While horse hooves were historically used for glue, this practice largely declined in the 20th century with the advent of modern synthetic glues.
Here's why you might be thinking about this:
* Ethical Concerns: There may be some ethical concerns about the sourcing of hooves from horses, particularly if they were obtained from animals not raised specifically for this purpose.
* Environmental Concerns: Modern glues are often derived from petroleum-based products, which have environmental impacts.
* Historical Context: You may be thinking about a time when animal products were more prevalent in manufacturing, and concerns about animal welfare were less prominent.
In summary, there's no historical evidence to suggest that using horse hooves for glue was ever illegal.