underfeed

The animal was so underfed that his ribs were showing under his lusterless chestnut coat.

The animals are mostly worked far too early, and underfed, and the majority are consequently undersized and of poor quality.

The children who crowd these grimy alleys, half-clad and underfed, shrink away from your outstretched hand as if from a blow.

I ain't sure of the word, but I believe that means thin-blooded or underfed.