"Are you looking for big pigs, big sheep, or big horses?"
Translation:Hledáte velká prasata, velké ovce nebo velké koně?
Velkého is the singular (masculine animate) form in the accusative, while the nouns here are plural. Ovce is feminine and prasata is neuter, and they take velké and velká, respectively. Velké is correct for masculine animate nouns in the accusative plural. You can see the full declension table here: https://en.wiktionary.org/wiki/velk%C3%BD.