Hay Quality refers to the hay’s nutritional value, it’s acceptability by your horse, and the type and amount of foreign material it contains. Good quality hay is readily consumed, is highly digestible, high in nutrients and devoid of foreign material.

Characteristics of quality hay are:

1) free of mold, dust, weeds, & foreign material.

2) leafy with fine stems

3) soft & pliable to the touch

4) fragrant aroma

5) bright green as opposed to brown, or  yellow although this may be the least important factor

Generally, if it is soft loose hay that lacks course stems, or stalks and weeds,  is nice and clean with a fresh smell little or no dust or other foreign material and you would sleep in it, then it most likely is of good quality.

Source: Feeding and Care of the Horse (second edition)