safety · trailering

PSA: Always double-check your trailer hitch yourself

On one level, this is pure common sense.

On another level: how easy is it to say “so and so knows what they’re doing, they’ve done this a million times, it’ll be fine, I trust them.”


Never. Not one time.

If you are the one hitching up your truck to a trailer – whether yours or someone else’s – you do the last double-check yourself. Always. No ifs ands or buts.

First story:

Some years ago, I was hauling two horses to King Oak. Neither horse was mine. Both horses were owned by experienced owners and riders who had themselves hauled horses many times. So, I saw myself purely in the driver’s role. I hitched up and presented my trailer; they put their horses and equipment on it. The drive was fine.

We arrived at King Oak, and the first horse unloaded just fine and went off toward her stabling. The owner of the second horse dropped the butt bar and asked her horse to back. He didn’t. She asked several more times, growing more insistent, and then he backed. Hard. Fast. And…he broke his halter, because he was still tied to the trailer. The owner had never untied him.

He rocketed off the trailer and turned and in a split second I reached up and grabbed his nose with my right hand and pulled down. He was so relieved to have someone in charge again he stood quietly for me.

That was the occasion that caused me to make my first personal rule about hauling: I’m always the one to check the horses before we go, and the first to check them when we get there. Totally fine if owners help – in fact, I prefer that they do! – but before I put my foot on the gas pedal, or before I drop the trailer gate, I want to be personally, finally, reassured that all my equipment is correctly placed and functioning as expected.

So let me now tell you the second story that has sparked my new rule. I admit: I had a moment of laziness.

A few weeks ago, I used my truck to rent a car trailer from U-Haul and then used that car trailer to haul a 1978 VW bus back to work for a new thing we’re doing.


It was a very long and very cool day and the moral of the story is that people should hire horse girls ’cause we get shit done, and we own the equipment with which to do it.

I arrived at the U-Haul dealership early in the morning, after having woken up and driven for nearly two hours, after not a whole lot of sleep. I let the U-Haul guy hook up the trailer because it was a type of hitch with which I was less familiar.

Obviously, I can do the chains and the electrical and all that jazz, but it was the coupler itself that I hadn’t personally used a lot. So I let him do it, and then we tested the lights, and then off I went, driving another 1.5 hours north on a well-trafficked state road to get to the farm where I picked up the VW bus.

When we arrived at the farm, we had to unhitch the trailer for various space and logistical reasons. And the hitch would not come off.

It turns out that the U-Haul guy – who, one would presume, hitches up trailers all the live-long day, had not properly seated the coupler on the tow ball. Instead of sinking down and sitting home on the ball, then locking onto the ball, it had been perched on top of the ball and then the lock was engaged sort of…into the ball itself. So it was good and stuck. It took us 15 minutes of rocking the truck and swearing and jiggling to unstick it.

This is not a picture of the poorly done hitch; this is correctly done. See the brass colored piece just under the hitch? This is it correctly engaged in locking on to the ball. Now picture it about 1″ higher and sort of biting into the ball itself. That’s what I drove 1.5 hours with.

The trailer was unloaded, I never went above 50, and that coupler was good and stuck, but holy shit it could have gone so bad if I’d been going faster or hit a good frost heave. SO BAD.

I was speechless when we discovered what had happened. Thankfully, I was still sleep-deprived and under-caffeinated, so while I was able to react and fix things the real horror of it didn’t really sink in that day and I was able to haul the 2.5 hours back home without incident.

But yeah.

Don’t be me.

Be the last person to check your hitch, yourself. Don’t ever, ever trust another person to double-check it. Not even people who should have all the expertise in the world. Learn from my dumb ass mistake. Though I had previously mostly followed this rule, it’s now ironclad in my brain. My equipment, my responsibility, my final check.


So Long, Farewell

This morning, I delivered my trailer to its new home.

one last adventure.

I have really mixed feelings, but overall: it was the right decision at the right time.

I finally got through to the fiance last night by comparing it to selling his favorite hockey stick. He looked completely horrified: “I’d feel naked!” Yep.

