0 0 7 ) ▁Ste iss , ▁et ▁al ., ▁conducted ▁a ▁four - week ▁study ▁of ▁adult ▁shelter ▁dogs ’ ▁phys i ological ▁and ▁behavior al ▁responses ▁to ▁b ark ▁control ▁coll ars . ▁Pl asma ▁cort is ol ▁was ▁used ▁as ▁the ▁stress ▁measure . ▁D ogs ▁were ▁randomly ▁assigned ▁to ▁either ▁a ▁shock ▁col lar , ▁a ▁sp ray ▁col lar , ▁or ▁a ▁dummy ▁col lar ▁( control ▁group ). ▁D ogs ▁that ▁were ▁known ▁to ▁b ark ▁at ▁an ▁un famil iar ▁dog ▁were ▁used ▁for ▁the ▁study . ▁Test ▁conditions ▁involved ▁presentation ▁of ▁an ▁un famil iar ▁dog . ▁D ogs ▁wore ▁activ ated ▁coll ars ▁for ▁period ▁of ▁ 3 0 ▁minutes ▁per ▁day ▁for ▁three ▁days ▁in ▁two ▁consecutive ▁weeks . ▁The ▁amount ▁of ▁b ark ing ▁was ▁significantly ▁reduced ▁starting ▁on ▁the ▁second ▁day ▁with ▁both ▁the ▁sp ray ▁and ▁shock ▁coll ars . ▁There ▁was ▁no ▁significant ▁difference ▁in ▁effect ▁between ▁the ▁two ▁col lar ▁types . ▁The ▁treatment ▁group ▁dogs ▁showed ▁a ▁m ild ▁yet ▁statist ically ▁significant ▁increase ▁in ▁blood ▁cort is ol ▁level ▁( an ▁indicator ▁of ▁stress ) ▁only ▁on ▁the ▁first ▁day ▁of ▁we aring ▁the ▁coll ars ▁( as ▁compared ▁to ▁the ▁Control ▁Group .) ▁At ▁the ▁conclusion ▁of ▁the ▁study , ▁Dr . ▁Ste iss ▁and ▁her ▁team ▁concluded ▁that ▁" In ▁the ▁present ▁study , ▁with ▁dogs ▁we aring ▁b ark ▁control ▁coll ars ▁inter mitt ently ▁over ▁a ▁ 2 - week ▁period ,