There is no reason why not as long as it is well rotted. Just make sure not to put it right up to the 'neck' of the plants by leaving 3 or 4 inches around them. 2-3 inches deep would be ideal to.

If it were me I'd be digging it in even if it is well rotted. You also need to be sure that the grass/hay/haylage the horses were fed on had not been treated with that herbicide which survives passing through the horses gut and can cause problems in the soil. Also be aware that there can be antibiotic residue in horse manure.

I read that on the internet MG, what would you recommend instead? I have a lot of Heucheras, Clematis, Honeysuckle and Crocosmia amongst others.

Is there anything that will help protect and maybe enrich the soil, all my plants are in large pots and containers.

Containerch., if your plants are all in containers, using composted manure is not an option - this is intended for use on open ground only and is not suitable for use in pots. I'm afraid you're stuck with liquid forms of nutrients - perhaps liquid seaweed, etc., and maybe small bark chips on the top of the pots. Do not, though, use any feed on any plant at this time of year, it will have to wait till spring.

I can only echo what has been said regarding pots and containers.

I have a few horse riding academies around the area with "Free Manure" signs out front. I would never use fresh manure for my garden. If the manure has that horsey smell it is too fresh and will totally burn your plants.
Composted horse manure will have a damp forest floor smell and is fine to use. If you are worried that the
manure still has some viable weed seeds in it, shovel out a pile of the amount you are going to use on top of a layer of newspaper or weed screen material wide enough to accommodate the spread out pile in a suitable sunny area. This way, viable weed seeds will generate and you can then eradicate them with hand picking, hoe or raking or using a herbicide. If you use a herbicide, when is it safe to plant? The answer to that is: READ THE LABEL and FOLLOW THE DIRECTIONS!

Thanks to all for your helpfull answers.

I will get some bark chippings today, then wait untill the spring to get some liquid feed.

Gosh there is a lot more to gardeding than I thought.

Grateford it isn't the possibility of weed seeds in the horse manure that is a worry but the presence of a particularly strong herbicide which survives the horses digestive system and is still active in the dung they produce. This leads to distorted and stunted growth in plants. Many folk who have allotments in the UK have had problems with their vegetables over the past year or so. An allotment society will often buy enough well rotted horse manure for all the allotment growers to use as this means they get a better price. It is only months down the line that they discover their veg. are not growing well... the herbicide having caused the problem. It can take years to clear from the ground.

Moongrower's right - its from the use of Kibosh which kills off two weeds dangerous to horses - but it passes through their systems and out the other end and then poisons your plants/veggies when you apply it to your ground, composted or otherwise.
But for the questioner, this is largely irrelevant, since his gardening is done in pots, not the soil, so manure is not an option.
As a note of interest, Moongrower, I think that the big gardening centre chains have stopped selling composted horse manure - when I went to get some recently, they were selling composted 'animal' manure instead...

Would make a lot of sense Bamboo... there must be a lot of unhappy gardeners. Thanks for reminding me of the name of the herbicide had a senior moment and couldn't remember it.

I think I read recently they'd changed its name as well, but I can't remember whether Kibosh was the original or the new name...duh!

lol

Bamboo, when I went to the GC today to get some bark chippings, they had pallets piled high with bags of horse manure.

It was seeing it there on my last visit that prompted my question.

Buyer beware!

Interesting, Container, because, as I said, my Wyevale had only 'animal' manure ... I'd certainly be asking whether their product was guaranteed to be pesticide free before buying...