We did have one last adventure together, the trailer and I: I got mildly lost after failing to follow the very good directions provided – and realized that I had no cell phone service and thus no Google Maps to bail me out. I three-pointed over railroad tracks to turn around, made it under a low bridge by inches, and then got up the right hill to deliver it to the right farm.

best copilot.

I also would like to state for the record that I am really fucking good at hauling that thing. I got it hitched up in less than 2 minutes flat, after my first backup put the ball 2 inches too far to the left.

Second try:

Arya and I stopped for McDonald’s on the way home to celebrate, and now she is napping and I am blogging. I have to clean every inch of my house today, and then I am declaring a hiatus on renovations until after the wedding, so hope to get back to actually blogging about my actual horse soon.
co-piloting is hard work.

adventures with the vet · stupid human tricks · trailering

Puttering Around – Heel Scalping, House Renovating, and Life Changes

Last night, my trailer sold. I put a relative minimum of effort into advertising, listed it at a really good price, and answered 2-3 emails a day for the last 3 weeks. Last night, a young woman about my age came over, and saw all its virtues and its vices clearly. She was nice and cheerful and has a young Thoroughbred mare that she’s starting to event. It will be her first trailer.

I am really, really sad, because for a long time that was mine, my ticket to the world beyond, a thing that I loved and slaved over and angsted over and took pride in. But: it is going to exactly the right kind of home, and I realize it is ridiculous to be sentimental about “the right home” for a piece of farm machinery, but I am much happier with this than I would be if it had gone to be someone’s utility trailer or left to rust out on the hill.

The money will go into Tristan’s emergency fund and to start a seed fund for a new trailer, someday. I might take some of it and install a gooseneck hitch on my truck, as I have the possibility of borrowing a gooseneck rig should I want to haul out places.

Not much else exciting to report. Tristan scalped his RH sometime last week, and you’d think that a horse would only be so idiotic/athletic/talented to do such a thing once – but you’d be wrong.

He kept opening it again and again. Each time I went out it would be pouring more blood and covered in a thick layer of shavings dust, no matter what I did to cover it up: Corona, Swat, Alushield.

Hannah was up this weekend and I put her to work mercilessly both in my house and at the barn and after a lot of back and forth as we stared at his foot and marveled that he was still knocking it (seriously, HOW?), I suggested Wonder Dust. It’s not my favorite, but a thorough re-read of the label did say that a) it was ok to use on open cuts and b) it would work as a styric, aka a blood-clotter.

We were both deeply ambivalent, having mostly used it as a preventative for proud flesh, but I squirted some on, covered it in AluShield, and crossed fingers.

Aaaaaand…it worked! The next evening I went out and wiped off a clean, non-bloody heel that was showing evidence of healing around the edges. I think we’re in for the long haul, as it is both circular and large, and neither of those things suggests quick healing, but it’s at least on the mend now.

I haven’t yet put him back on the longe to test soundness – I’ve been so busy with everything, I have no time to really ride anyway – but I will probably do that tonight or tomorrow.

We’ve also turned the corner with his white line & thrush problems, and his hooves are firming up and growing cleanly again. We’re having some communication issues with the new farrier, which I’m not thrilled about, so I’ve been using a rasp to back his toes off a bit and help him out so he doesn’t stretch the white line further.

We had a good weekend of dog-tiring and drinking and eating delicious things and working on the house. Huge, huge progress on lots of projects in the last few days, and today is a holiday for me so I’m going to plow ahead on a few more.


Hard Decisions: Selling My Trailer

I bought my truck and trailer in the spring of 2008. I had saved up money, and I was expecting to head off to grad school in the fall. Possibly anywhere in the whole country! I scoured Craigslist and all the classified ads I could find, and I found an older, serviceable truck and trailer that I loved. The idea was to put my own belongings in the truck, and Tristan’s in the trailer, and away we’d go! It didn’t happen quite like that.

I loved being a person with a rig, that tantalizing possibility. I loved having the extra storage space in my trailer.

Tristan in the background, Tucker in the foreground.

