free ▁range " ▁to ▁include ▁" h erd ing ", ▁free ▁range ▁was ▁a ▁typical ▁husband ry ▁method ▁at ▁least ▁until ▁the ▁development ▁of ▁bar bed ▁wire ▁and ▁ch icken ▁wire . ▁The ▁generally ▁poor ▁understanding ▁of ▁nut r ition ▁and ▁dise ases ▁before ▁the ▁tw enti eth ▁century ▁made ▁it ▁difficult ▁to ▁raise ▁many ▁liv est ock ▁species ▁without ▁giving ▁them ▁access ▁to ▁a ▁varied ▁di et , ▁and ▁the ▁labor ▁of ▁keeping ▁liv est ock ▁in ▁conf in ement ▁and ▁carrying ▁all ▁their ▁feed ▁to ▁them ▁was ▁prohib itive ▁except ▁for ▁high - pro fit ▁animals ▁such ▁as ▁da iry ▁cattle . ▁ ▁In ▁the ▁case ▁of ▁p oul try , ▁free ▁range ▁was ▁the ▁dominant ▁system ▁until ▁the ▁discovery ▁of ▁vit am ins ▁A ▁and ▁D ▁in ▁the ▁ 1 9 2 0 s , ▁which ▁allowed ▁conf in ement ▁to ▁be ▁pract ised ▁successfully ▁on ▁a ▁commercial ▁scale . ▁Before ▁that , ▁green ▁feed ▁and ▁sun sh ine ▁( for ▁the ▁vit amin ▁D ) ▁were ▁necessary ▁to ▁provide ▁the ▁necessary ▁vit amin ▁content . ▁Some ▁large ▁commercial ▁bre eding ▁f lock s ▁were ▁re ared ▁on ▁past ure ▁into ▁the ▁ 1 9 5 0 s . ▁N ut r itional ▁science ▁resulted ▁in ▁the ▁increased ▁use ▁of ▁conf in ement ▁for ▁other ▁liv est ock ▁species ▁in ▁much ▁the ▁same ▁way . ▁ ▁United ▁States ▁In ▁the ▁United ▁States , ▁the ▁US DA ▁free ▁range ▁reg ulations ▁currently ▁apply ▁only ▁to ▁p oul try ▁and ▁indicate ▁that