The most common and most likely answer to this crossword clue is the 4 letter word HOSS
H
O
S
S
Buddy explains!
The straight part
We know that "Colt maybe/wh/at no cowboy could do without" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case colt maybe/wh/at no cowboy could do without = hoss.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does HOSS mean?
HOSS noun- Any of several animals related to Equus ferus caballus.
- Equipment with legs.
- Type of equipment.
- A mass of earthy matter, or rock of the same character as the wall rock, occurring in the course of a vein, as of coal or ore; hence, to take horse (said of a vein) is to divide into branches for a distance.
- The sedative, antidepressant, and anxiolytic drug morphine, chiefly when used illicitly.
- An informal variant of basketball in which players match shots made by their opponent(s), each miss adding a letter to the word "horse", with 5 misses spelling the whole word and eliminating a player, until only the winner is left. Also HORSE, H-O-R-S-E or H.O.R.S.E. (see Variations of basketball#H-O-R-S-E).
- (among students) A translation or other illegitimate aid in study or examination.
- (among students) horseplay; tomfoolery
- Heroin (drug).
- A big, strong and respected or dependable person, usually a man; one who is large like a horse.
- (often capitalized) Term of address for a man.
- A car.