I’ll be honest: I hated driving it. Hitching up the trailer and then loading my horse in sent every single anxiety demon in my brain into coke-fueled overdrive.

I am a great hauler. I am cautious, steady, smart, and I can back that entire rig anywhere. I am prepared and experienced. But I still spent every trailer hauling drive white-knuckled and nauseated. I couldn’t sleep the night before. I am insanely jealous of people who just hitch up and go. It seems so free.

So I’ve always had a love-hate relationship with my rig. It was such an incredibly useful thing to own. Such freedom and so many interesting things were possible!

However, the combination of my life, my schedule, my finances, and my aversion to hauling all mean that I haul out only once or twice a year. I know there are lots of you who would go somewhere every weekend. I wish I were like you, but I have to accept that I’m not.

Last night, I brought up a tupperware of Tristan’s winter blankets for storage. I opened the door, looked in the trailer, tossed in the tupperware, and had a moment of blinding realization. It was time. After two or three years of hemming and hawing, I was ready. I felt it in my gut. I am desperately sad about it, but I also have no doubts at all.

So, I have sent out some emails this morning. Over the weekend it’ll go on Craigslist. It’s time. I’ll set aside the money I sell it for (I’m not looking for a lot anyway) as seed money for the future, and go back to hitching rides for the few times I head out.

If anyone is interested in buying it, email me at beljoeor[at]gmail[dot]com. I’ll deliver anywhere in New England and most of New York for no extra cost.
trail riding · trailering

Fall Trail Ride at Groton State Forest

First things first: as I alluded to yesterday, late on Saturday, I started getting a niggling worry about my original Sunday plans to bring Tristan down to the GMHA Fall Foliage Ride. I mean, I always worry, and last week was not exactly ideal preparation, but now I had some concrete reasons.

(Second things: in an attempt to break up the wordiness of this, I’ll insert pictures throughout the text.)

In a nutshell, even the staid, conservative, reliable weather sources were predicting record-breaking high temperatures, up even into the mid-80s. Tristan has more than half of his winter coat grown in already, has not been drinking great this week (though I added in electrolytes and soaked beet pulp to help counteract this) and the really unknown factor: Cushings affects a horse’s ability to regulate its own body temperature. We already knew that Tristan did not cope well with an unseasonable cold snap; how would he do with an unseasonable high? GMHA would be 8.5 miles of terrain about 1.5 hours south of where we lived, so potentially even hotter, with more exertion. (Yes, I know those of you who do 10 miles on a light day are laughing at me right now…sorry!)

I started texting the friend who was planning on going with me, and she responded immediately saying she’d had the same concerns. She also has an older, not in full work horse with a solid start on his winter coat. WHEW. I headed to the barn Saturday night to prep the trailer with everything jumbled in my head, and then talked to the trainer’s barn manager/assistant trainer, M. I laid out the facts and she knew instantly why I was concerned. A few minutes of conversation and she said in our place, she’d fall back on plan B.

Plan B: Groton State Forest. Run by the VT State Parks people, it’s a massive, MASSIVE preserved tract of land – big enough to have seven different state parks within its borders. It’s 26,000 acres, and according to the state park website, the second largest contiguous land holding in the state of Vermont. It’s also about 25 minutes away from the barn, and I’d heard the name tossed about a few times by people when they discussed good places to trail ride around here.

I texted my friend back, and as she pointed out, M. is always right. We scratched from GMHA (even when my horse is healthy, I always seem to be losing money on entries…HORSES…) and re-oriented for Groton. We planned on leaving the same time so as to get the horses home before the heat really hit. I prepped the trailer and looked at the trail map when I got home.

The next morning, after an 80 hour workweek, I got up at 5am and walked the puppy, then headed to the barn. The fog was absolutely unreal – no more than 20 feet visibility. I missed a turn I take every day, sometimes twice a day! Then, when I stopped at the top of the hill to hitch up the trailer, the truck’s wheels slipped and slid in the dewy grass. I backed up and turned and wriggled out of the field, but not without digging the grass up a little bit and then getting myself pointed the wrong way out the field, which necessitated three-pointing the entire rig in some stranger’s driveway so I could get pointed back toward the barn. At 6:30 am. Good thing I’m a confident trailer driver?

