Per Wikipedia; Latigo leather is cowhide leather that is combination tanned. First it is chrome tanned, then it is vegetable tanned.[1] Before modern combination tanning, latigo had been combination tanned with alum and gambier.
Per the Buckle Guy; English Bridle leather is an authentic vegetable tanned cowhide/steerhide that is made from the highest quality English animals and products. It is dyed in drums in order to develop deep, consistent colors with waxes and tallows. After the dying process, the leather is then hot stuffed with pre determined amounts of spew on the grain and flesh, giving it the English feel. Upon completition the leather will be stiff, though with the proper care and an ample amount of break-in time it will become soft and supple with a lot of strength.
Per Weaver Leather; Stuffed with heavy tallows, harness leather offers exceptional weight, thickness, ease of cutting and durability. Its self-explanatory name sometimes expands to include collar and saddlery leathers. All harness leathers are generally made from vegetable tanned cattlehides.