Hard keeper

A hard keeper or (British English) poor doer is a horse or other livestock animal that is naturally prone to be thin, will lose weight quickly, and has difficulty gaining weight.

A horse that is too thin is not necessarily a hard keeper. The animal may be ill, elderly, or has not been provided adequate nutrition. Whenever a horse is too thin, it is well-advised to have a veterinarian give the horse a thorough examination and recommend the best course of action.

The opposite of a hard keeper is an easy keeper (good doer); an animal that can live on relatively little food and is prone to obesity and other health problems associated with a too-rich diet. In contrast, a truly hard keeper is almost never fat under any circumstances.