Anwer:
According to information from the farm, these holes are used to check and evaluate the health status of the dairy cows at each time. From there, people can provide the right type of food, bringing the highest milk yield and helping to prolong the life of the cows.
Each dairy cow undergoes surgery to create a large cavity in the abdomen, then a tube is installed. This tube allows the farm staff to directly put their hands into the cow's stomach to handle the food if the cow's digestive condition is difficult. They can pour medicine directly into the stomach to help the cow's digestion easier.