The origin of butter is still under discussion but many people believe that it’s discovery is (at least partially) linked to equestrian pursuits:

Butter was probably first created accidentally when whole milk carried in skin bags was carried by horseback and naturally “churned” while traveling over rough terrain. The first documented mention of butter making was in the sacred songs of the dwellers of Asiatic India, dating back to 1,500-2,000 B.C.E. There is historical mention of ancient tribes creating primitive churns by horizontally agitating cow, yak and horse milk.

Source: http://www.webexhibits.org/butter/countries-india.html