We got everything loaded, then loaded both horses. Tris was his usual self, but got on in a minute or two. It was chilly – low 50s – and my trailer gets a lot of air flow, so I put his new Smartpak cooler on for the ride. Then we set out for an extremely pleasant drive: little traffic, all local roads, and once we got back out to the main road from the farm (about 5 minutes) only one turn.

We pulled first into New Discovery State Park, because from our online research it looked like the biggest and most accessible, and therefore the most likely to have plenty of trailer parking. HA. NOPE. It was entirely narrow dirt roads that led to campsites, and the park office wasn’t yet open. (There was a sign saying, “Pick a site and come back after 9am.” Hmmmmmm. Not helpful.) So I three pointed for the second time that morning, and headed back out. We parked by the park office and jumped out to see if there were any maps or any better indications of parking lots at other sites in the state forest. We discovered that while we could in fact park the trailer in a camping spot – and there were some specific horse camping spots – we were both kind of meh on the trails we saw out of the campground, so we moved on.

We settled on Kettle Pond State Park, a few miles down the road, because it looked like it had both a decent parking lot and access to the rail trail through the park that was a piece of the Cross Vermont Trail. Back down the road we went, and about 2 miles later I pulled over and we were right! Though the parking lot was not huge, it was plenty big enough to pull the rig over into the shade, and a short hack back along the (not-busy) road a few hundred feet would put us right on the rail trail.

We pulled the horses off, and Tris was his usual self in a new place: dancing and pacing a bit but nothing seriously bad. I had parked the rig in such a way that meant I couldn’t tie him on my side (whoops) but I rarely tie him anyway when we’re out, unless we’re going to stand for a while. I folded his cooler and put on his saddle, and then left the cooler over his saddle while bridling, just to be extra-cautious. He seemed not too warm at all under the cooler, which was exactly my hope. The only bad moment: Tris stomped on my foot HARD while dancing around, and I was wearing sneakers. We had a spirited conversation, and he regretted it, but wow, my foot hurt like a bitch.

(One other small aside: when I pulled off Tristan’s fly mask – I hauled him with it to keep protecting that funky eye – he had some kind of charming pussy scab on his cheek that looked like a bug bite. He wasn’t terribly bothered by it, so I wasn’t either, and back at the barn later that day I cleaned it up and slathered it with Corona; I think it was a small initial bug bite that he rubbed through the fly mask and made quite a bit more irritated. Idiot.)

We mounted up and set off. Our stated goal was to do nothing more than expose them to a new place and see beautiful foliage, and I have to say, though I know H. decently well after seeing her around the barn and hacking out in the fields there, I was thrilled with how well we both communicated and were on the same page that day.

There’s not too much to report about the trail, other than WOW. Tristan was eager and happy and gave me an absolutely beautiful forward walk on the buckle for nearly the entire ride, until the last mile or so when he was clearly getting tired. We ended up doing about four and a half miles in an hour and a half, on footing that was quite good – not good enough to gallop, but easily good for trotting, especially if a horse were booted. We walked only, and turned around when the horses first indicated they were a little tired.

And I just have to say: I have lived in the northeast my entire life, and have now lived in 8 Vermont falls, and I have never – NEVER – seen foliage like this. It was unreal, almost painful to look at the colors were so riotous. The pictures don’t even capture a quarter of intensity of it. We could not stop talking about how amazing it was, and we’re both pretty jaded about foliage!

Tristan was a little warm and a little sweaty when we got back to the trailer, but nothing terribly serious. I had brought an irish knit with me, and stripped his saddle immediately, then threw the knit on and rubbed his back and chest with it a bit to rough up the winter fur. He was cool and mostly dry by the time I put him back on the trailer without a sheet. He spurned water, of course, but was happy to attack the hay on the trailer and seemed in great spirits.

We got back to the barn without incident, and both horses looked and felt great off the trailer. We tossed them into the dry lot paddocks with the extra hay from the hay net and they both had good long rolls and stood in the shade. By this time, the heat was really cranking up, and I was hot and exhausted and the foot that Tristan had stepped on was finally starting to throb.

