Yes they can. However a horse cannot utilize urea like ruminants as urea is quickly absorbed from the small intestine and excreted before reaching the hindgut (where non-protein nitrogen would be converted to useful protein).

Horses are less likely to suffer from urea toxicity than ruminants tolerating up to 500grams of urea in their daily diet. However a single dose of 500 grams or more of urea is known to cause severe illness.

Hence, horses can tolerate cattle feeds such as drylicks and molasses which contain urea.