Slg preparation comprising SIgA and/or SIgM and a Vitamin A supplement, for use in the therapy or prophylaxis of mucosal immunoglobulin deficiency, as well as an oral immunoglobulin preparation comprising—a single-dose of 10 mg to 10 g SIgA and/or SIgM, and—a single-dose of 100 to 5000 micrograms retinol activity equivalents (RAE) Vitamin A, preferably retinylpalmitate, and optionally further components selected from the group consisting of vitamins and minerals.