Process for increasing the egg production and strengthening the eggshells of poultry

Process for increasing egg production and strengthening eggshells in poultry, which comprises the administration to the poultry animal of at least one bisphosphonic compound selected from the group consisting of:

• a) 4-chlorophenylthiomethylenebisphosphonic acid, a physiologically acceptable salt thereof, hydrates thereof, and mixtures thereof and
• b) compound of formula I:
• in which:
• R1 is a halogen atom or a (C1-C12) alkyl group which is optionally substituted with one or more halogen atoms and
• R2 is a thiol substituted with (C6-C12)aryl or (C4-C10)heteroaryl optionally substituted with one or more thiol and/or halogen groups,
• wherein the at least one bisphosphonic compound is administered at a dose sufficient for inhibiting bone resorption and is administered within two months before the age of onset of laying.