▁reported ▁that ▁there ▁was ▁usually ▁clear ▁evidence ▁of ▁t issue ▁damage ▁in ▁the ▁es oph ag us ▁of ▁birds ▁which ▁had ▁been ▁g av age ▁fed , ▁although ▁one ▁ 1 9 7 2 ▁study ▁c ited ▁by ▁the ▁report ▁observed ▁no ▁alter ation ▁of ▁the ▁es oph age al ▁t issue . ▁More ▁recent ▁scientific ▁studies ▁have ▁shown ▁that ▁the ▁es oph ag us ▁of ▁birds ▁can ▁be ▁injured ▁or ▁infl amed ▁by ▁g av age ▁feed ing . ▁ ▁Str ess ▁After ▁meas uring ▁a ▁range ▁of ▁phys i ological ▁parameters ▁in ▁male ▁Mul ard ▁du cks , ▁it ▁was ▁concluded ▁in ▁one ▁study ▁that ▁the ▁ac ute ▁stress ▁caused ▁by ▁force ▁feed ing ▁is ▁similar ▁at ▁the ▁beginning ▁and ▁end ▁of ▁the ▁commercial ▁production ▁of ▁fo ie ▁gr as . ▁A ▁similar ▁study ▁on ▁Mus c ovy ▁du cks ▁found ▁that ▁g av age ▁feed ing ▁was ▁related ▁to ▁an ▁increase ▁in ▁p ant ing ▁behaviour ▁and ▁ser um ▁cort ic oster one ▁levels , ▁indicating ▁increased ▁stress ▁att rib utable ▁to ▁this ▁feed ing ▁method . ▁ ▁H ous ing ▁and ▁husband ry ▁In ▁France , ▁at ▁the ▁end ▁of ▁ 2 0 1 5 , ▁individual ▁c ages ▁were ▁prohib ited ▁to ▁improve ▁animal ▁w elf are . ▁ ▁They ▁will ▁be ▁replaced ▁by ▁c ages ▁which ▁house ▁ 4 ▁to ▁ 5 ▁birds . ▁ ▁Be hav iour al ▁restriction ▁During ▁the ▁force - feed ing ▁period , ▁the ▁birds ▁are ▁kept ▁in ▁individual ▁c ages ,