I have horse coming up from the south to the north where are in freezing to below freezing temps. I know horses in the south still grow a bit of winter coat but not to the extent of northern horses. She is also not currently blanketed. I’m going to order her a blanket/neck combo. Should I go with a heavy weight or a medium weight? I instinctively think the heavy weight but I'm not sure how much winter coat to expect her to have?

And what type of blanket should I have her shipped in? The hauler will probably not be able to change the blanket out as they travel north. Would a winter blanket be too hot in an enclosed slant load traveling from southern weather to northern weather?

Any advice would be greatly appreciated.

Where in the south and where are you headed to in the north? That makes a big difference, a blanket upon leaving will probably be too heavy, arrival depends on the temps, you could probably put a sheet on her to start with depending on all the above information.

I agree. That trailer will stay pretty warm with other horses in it and it being enclosed. If she has a bit of winter coat I think I would leave her naked in the trailer and have a heavy weight with a neck cover ready for her when she unloads. If she is at your place to stay you might as well invest as she will probably need a blanket next winter too. My gelding that came to me from Alabama just does not handle the cold well. He loves his winter blanket the minute the temps are below freezing. Especially if there is any wind at all. I have been told 3 winters for their bodies to adjust to it if they are lifers from the south.

It depends. How much coat does she have now? Horses here in South Georgia have anywhere from short/thicker coats in winter to longer teddy bear coats. Just depends on the horse. Regardless, I'm not entirely sure I'd blanket heavily on the way up, but definitely upon arrival. Our horses occasionally experience temps in the 20's for a few hours at night and are just not used to anything harsher. Even my guy with a teddy bear coat would probably need a blanket in a northern state. 

Where "North" is she headed?  I bought a horse in Texas and hauled him home to Upstate NY in December 1 year.  Blanketed him for the Texas weather on way home.  Once to NY he wore a heavy weight blanket.  Sometimes 2 as it was that cold here and he had no winter coat whatsoever.  Nicknamed him Shivers as he would stand in his stall with 2 winter blankets and shiver.  He adapted well though.

I have one that has been barn kept in coastal NC for the past three years that is coming home to NVA Feb 1 for a 6 week rest. I bought him a midweight necked blanket for his stay. It's only a 150 mile move north, but he's very slick and barely thickened hair. I won't put a heavy weight on him because then he'd have to be neked if it was over 40 degrees (which is most days). 

I personally don't like the combo blankets - I prefer to have the regular blanket & then the separate neck cover - that way, they are not "stuck" with that neck cover on all the time.  I like the medium weight blankets & then maybe a liner or BOT sheet to use when it's extra cold.  I've had best luck with Schneiders blankets www.sstack.com .  Their warranty has been great & so is customer service.

Thanks for the advice and experiences. This is this first time hauling one up in the winter and it has stressed me right out! I ended up sending a fleece cooler to put on her as needed. Then I ordered to arrive here for when she comes off the trailer a lite and a medium turnout and a stable sheet for under the medium if needed on really cold days. I also bought a detachable hood. It was all pricey but I think will be well worth having the interchangeable blankets. Luckily Smartpak was running a blanket sale!