o ▁transfer , ▁or ▁both . ▁The ▁high ▁value ▁of ▁st all ions ▁has ▁helped ▁with ▁the ▁accept ance ▁of ▁these ▁techniques ▁because ▁they ▁allow ▁a ▁st all ion ▁to ▁bre ed ▁more ▁mar es ▁with ▁each ▁" collection " ▁and ▁greatly ▁reduce ▁the ▁risk ▁of ▁injury ▁during ▁m ating . ▁Cl oning ▁of ▁horses ▁is ▁highly ▁controvers ial , ▁and ▁at ▁the ▁present ▁time ▁most ▁main stream ▁bre ed ▁reg ist ries ▁will ▁not ▁accept ▁cl oned ▁horses , ▁though ▁several ▁cl oned ▁horses ▁and ▁m ules ▁have ▁been ▁produced . ▁Such ▁restrictions ▁have ▁led ▁to ▁legal ▁challeng es ▁in ▁the ▁United ▁States , ▁som etime ▁based ▁on ▁state ▁law ▁and ▁sometimes ▁based ▁on ▁ant it rust ▁laws . ▁ ▁Hy br ids ▁H ors es ▁can ▁cross bre ed ▁with ▁other ▁equ ine ▁species ▁to ▁produce ▁hy br ids . ▁These ▁hy brid ▁types ▁are ▁not ▁bre eds , ▁but ▁they ▁res emble ▁bre eds ▁in ▁that ▁cross es ▁between ▁certain ▁horse ▁bre eds ▁and ▁other ▁equ ine ▁species ▁produce ▁characteristic ▁off spring . ▁ ▁The ▁most ▁common ▁hy brid ▁is ▁the ▁m ule , ▁a ▁cross ▁between ▁a ▁" jack " ▁( male ▁don key ) ▁and ▁a ▁mare . ▁A ▁related ▁hy brid , ▁the ▁hin ny , ▁is ▁a ▁cross ▁between ▁a ▁st all ion ▁and ▁a ▁j en ny ▁( f em ale ▁don key ). ▁Most ▁other ▁hy br ids ▁involve ▁the ▁z eb ra ▁( see ▁Z eb roid ). ▁ ▁With ▁rare ▁exceptions ,