We cleaned out the trailer, hauled everything inside, and hit the only major snag of the day: the trailer ramp would not close. What the HELL? Problem: the mat on the trailer ramp has to slide snugly inside the wall of the trailer, and it was catching, bumping against the left-hand side of the trailer. Which made zero sense. I heaved, slammed it, cussed, and finally examined the entire thing inch by inch and discovered the problem.

The ramp was connected to the trailer itself by three large hinges. Somehow, when we took the ramp down and/or when the horses came off. the ramp shifted less than 1/4″ on the hinges. I could see the bare, unpainted part of the hinges exposed to metal underneath. Somehow, we needed to shift the (incredibly heavy, not spring-loaded, all-steel) ramp back 1/4″ to the right so that it would line up again with the trailer. Cue a hunt for WD-40 through two tack rooms, an equipment room, and a garage. We lubricated the hinges and the ramp would not budge.

Finally, I looked around and realized that the way the hill up and out of the barn turned, it would mean the trailer would tip to the right, and gravity would be on our side. I inched the rig up, and put it a foot or so off the road so the right wheels of the trailer were off-road and the whole thing was substantially tipped – not so much that it would’ve rolled, but definitely diagonal. We then lifted the ramp halfway and rocked and rocked and rocked – AND IT WORKED!

Just at the moment it slid in and we latched the door, the trainer came running out of the barn to warn us that if we drove into the drainage ditch we would ruin some carefully constructed rainwater draining systems. EEK. I swore we were not really in the ditch (we weren’t) and promised to back it out precisely the way I’d gone in, which I then did, inch by inch. WHEW.

I parked the trailer, drove back to the barn, and fed Tristan some beet pulp with electrolytes, watched as he took a big long drink, and then headed home and proceeded not to move for several hours while I watched The Roosevelts and crocheted.

nutrition · trailering

Feeding Beet Pulp

Tristan has not been drinking as much as I would like lately, and with plans to take him on the road on Sunday, I wanted some extra tricks up my sleeve. I’ll incorporate electrolytes into his feeding plan over the next few days, but wanted something to give him on Sunday while we’re away.

Enter beet pulp. Beet pulp is basically the shreds of what’s left over after all the sugar has been processed out of beets. Sounds delicious, right? It’s actually nutritious (for horses, anyway) and most importantly low in starch. Dr. Kellon, a leading expert on Cushings nutrition, suggests it as great safe calories. While it can actually be fed dry (another old wives’ tale bites the dust), it also absorbs a TON of water – which makes it ideal for my purposes.

I bought 35lb of beet pulp for about $13 at my local feed store (literally right off Main Street of the state capital, oh Vermont, never change), making it also pretty inexpensive. Whoo! I queried the collective wisdom of COTH to see if I could feed it intermittently, and the answer was a strong affirmative. (Let me hasten to add that COTH is not my one-stop-shop for veterinary answers, but for straightforward practical questions, they are great. When the answers all come back “yup, no problem, go ahead” I feel on safe ground.)

To be extra cautious, I am giving him a few handfuls per day in the days leading up to the ride to get his gut used to the beet pulp again. (He has eaten it in the past at other barns with no problem.)

So tonight, after puppy class, I went out to give him his first bit of beet pulp. I mixed two heaping handfuls of dry shredded beet pulp with about 2Q of water.

Dry, before adding water.
After adding water.
Then I set my timer for 15 minutes and proceeded to wander around. I didn’t want to start on any cleaning projects because I quite foolishly had not changed into jeans after work and didn’t want to completely destroy my work pants. I petted Tristan on the nose (he was BUSY with his HAY, MOM), and wandered around outside.
My pretty new car, posing in front of the dry lot paddocks, with foliage backdrop.
I checked on the water level in Tristan’s paddock: pretty good. (Not low enough to make me haul more out in my work pants…)

Then I turned around and the barn was pretty.
I brought the beet pulp out so it could enjoy the view. This is halfway through soaking.
Done! This is especially soupy beet pulp, but I was still amazed at how much water it soaked up.
A+ pony approved!
Tristan ate the beet pulp up beautifully, even slurping the extra water. Victory! (For now, says the pessimistic side of me.)
He’ll get a few more handfuls Friday & Saturday night, and then half a bucket of dry + full bucket of water on Sunday at lunch. Every little bit of extra water I can get into him helps.

