Final answer:
The U.S. livestock industry most known for vertical integration is the poultry industry, with control over breeding, raising, processing, and marketing.
Step-by-step explanation:
The U.S. livestock industry that is most vertically integrated is poultry. Vertical integration means that the industry controls multiple stages of production, from breeding to processing. The poultry industry is known to have a high degree of control over all these stages. This approach contrasts with industries like beef, pork, and dairy, where fragmentation is more common, and different stages of production are often handled by separate entities. For instance, while hay farming supports the dairy industry and is co-located with dairy regions, this does not imply vertical integration. Similarly, the presence of large dairy farms near population centers reflects demand and distribution considerations rather than integration.