COCHRANE, Wisconsin — Dozens of calves groaned as Hermenegildo, a young Mexican farmworker, wheeled out a cart with bottles of milk. He attached the bottles to the wood pen of each calf, walking up and down the row as the animals guzzled the milk in minutes. The 600 cows on the dairy farm produce 5,000 gallons a day, which are trucked for processing into cheese at a plant owned by a Minnesota cooperative. Farm owner John Rosenow credits immigrant labor with sustaining his business, estimating that at least 90% of the workers on Wisconsin dairy farms are unauthorized.