MPs have agreed expanding the definition of horse to include ponies is not necessary for proposed new laws on controlling fly grazing, being sponsored by a York MP.

In bizarre exchanges, Tory James Arbuthnot moved an amendment to the Control of Horses Bill which would have added pony and jennet to the included animals covered by the Bill. The original draft included ass, mule or hinny, as well as horses.

But the North East Hampshire MP was assured by his colleagues, including the Bill's sponsor, York Outer MP Julian Sturdy, the amendment was unnecessary

Mr Arbuthnot said: "I just suggest the Bill should, as the Welsh equivalent Bill does, make it clear the word horse includes ponies and jennets."

Liberal Democrat David Heath intervened and said: "I do think the normal definition of a horse would involve anything which was of the same species as a horse, which is to say equus ferus caballus, which ponies and jennets are.

"The reason donkeys are separately identified is because they are not the same species - they are equus africanus asinus if I remember correctly, so they have to defined separately."

Mr Arbuthnot said: "You are almost certainly right. It is quite clear from your intervention that you know far more than I do about these matters - probably most matters."

He added: "If this amendment is unnecessary and we don't need to define what a horse is, as you suggest, then I will move on."

Environment Minister George Eustice endorsed Mr Heath's explanation, leading Mr Arbuthnot to withdraw his amendment.

Mr Eustice added: "For the purposes of the law, a donkey is an ass... a pony is simply a small horse and therefore does not need to be specifically covered."

Mr Sturdy's Bill, which allows councils to seize stray horses in public places, was granted an unopposed third reading. It will be sent to the Lords for further scrutiny.