Midwest Growth Partners, a West Des Moines private-equity fund, has purchased Maytag Dairy Farms, the nationally recognized maker of Maytag blue cheese, according to a release. Midwest Growth Partners didn’t disclose details about the purchase, but said it was a “major investment” in the 78-year-old Newton-based dairy. All employees of Maytag Dairy have been retained through the sale, the company said. Maytag employs 40 full-time employees and 40 part-time and seasonal workers. The dairy will use Midwest Growth’s investment to pursue several initiatives, including expanding its production facilities, exploring new products and boosting sales, the company said.