I have guinea pigs who live outdoors and have been asked to share my experience so here goes.
My girls have lived outdoors for 2 winters now and this will be the third (first time for my 2 newbies).
Mine have been perfectly fine BUT it has taken work to make sure they are kept warm and it must be done properly.
I layer the entire hutch floors with layers of newspaper followed by a layer of shavings and a layer of hay in the living area. In the sleeping area they have layers of newspaper followed by mountains of hay that they can snuggle in to. They also have fleecy cosies and beds to snuggle in to and I use snugglesafe microwavable heat pads
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Their hutch is placed in a well sheltered area of the garden and they have a waterproof rain cover that keeps them protected from the wind and rain.
Last year, I fixed a thick fleece blanket over the wire mesh of the hutch over night to keep the chill out.
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I think that guinea pigs can live happily outdoors over the winter BUT it must be done properly. If I could, I would have them indoors over the winter but it just isn't practical for me due to lack of space and hubby being allergic. However, if the pigs really were suffering, I would bring them indoors in a make shaft cage or something but luckily, I haven't needed to yet.
They had a scratch and newton hutch snuggle last year but it went to a new home along with the old hutch and they do not do one in the size I need.
If you intend to keep your hutch outdoors over winter, the outside needs to be well insulated as well as things to keep the pigs nice and toasty inside.
Also last year, my husbands friend made a wooden shelter that the guinea pigs hutch sat under to provide even more protection from the wind and rain.
If you are planning on rescuing some guinea pigs at this time of year, please be aware that a rescue will probably want to know where you intend to keep your guinea pigs over the winter months and some will not re home to a home where the guinea pigs have not had the time to adjust gradually to outdoor conditions. For example, my 2 newbies have been with me since March and the beginning of June so started off outside in the warmer weather meaning that they have had time to adjust to outdoor living before the colder weather hits.
Last winter, I made sure I woke up early so that the girls had a warm snugglesafe for daytime use and plenty of fresh warm bedding etc.
If you intend to house your guinea pigs outdoors over the winter, please do everyting that you can to keep them warm and make sure you have an alternative just in case they get to cold