I'd do either/or but not both. At most you only want 25% organic matter and that is a very generous percentage! You can use whatever you have leftover as a topdressing or mulch, however.

And my preference is always with a mixed ingredient compost over an animal manure..

It depends on what is in your topsoil. In this area if you buy bulk topsoil what you get is a mixture of clay and sand run thru a shredder to make a nice spreadable mixture. In that case you would need the cow manure. You don't say how deep your raised bed is so not sure how much to use.

Composted cow manure is a mixed ingredient compost as the product by itself would not be able to be handled otherwise. Much of this product is the bedding used and there is always undigested organic matter including corn kernels.

No manure carries the range of ingredients as does a mixed yard/kitchen waste compost. And why one would need manure over compost for amending any type of 'topsoil' is a bit of mystery. Both are organic matter and both will achiever virtually identical results. I would not like to find any "undigested organic matter" in any composted manure....that would just indicate it is not properly or fully composted.

And it doesn't matter how deep your beds are. You should still shoot for only a modest percentage of OM in your soil mix regardless of the source or the bed depth. You don't just make up the difference in volume with OM!!

gardengal - You need to reread OP's original post and also my response.

OP has two products, a raised bed of "topsoil" and 8 bags of composted cow manure. If that topsoil is "a mixture of shredded clay and sand" then the "composted cow manure" should be used as this will be the only organic material in the raised bed.

Roger take a look at the topsoil in your bed. If it looks like dirt, a reddish brown beige color use the cow manure. If you have rich black topsoil you can still use a little. When an organic gardener uses manure they don't use bags of fertilizer The cow manure provides all the nutrition you will need.

No John, I don't need to reread the OP's original post. They asked whether or not they should add a "multi-purpose compost" to their soil mix. And I answered that question.....one or the other but no need for both. And to keep added OM - whatever product they choose to include - at no more than 25% of the total mix (and a bit less if possible). I also expressed a preference for the compost over the manure because a mixed ingredient compost will carry a much wider range of nutrients than will the compost and will also generally have a better textural component.

It was you that introduced comments about what "kind" of topsoil they were using and that cow manure was the only way to go. What kind of topsoil really doesn't make any difference - by definition topsoil is neither 'rich' nor black - all topsoil will benefit by adding OM. And it really doesn't matter all that much what sort of OM they choose, although fully composted is better than anything very fresh or unfinished.

btw, just adding composted manure or a mixed ingredient compost will not necessarily guarantee the plants will receive all the nutrients they require. Supplementation may well be necessary during the growing season.

They have " Store bought topsoil and 8 bags of compost cow manure" They can either use what they have or go out and buy more stuf and maybe get coronavirus along the way.

If their raised bed is 6 inches high then I'm concerned that 8 bags of composted cow manure is too much. If the raised bed is 12 inches high them maybe it's about the correct amount.

I'm picturing 8 bags of cow manure laying on top of a 3'x8' bed. The bags would pretty much cover the bed. If the bags are 3 inches thick then in my opinion that's too much manure in a 6" deep bed.

My experience with manure goes back to the 1950's when I helped my uncle load, unload, and spread a pickup load of manure on my grandmothers veggie garden.. She had at least a foot of black loam and every few years we added some manure. She never added fertilizer in between. Since then I have never used fertilizer and only once tried side dressing with manure tea. When I tried it I didn't see any results.

When I go for manure I find manure with straw, or wood chips mixed in. It doesn't compost and neither would any corn kernels. There's also the possibility that the manure has neither because the barn has dirt floors and doesn't therefore need bedding. So the organic matter in the manure varies widely. In my opinion the best is with the straw, it's harder to work with, you'd be better digging it with a fork, than a spade.

I think all 8 bags in a 6 inch bed would grow 14 foot tall tomato plants. Been there done that!

edit:

We need to know how high the beds are and the quality of the "topsoil"

" I find manure with straw, or wood chips mixed in. It doesn't compost and neither would any corn kernels. "

In what world do you live that these items will not compost?? ALL organic matter is compostable!! A properly processed compost should have almost nothing in it that is recognizable. And cow manure should be composted or at the very least, very well aged before using on a vegetable garden.

" A properly processed compost should have almost nothing in it that is recognizable"

What I find is that wood chips are very visible. And a manure pile where straw is used for bedding is also obvious. You hold yourself out as an expert, Just once in your life go visit a horse boarding facility, visit a few to get a feel for how the bedding affects the manure. Take a spade with you, dig around, find the old, composted manure. Take a deep breath. This is gardening before fertilizer came in bags.

eight bags of manure is way too much for a 8x3 bed. i would use at most 2 bags, i'd be inclined to use no more than just one bag.

very good composted manure usually won't burn, but most commercial cow manure which hasn't been properly aged, can burn plants if you use too much..

i'd try to get some garden soil worked in with some mushroom compost, or shrimp/seaweed compost (check Agway if you have one locally - they had buy 1 get 1 on their shrimp/seaweed compost).

John, please try not to be so condescending. It is really unnecessary and pretty passive aggressive. And can make you look foolish.

What you describe with the manure pile at the horse boarding facility is not compost....it is just a pile of manure and stall cleanings. If it was fully composted, neither the straw nor the wood chips would be obvious. That homogeneous material is what you might find at the bottom of a pile that has been accumulating for six months or longer. Passive composting.

I have never, ever "held myself out as an expert"!! I just have a pretty detailed education and a great deal of experience. And that includes being a serious horsewoman in my younger days. I am intimately familiar with horses, their poop and what happens to it.