The first question seems irrelevant-- what does it matter if they’re “meant” to be or not? If they’re removable, which obviously they are, and if it’s what you want to do, what is his actual objection? Is he arguing that it’s somehow damaging the curtain or trailer to do so? Or that it does not affect airflow?
Or is he just (I’m reading between the lines here, and maybe completely off base) discounting your horse expertise and thinks your horse doesn’t really need something that you know he does. But rather than have THAT debate, he is asserting technical reasons, and you’re allowing yourself to be sucked into proving / disproving those technical reasons, when the real answer could just be “because based on my expertise and experience, trailering in the summer without curtains is better for my horse. Next topic.”
As for the holdback latches, you could contact the trailer dealer or manufacturer. I would phrase the question in terms of “are these latches rated to securely hold the curtains at highway speeds?” But ultimately, this second question only becomes relevant if we assume that you are somehow not allowed / not supposed to remove the curtains in the first place.
Should go without saying but yes, having a large opening in the trailer either covered or uncovered will dramatically affect airflow within the trailer, and on a hot day, reduced airflow will reduce your horse’s ability to cool himself via sweating. The KY Equin Research study “Ventilation in Horse Trailers” may be useful, if he needs to be convinced by outside expertise how much airflow matters: [INDENT]“Even at the highest speed and with all windows and vents open, average air exchange rates were only about half those recommended for stabled horses. Although outside temperature never exceeded 28º C. (82º F.) during the study, heat stress conditions (defined as air temperature exceeding 30º C. /86º F.) were observed inside the trailer. Horses in stall 1 routinely showed more sweating than those in other locations.
What do the results tell us about keeping horses healthy during transport?
Based on analysis of data, the trailer used in this study was judged to be under ventilated.
An independent but similar study found less variation of air exchange by location when upper rear trailer doors were removed. Ideas for providing better air exchange and minimizing heat stress of transported horses include increasing window size and opening or removing upper rear doors. Owners should look for maximum ventilation when they are comparing trailer models prior to purchase. In this trial, data were collected for only two conditions, empty trailer or trailer holding four horses. When four horses were transported, air exchange rate was lower in front stalls than in rear stalls. Putting the smallest or leanest horse in the first stall might be a way to avoid overheating during transport.It is safe to assume that increased air exchange minimizes the buildup of dust and mold spores in trailer air, but drafts due to increased speed can blow particles of dust, hay, and straw through the trailer. Putting fly masks on transported horses can help to keep dust and airborne material from causing eye injuries.”[/INDENT]
