[gods-child]

long before tetanus jab for man and critters my family on a long line of generations have been using horse-manure for gardening and to my knowledge there has not been any issues as long as the horse-manure is well composted or well-rotted over 1.5 ~ 2 years at least

be careful and ask questions of anyone who you may be looking to get horse-manure from as some pesticides cannot be composted or well-rotted out

here are some resources thereof

https://www.rhs.org.uk/soil-composts-mulches/weedkiller-in-manure

https://www.hse.gov.uk/pesticides/using-pesticides/general/issues-associated-with-the-use-of-farm-yard-manure-containing.htm

https://extension.oregonstate.edu/crop-production/soil/herbicide-carryover-hay-manure-compost-grass-clippings

https://content.ces.ncsu.edu/herbicide-carryover

hope this helps

bona-fide