Hi!

I am a forage Agronomist; probably not the one most appropriate to answer this question. (But it is likely that no other University or Extension Specialist is either - for this particular question.)  I will respond based on my past farm experience and observations over the past few years.  Probably the best answers will come from other horse owners.

I will separate the question between 'breaking up manure' and 'de-thatching the pasture grass'

'breaking up manure'
As you describe, the Fuerst harrow (chain harrow)  is probably too light-weight to break up dry horse manure clods well. 

Alternatives.....
A 'spike-toothed harrow' -- heavier, more rigid, with railroad spike-like spikes that can be adjusted form 'flat' to nearly vertical; and they come in varyng widths --- might break up manure clods better.  If you use one of these, you should experiment with tooth angle.

Hay rakes......  Hay rakes vary in 'aggressiveness'.  The 'wheel rakes' would probably not be very successful at breaking up resistant manure clods. The pull-type, side delivery rakes only slightly better.  The PTO-driven 'parallel bar rakes' would probably be the most aggressive.

'de-thatching the pasture grass'  (I am not sure what your objective is --- disrupting the sod/soil surface ? dislodge dead grass stems? ???)

As you describe, the Fuerst harrow (chain harrow)  picks up debris, and you have
already 'fiddled' with extra weight and recognize its limitations.

Alternatives.....
The 'spike-toothed harrow' (described above) can be adjusted form 'flat' to nearly vertical.  In the flat setting, it will not likely disrupt much sod or thatch.  and at its extreme /vertical tooth setting would act more-or-less as a rake.   - If you use one of these, you should experiment with tooth angle.

Hay rakes......  Hay rakes are designed to gather/collect loose vegetative material, and if anything, will pick up more 'debirs' and accumulate it in 'windrows' much like in a hayfield.    They vary 'aggressiveness', and can be adjusted up and down to scratch more or less thatch.    If that is your objective, then the PTO-driven 'parallel bar rakes' would probably do it best.

thank you so much - your response has been the best/most enlightening - I like knowing" reasons why" - after much time on the internet "researching" this, I was leaning toward the spike type, too…..I want to break up clod of manure and drag up the dead debris and leaves to allow some air/sun/rain to penetrate ….thanks again for your complete answers!  Pixie

One more question - in my internet surfing on this topic of harrows, I came across "landscape rakes".  I've seen these at our local Bomgaars by Northern Tool & Equipment.   I these would be too aggressive unless you could set the height and also might "pickup" too much debris instead of spreading it out (?)

another type I have read about - spring tooth harrow….rather like the Landscape rake but tines are off-set so they don't pick up and hold debris and the tines are flexible.
What would you think of one of these ?  Mostly seem to be an "old-time" piece of equip. but seem to be somewhat available new.   

RE: other rake types

Landscape rake.....  would 'rake up' significant litter/debris; and would non likely
                                  break up many horse manure clods - just roll them along.?

Spring-tooth harrow .....  would 'disturb/rough up bare soil ares/ and likely dig up
                                       random liming sod clumps--- and would not likely break up
                                       many horse manure clods ( just move them laterally).
 
S. Barnhart

OK - pretty clear that the spike tooth is the way to go

know anyone who wants to buy a lightly used Fuerst flexible tine harrow?  :)
thanks again for your help, Pixie