nice !!!
i use 50/50 ratio to mix spawn and bulk substrate too but u can certainly use less spawn (which takes more time)
so main thing about horse manure is that it needs to be properly leeched, this is to get the ammonia out of it, and then properly pasteurized
it won't be smelly and it won't be contaminating your substrate any more that coco coir would, if you do the pasteurization right
horse poo is a very rich source for mushrooms (mostly talking about organic fed horses / healthy horses ) but you can also use ostrich manure which is better than horse manure
so over the years i've found there are some ways to boost your work with the mycelium without spending any money, here i use a mix of rye + millets as grain and instead of using distilled water for water content i use a horse manure liquid infusion
so what you do is mix 93g millets + 93g rye + 93g horse manure infusion (boil 50g of horse manure in 2L of distilled water for 60 minutes, top it up to 1L and strain it out to get a blackish liquid) + 36g vermiculite
i put this in jars or spawn bags and PC them in 15 psi for 90 minutes (without soaking or boiling beforehand)
these are turbocharged spawn and your mycelium will love it, better use a mono-culture to get the best yeilds, then when mycelium growth is complete i mix them with 70% horse manure + 30% vermiculite in monotubs and wait for colonization
all this is done in 25C and presence of light doesn't stun mycelium growth
this way is one of the most nutrient rich ways of growing psilocybe cubensis and if you have a good stain that can make use of it (penis envy mono-cultures) you will experience both high yeilds and great potency :thumb_up: