Organic milk sales have cooled as the very shoppers who drove demand for the specialty product not long ago move on to newer alternatives, leaving dairy sellers and producers grappling with oversupply. A yearslong surge in demand prompted food companies and dairy farmers to invest in organic production, which requires eschewing pesticides and antibiotics and allowing cows to graze freely. Now, organic-milk supplies have ballooned just as demand has stalled. Many shoppers have moved on to substitutes such as almond “milk,” which contain no dairy.Packaged-food companies that invested in producing organic milk are cutting capacity or looking to turn it into cheese or other products. Grocery stores that rushed to stock organic milk have eased purchases and allotted more dairy-case space to plant-based alternatives. Dairy cooperatives are slashing prices paid to farmers, setting quotas and even selling organic milk as conventional dairy.