Unknown plant in my horse field

Found this growing in my horse field in a pile of manure.Just when most summer plants are dying off, this looks healthy and vibrant. But I've never seen anything like it.
It is flat on the ground growing from the middle and outward and the long leaves feel spongey. Vibrant green with weblike grey lines on the green. Weird for around here.
Unfortunately the pictures are from after I dug it up and put it on the burning pile. I don't like plants I don't know in my horse field!

Click image to enlarge

Re: Unknown plant in my horse field

Reply from Simon Hickmott

Blessed Milk Thistle, Silybum marianum.

Re: Re: Unknown plant in my horse field

Reply from Nicola

Thank you Simon!

Hi Ruth here is Blessed Milk Thistle, Silybum marianum in Shoot.

Hopefully this helps?

Re: Unknown plant in my horse field

Reply from Nic Jennings

If you see another one in your field leave it as this is a very useful liver cleanse for horses. You could pay a lot of money to buy this stuff as a supplement.
General horses will browse it when it is young and fleshy, but mine used to chew it up regardless of the size of the prickles.