The first winter I had my first two dairy cows, I dried them both off at the same time and I canned and froze milk for the dry period. Then for about six or seven years, I continuously had lactating cows and did not need to find ways to preserve milk. Last winter when we went seasonal with the herd, I froze all the milk needed for the dry period. This year, as I get ready to dry the herd off again, I decided to both freeze and can milk due to my limited freezer space.
Now, before getting too excited about canning milk, I must warn the reader that according to some sources, the USDA does not recommend canning milk at all. Then, there are some sources that seem to feel the USDA approves only of pressure canning milk. You will have to research the information and decide for yourself what you feel comfortable with for your family. Here is a link to Perky Prepping Grandma where the author gives her reasons along with documentation as to why she feels that pressure canned milk is safe. She also provides a link there to the process for pressure canning milk. In addition, here is a link to Mary Jane Toth's instructions for pressure canned milk along with her advice and recommendations regarding the subject. Mary Jane is author of two books on cheese making and milking dairy goats and she and her family operate Hoegger Dairy Supply.
In spite of the warnings, there are a number of family cow owners who still can their milk the old fashioned way in a hot water bath canner. I am not recommending that this method is for you and your family due to the strong warnings from the USDA against it but provide it here as a historical reference if nothing else. Back in the day before Google and the internet, I looked Carla Emery's book THE ENCYCLOPEDIA OF COUNTRY LIVING to guide me in my quest for homesteading and farming information. I am summarizing Carla's recipe for hot water bath canning and including my personal notes:
*Fill your clean, sterilized jars with fresh milk from the cow after straining, leaving about one half an inch head space. (You don't want to pour cold milk into the jars and put them into the hot water as the jars will bust. If you use older milk, it can actually curdle while being processed. It's best to use milk straight from the cow fresh. In the event you don't have that option, I suggest heating your milk to at least 100 degrees before pouring in your jars.)
*Wipe rims clean and place lids and rings on jars and screw down finger tight.
*Place jars in hot water bath canner with jars submerged about 1 inch under water.
*Heat to a gentle, rolling boil and then process for 60 minutes.
*Remove from boiling water carefully, making sure they have all sealed before storing. Be sure to date your jars so that you know how long they have been stored as you use them. Six months is recommended, but I have used them up to a year later.
When milk is processed, it does change color and the flavor is greatly affected. The closest thing that I can compare it to would be the canned, evaporated milk that you would buy in the grocery store. I only use my canned milk for cooking things such as baked good, gravy or puddings. When used in recipes, it is wonderful but isn't really the best for drinking.
The best way to preserve milk for drinking is to store your fresh milk in freezer safe containers or bags and store in the freezer. Frozen milk is best used within six months. A lot of people are put off by the texture of frozen milk and if that is something that is of a concern to your family, you can warm your milk up to body temperature (99-101 degrees approximately) and stir vigorously. This will give the milk more of the texture that you are use to when drinking.