I laid down horse manure, some new and some aged. Can I harvest the mustard greens that have sprouted without waiting?

It's a gamble. The National Organic Program states that in a certified organic farm, any manure that isn't hot-composted cannot be applied to a field within 120 of harvest for any crop where the edible portion touches the soil (ie, carrots), or within 90 days of harvest where the edible portion doesn't touch the soil (corn). This may be overkill, but there you have it.

thanks. I knew I should have harvested before I spread that!

Animal manures are known to have several disease pathogens in them, E-Coli, Listeria, and Salmonella are those that have been in the news a lot in the past several years (since the Reagon Administration cut the USDA inspectors) and that is why it is strongly suggested that manures not be put on your garden sooner that 90 to 120 days and is why it is alwasy best to properly compost any animal manure before putting it on your garden.
Since several hundred people have died from foods contaminated with one of those diseases why would anyone want to potentially expose themselves and their family to those diseases when the means of preventing that is so simple. I would not consider taking simple precautions as overkill.

Altho the "old people" manured and picked soon after, I think the prevalence of diseases, toxins, antibiotics, etc. in our society now makes it prudent to compost, wait, etc. when dealing with fresh manure. The "up" side is that cutting the mustard greens and letting it lay adds to the organic matter of your garden.

As someone who makes ample use of the manure from her 6 horses, I have to agree that it's best if you don't harvest your newly manured crops.

I dump/spread manure & used stall bedding over my garden over a period of about 2 months (early Dec./early Feb.). Turn under a few times & then leave for spring planting. Since we have a relatively mild winter with lots of freezes & thaws, everything is pure compost by planting time.

That said, I definitely would not harvest & consume anything sprouting out of freshly laid-down manure - fresh or aged. Until it's turned to indistinguishable compost, I don't consider it safe.

What about mice and rabbits and such "composting" your garden on the fly?

Any dangers there??

Those amounts are so minimal, they're not worth worrying about.

I'd probaly pass on eating the greens to be safe but if ya had any chickens ya could feed the greens to them or atleast put them in a compost pile.
In my opinion 120 days is overkill, 90 days is plenty is plenty and could get by with a little less and be fine. I put chicken bedding straight on the garden but where applied I usually wait around the 90 day mark before planting anything except with corn. I add manure right before and sometimes after I plant my corn rows and have had no problems.

I'm sure to catch flak for going against popular opinion here... but you did specify horse manure. The outbreaks of E-coli, etc. that Kimm1 describes usually occur with livestock raised in confinement and fed high-grain diets which their systems are not designed to digest.

If it were me, I would have no problem with harvesting your mustards, making sure they were washed thoroughly and cooked long enough to kill any potential bacteria. Still, it's always a good idea to compost manures, not only to kill pathogens but also to kill hay and grass seeds that will sprout if you spread it new.

The pathogens that cause E-Coli, Salmonella, and Listeria, as well as tetanus have been found in horse manure as well as that of ruminants and are present in human excrement as well.
Common sense should tell anyone that properly composting all manures is the prudent thing to do.

Yes composting the manure is best and much of time I do but sometimes I add it straight to the garden and till it in. This is usually in the fall when it will have many months to start to break down. Also the manure that has built over the winter is spread on the summer crop part of the garden and tilled under when it's dry enough in the spring but by the time I can plant that area it has broken down enough where it should be fine.