Trailer Loading Practice

A barn friend and I are planning on hauling out to the GMHA Fall Foliage Ride this weekend. The last time Tristan got on a trailer was for his surgery, and the barn friend is leasing a new horse and had never seen him load. So I brought my truck out to the barn, hitched up the trailer, and we worked on loading with both of them.

Tristan is not great at loading. Over the years, he’s gotten much less dramatic, thankfully. Yesterday, he approached and backed off 3-4 times before finally walking on. I tend to take a very patient road with him and let him look as much as he wants. I never ask him to go forward until I see that he has softened a little bit. He only gets punished if he goes back, and then he gets shanked once or twice, hard, with the chain. Experience has taught me that if he gets away with backing up he will go from minor nuisance to full-blown dangerous in minutes, so I do not tolerate a single step back. Each of the times he “backed off” yesterday were him squirreling out to the side, and my choosing to turn and re-present rather than argue about lateral work. He only yanked back once, and regretted it.
Pawing, pawing, pawing…
We left them to settle in for just a few minutes, and I fed Tristan some treats. When I stepped away for a minute he commenced pawing, which is par for the course for him. When we’ve actually gone somewhere, he usually just chills once we’re there. God forbid, however, I load him to leave and then don’t pull away immediately. WHAM, WHAM, WHAM. I have done everything over the years to stop it and nothing has ever worked. Pawing is his annoyance behavior of first resort, whether he’s in a stall, in the wash rack, or on a trailer. It’s just part of him.
He backed off the trailer beautifully, again according to pattern: one hasty backup into the butt bar as soon as he hears me back there, I jab him in the but with a knuckle, and he steps up. Once I’m sure he’s settled, I drop the butt bar and pull on his tail and tell him “back.” He backs delicately down the ramp in mincing, careful steps, leaving me plenty of time to grab the lead rope I leave tossed over his neck.
I need to make a few purchases to update the first aid kit – instant ice bag and electrolyte paste, primarily – but other than that we should be good to go on Sunday!
first aid · trailering

First Aid Kit for the Trailer: Spring Checkup

Okay, so it’s more like midsummer checkup, but still: yesterday, I went through the first aid kit that I keep in the trailer. It’s a fairly obsessive kit, because my theory is that while I’m at the barn, I can find just about anything I need or run out to buy it posthaste. If I’m out on the road, who knows where I might be or what I might find?

I keep it in this tupperware box, which is about 12″x9″ – pretty decent size. It’s not packed to the gills. First up was going through the checklist that lives with the kit itself.

Sadly, because I’m a loser, this checklist is left over from the last time I went through the kit, and is no longer accurate. So I just checked again and made additional notes.

Missing this time: two rolls of vetwrap, the lube, the 60cc syringe, the scissors from the suture kit (huh?), the tube of banamine, one of the two pens, one of the two bags of electrolytes.

The antibiotic ointment had expired, as had the saline solution. I threw away the antibiotic ointment but saline solution doesn’t really expire, thanks marketing guys.

I tested the flashlight batteries and the in in the pen, then the thermometer – I stuck it into my armpit. I once nailed some Pony Clubbers on their horse management inspection because while they had a digital thermometer, the batteries were dead. Since then, I’ve been very careful about checking my own during these inspections, because: karma.

Some things I decided not to replace: the second pen, the second roll of tape, the scissors, and the second dose of electrolytes.

Some things I replaced right away: I had already replaced the banamine and just kept it in my main tack trunk, so I transferred that over to the kit. I have enough leftover vet wrap to cover my entire horse head to tail, so it was easy to grab two rolls out and get them to the kit.

