How many letters does the top answer for “urinate, of cattle and horses” have?

The most common answer is stale (5 letters).

Crossword clue: urinate, of cattle and horses

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

stale 5 letters wn-def

lacking freshness, palatability, or showing deterioration from age