This comes from Morgunblaðið:
Félag tamningamanna mælir með tamningaraðferðum sem byggja á gagnkvæmri virðingu og trausti milli manns og hests (The horse trainers society advises training methods that are built upon mutual respect and trust between man and horse.)
"hestur" is in indefinite genitive case here because of the preposition "milli"