prize-winning heifer

prize-winning + heifer

The phrase is fully compositional: 'prize-winning' straightforwardly means 'having won a prize' (derivable from 'prize' + 'win/ning') and 'heifer' is a young female cow, so the combined meaning is a young female cow that has won a prize. This modifier+noun pattern is common and cross-linguistically transparent, so a B1 learner who knows the constituents would readily infer the meaning.

Prize-winning heifer comes from county fairs where a heifer, a young female cow, is washed, brushed and led into a ring so judges can give a prize. So the phrase means a young female cow that has 'won a prize' for being especially good.