Animals which have a carnivorous diet are not generally considered suitable for food, and the meat of uncastrated adult male animals is often shunned.
The stock bull, early born uncastrated males, or unwanted ‘visitors’ from or to neighbouring farms are the likely culprits.
The receipt specifies the product of a stonehorse, that is a horse uncastrated, a full stallion.
For instance, say that uncastrated men really don't want to be chemically castrated, but once they are they don't really suffer much.
I haven't seen them around for a while, but Gordon has enemies, mostly large ginger uncastrated male cats who live further up the street, and occasionally steal food from the kitchen.