Unless you live in a place where the weather literally never changes, you will always have to prep for changing seasons and the "bad weather" that comes with them so your mini cows make it through healthy and happy.
After our second blizzard of the year on Jan 8 and today it's 13 degrees with -20 windchill, this seems like a great time to talk about winter prep.
The gist of winter prep is this: The things that keep your mini cows healthy all year are the same things that you need to think about to prep for winter weather: 1) Food, 2) Water, 3) Shelter.
Other than these three, you can also make sure your mini cows have the right BCS for heading into winter. A healthy cow will get an "ice/snow cape" during winter precipitation that actually helps them keep warm, while a less healthy cow may not get a proper ice cape;
Food
Mini cows are ruminants. In simplistic terms, this means that the plants they eat go first to the rumen where it is fermented, belched up, and swallowed again. (Fun fact: this is where the colloquial term "ruminate" comes from when it means to think on. When cows are chewing their cud, they're ruminating!)
This entire process creates heat, which means that during cold weather cows will eat more than usual because they're staying warm.
Bottom line, during cold weather in general and especially during frigid weather, make sure your mini cows have access to free choice hay so they can keep warm, or otherwise be sure you're throwing hay multiple times through the day.
Water
Cows' water needs don't necessarily change in winter. Some sources say they'll drink more when they're eating more, which makes sense. I find that during cold sunny days they drink more, and during cold snowy days they drink less.
The main winter prep related to water is making sure water is always available. This is the same as usual. This means troughs full and not frozen. For most people, this also means making sure the hoses and hydrants aren't frozen.
To keep troughs unfrozen, it's common to use a tank deicer, a freeze-free automatic waterer (common brands are MiraFount, Ritchie, Bar-Bar-A, and Drinking Post) , or something like a freeze miser with float valve.
We use tank deicers, so I'll talk about them here. But one day we will have automatic waterers at every pasture!
Tank deicers are devices that you plug in and put in a water trough. They generally are thermostatically controlled to only come on when the temp reaches a certain point. There's two primary kinds -- a fully metal kind with a cage that sits on the bottom of the tank like this one from Farm Innovations, and a floating deicer with a plastic cage like this one from K&H products.
The considerations for choosing a deicer include
What type of trough you have -- if you have a metal trough you can use any kind. If you have a rubbermaid style trough you need one that won't melt the trough
What is your weather zone and how cold do you expect it to get -- The colder it will get, the higher wattage you'll need. The K&H products have a nice climate zone guidance map
How big is your trough -- the larger your trough, the higher wattage you'll need. Most deicers are rated for specific sizes.
The last point about deicers -- they plug in so they require electricity. You can do the math for your area and electricity costs, but a 1500 watt deicer costs about $1.50/day to run during winter. Our first winter I was shocked when our electric bill went up $200/mo!!!
Shelter
Just like in hot weather, mini cows need shelter to get out of the wind and any pelting rain or snow. The minimum is a windbreak, but with unsettled weather most ranches or farms have run-ins.
Some people wonder if they need a weather-tight barn with a heater. The answer realistically is no. In fact, if you have a barn where you will lock in your mini cows, you need to make sure there's plenty of ventilation -- without proper ventilation cows are more prone to pneumonia.
On Bossy Boots Ranch we have 3-sided run-ins that are big enough for our mini cows with horns. We have our pastures split up enough that everyone can get into a run-in if needed.
An important part of the shelter is bedding because that allows them to create warmth as well. This is especially important for calves, where the rule of thumb is that when they lay down you shouldn't be able to see their legs. Here's a great FB post by Dr Hake Calf Vet.
There's several options for bedding that include straw, shavings, sand, combo, etc. We have simple run-ins in the pastures, and we use straw because it's inexpensive and warm. Through the winter months we do deep bedding method where we partially clean and then add fresh straw to the top.