thereof, a modified chitosan obtainable by the method of the present invention, a hydro colloid, a compound of formula [X]n, a composition comprising the modified chitosan, the hydro colloid or compound according to the present invention, the modified chitosan, the hydro colloid, the compound or composition according to the present invention for use in human and/or veterinary medicine and the modified chitosan, the hydro colloid, the compound or composition according to the present invention for use in a method of treating and/or preventing mastitis, preferably latent mastitis and/or acute mastitis, endometritis, preferably chronic, acute and/or purulent-catarrhal endometritis, hoof- and claw diseases, lameness, lesions in the interdigital space, digital dermatitis, interdigital dermatitis, interdigital phlegmon, trichophytosis, microsporosis, mycosis of skin, allergies, as well as diseases complicated by allergies, in particular allergic obstructive pulmonary disease, allergic skin diseases, allergic ear erythema, allergic rhinitis, allergic conjunctivitis, acute allergic contact dermatitis, chronic allergic contact eczema or atopic eczema, obstructive pulmonary disease, in particular chronic obstructive pulmonary disease, skin diseases, in particular dermatitis, ear erythema, rhinitis, conjunctivitis, dermatophytosis or warts, in particular Common warts, in a subject and for modulating the immune response in a subject and/or for enhancing reproduction efficiency, preferably reproduction efficiency in animal breeding.
