My two-horse straight load, bumper pull trailer has a round nose, fixed glass at horses heads.  There are bus type windows on both sides and on both rear doors with two roof vents.  There still seems to be a heat build up problem with the horses sweating a good deal.  This may be normal, I don't know.  Anyway, is there any way to improve ventilation?  Replacing the rounded windows with curved sliders would probably be very expensive, if it is doable. 

Installing two way roof vents would help. They allow either impact air into the trailer, or draw air out in a venturi action. They can be closed to the weather, and are easily adjusted as necessary. They are almost standard equipment in most SL trailers, less so in ST load trailers.

One placed over each stall should assist in alleviating the heat build up. Installation is easy, and they are just bolted into place.

http://www.horsetraileraccessorystore.com/vents.htm

Interesting Gard....I guess I always knew they opened both ways but never put much thought into why they did.  I always assumed that opening forward allowed for direct air and opening backwards allowed for indirect air but never considered that opening backwards sucked air out.

So what is your thoughts on how they should be adjusted based on various situaitons?  On a three horse should the first two be opened forward and the alst backwards to move air in and out?

What do you use to do this?  I know this is probably a good idea but not one that I have done a good job of following.  I have a trailer that has drop down windows with bars, when needing just a little bit of air I have sliding windows that are screened but when needing more air I just drop the windows and have bars.  I know that they have screens available but they look as though they would rip about as quickly as you could install them.

These types of screens are quite durable and easy to install. Make sure to get the zippered models.

http://www.horsetraileraccessorystore.com/window_screens.htm

It would be nice to have some screens that covered the bars that way if I dropped the bars the screen would also come down rather than needing to open a drop down, bars, and a screen to get to the horses.

Interesting Gard....I guess I always knew they opened both ways but never put much thought into why they did.  I always assumed that opening forward allowed for direct air and opening backwards allowed for indirect air but never considered that opening backwards sucked air out.

So what is your thoughts on how they should be adjusted based on various situaitons?  On a three horse should the first two be opened forward and the alst backwards to move air in and out?

If the side windows are opened, the vents can all be set up for a max air flow with the fronts open. This will dump fresh air directly onto the horses. If you just want to evacuate the air through the trailer, set up the rear openings to draw the stale air out.

If it's raining, open the rear part of the vents, so as not to subject the horses to the wet ram air.

If you have the rear door windows open, you will need the side windows or the top vents opened at the rear, to allow the air input to escape.

It would be nice to have some screens that covered the bars that way if I dropped the bars the screen would also come down rather than needing to open a drop down, bars, and a screen to get to the horses.

http://www.valleyvet.com/ct_product_group.html?cguid=30E08115-7B6A-11D5-A192-00B0D0204AE5&ccd=IGO043&gclid=CJ-0vuLvrK8CFUGo4Aod3TxRog