Beginning in the 1920s, du Pont began breeding [[Holstein Friesian cattle]], originally bred in the north of the Netherlands and Germany. His father approved of this endeavor, telling him “That’s a splendid idea. It will cost less than maintaining a yacht, and it may result in some good for humanity.” On tax returns and other documents, he often chose to identify his occupation as "farmer."<ref name="harvard" /> Du Pont became recognized as one of the premier dairy cattle breeders in the United States, and the Winterthur herd dominated national awards issued by Holstein-Friesian Association from the 1920s until du Pont's death in 1969.<ref>{{Cite journal |last=Fleming |first=E. McClung |date=1964 |title=History of the Winterthur Estate |url=https://www.jstor.org/stable/1180465 |journal=Winterthur Portfolio |volume=1 |pages=9–51 |issn=0084-0416 |via=[[JSTOR]]}}</ref> Following his death, the Winterthur Museum sold du Pont's herd ofto dairyfocus cattle, prioritizing theon presentation and preservation of du Pont'sthe collections and gardensestate.