Even though we are in South Louisiana, where the weather is milder (if not downright oppressive) most of the year, we still have to protect our pets from the winter. Their bodies are acclimated to the warmer climate of our local area and the sudden change in temperature can affect them just as much as it affects us. Of course, this is most important in outdoor pets. Anytime it looks like the temperature is going to drop below 40 it is imperative you offer a dry, warm place for your pet to stay. Have enough water and food especially when their water bowls have a chance to freeze over.
Being dry is important, because once their coats get wet they can no longer act as an insulator and your pet can get hypothermia. This holds true even at temperatures right above freezing. Really young and older pets should not be outside at all during cold weather. The main reason behind this is that they have an even harder time to maintain their body temps. Their bodies do not have the fat or metabolism to stay warm when the temperature plunges.
If you plan on bringing in a strictly outdoor cat during the winter, it should be well acclimated to a garage or other area several months prior to winter. Pet houses, wooden, cardboard boxes could be made to keep the cats out of the weather- just make sure the bedding stays nice and dry and protected from the wind and rain. These types of shelters will give your feline friend a sense of security. An easy gauge in helping you decide if you should do something for your pet is to think smartly, if you are cold your pet is cold as well.