amin ating ▁their ▁gene ▁pool . ▁The ▁two ▁notable ▁cent res ▁for ▁experiments ▁on ▁the ▁species ▁were ▁Ł ę k no ▁( 3 9 1 ▁animals ▁altogether ) ▁and ▁Pop iel no ▁( 1 2 1 ▁animals ), ▁while ▁limited ▁experiments ▁were ▁also ▁held ▁in ▁the ▁reserve ▁of ▁Ask ania ▁Nova ▁in ▁the ▁USS R . ▁This ▁was ▁dis cont in ued , ▁and ▁the ▁sole ▁surv iving ▁her d ▁consists ▁of ▁several ▁animals ▁only , ▁kept ▁at ▁B ial ow ies ki ▁National ▁Park . ▁As ▁of ▁ 2 0 0 7 , ▁however , ▁there ▁are ▁press ▁releases ▁suggesting ▁the ▁bre eding ▁and ▁experiments ▁are ▁continu ing ▁in ▁Kar ole w ▁in ▁Gre ater ▁Poland . ▁ ▁Description ▁Ż ub ro ń ▁are ▁heavy ▁animals , ▁with ▁males ▁we igh ing ▁up ▁to ▁ ▁and ▁females ▁up ▁to ▁. ▁They ▁are ▁strong , ▁resist ant ▁to ▁disease , ▁and ▁toler ant ▁of ▁har sh ▁weather ▁conditions . ▁The ▁first - cross ▁cal ves ▁have ▁to ▁be ▁born ▁by ▁Ca es are an ▁section , ▁because ▁although ▁they ▁may ▁be ▁carried ▁successfully ▁to ▁full ▁term , ▁part ur ition ▁never ▁occurs . ▁M ales ▁are ▁infer t ile ▁in ▁the ▁first ▁generation . ▁ ▁Fem ales ▁are ▁fert ile ▁and ▁can ▁be ▁cross bre d ▁with ▁either ▁parent ▁species , ▁i . e . ▁with ▁cattle ▁or ▁wis ent , ▁and ▁males ▁from ▁these ▁back cross es ▁are ▁fert ile . ▁ ▁See ▁also ▁ ▁Be ef alo ▁ ▁D zo ▁