I stopped by Walmart on the way home and bought more lube (which necessitated a fair bit of considering time in front of the personal pleasure section at Walmart while wearing my breeches, earning me more than a few sideways looks), a tube of antibiotic ointment, and one addition to the kit: a travel size tube of antibacterial hand wash.

I am not a big believer in the stuff on a daily basis, but I’ve seen how effective it can be around the barn for biosecurity. Every new horse gets a quarantine stall and a big pump jug of the stuff on the door. Our barn is an interesting confluence of several circumstances – rural area with a few other not-great barns nearby, super-fancy and $$$ horses in for training or sales all the time, one or two pregnant mares or new babies at all times, and a very particular ban manager. It’s really great, but it does mean there’s a higher level of care taken about that sort of thing.

Today, I stopped by Tractor Supply and picked up another 60cc syringe with catheter tip. Pre-surgery, I had a half dozen of these around; during Tristan’s rehab, one after another succumbed to broken parts, staining from betadine, or just plain old got lost. Time to re-up.

All I have left to do is update the inventory list and the emergency contact information inside (new barn, need to add the fiance since he would probably care if something terrible happened).

Always bring peppermints!

blog hop · trailering

Viva Carlos Blog Hop: Travel Bug

I’m catching up, ok?

Most of us have been somewhere with our horse, whether its camping, a trail ride, a horse show or just moving them to another barn. Like most things with horses, sometimes success is just a measure of trial and error. What is your best tip for traveling with horses?

Lots of other people have answered to make a list and check it twice. I do that. I even have a separate sub-list for my trailer-specific first aid kit. To describe it as obsessive would not be doing it justice.
However, here is my absolute #1 tip for travelling with horses: bring way, way more water than you think you will need, and bring it from home.
There are many reasons for this, so I’ll break it down.
First, horses can become suddenly picky in the weirdest of ways. Having water that they’re used to, from home, diminishes the chances that they’ll go off drinking.
Second, never, ever, ever plan on water being available where you’re going, even at shows. Biosecurity is a real thing. If you arrive at a show, and the only way to get water is out of a communal trough, DO NOT USE IT. Don’t be that horrible example who brings strangles back to your home barn. (I am also fairly neurotic about not letting Tristan graze if trailer parking is in a strange pasture, but I know that’s a little above and beyond.) Bringing your own water helps neatly avoid this problem. If there’s a hose/spigot available, and you can fill up separately from the main trough that everyone and their cousin has used for their horse, then that’s a bonus, and fill up your empty containers before you go home, just in case.
Corollary to this: don’t be that person who waltzes up to the big trough and lets their horse drink right out of it. You are the Pony Club poster child for thoughtless horse owner. I’m serious about this. Don’t do it. If you must, dunk a clean bucket in to fill up.
Third, you never know how long you’re going to be stuck on a trailer. “Oh, it was only a short ride to the trailhead!” becomes a 4 hour wait in bumper-to-bumper traffic on a hot summer day. If you didn’t bring enough water, or didn’t fill all your empty buckets from the (safe!) hose before you left, then you can’t pull over and offer your horse water and you are going to really, really regret your lack of preparation. I’ve been hauling horses at the tail end of what was supposed to be a short drive and sat for hours and hours in stopped traffic when a horrible accident closed the entire highway. I was very glad I could have my companion jump out and offer water to the horses.
I never hitch up the trailer without somewhere between 20 and 40 gallons of water, depending on how many horses I’m hauling. I usually fill up four 5 gallon buckets, and then I have a few 5 gallon gas containers that I fill up with water as well. I dump and refill them regularly if I haven’t used them up. I scrub them and let them dry in the sun if they show the slightest hint of slime. (I also have 3-5 possible buckets to use for sponging or drinking for horses, so they’re not drinking out of those buckets.) I covet one of those big water tanks that tucks under a gooseneck or in a tack room. Someday!
If you’re hauling with someone else who doesn’t have adequate water buckets in their rig, then it’s your responsibility to provide water for your horse and, if you’re a thoughtful person, for the other horse as well.
So, there’s my lecture/advice. Water: don’t leave home without it.