I can give you information from this current year, not speaking to external rotations.
Is there a max hours limit for rotations? In the VTH or elsewhere?
There is not a hard-set limit, no. Most departments recognize the SAVMA guidelines and generally do look out for your wellness. For example, if you have to stay really late one day, there is a good chance they will allow you to come late the next day.
Mandatory time between shifts?
Not currently in place.
How much on call is typically required? See below
Do you get breaks? How many per shift and how long are they?
There aren't set breaks. This doesn't mean you don't get breaks. YOU have to dictate your own breaks. If it is late afternoon and you haven't had lunch you have to let people know and get help so you can get something to eat. I always am planning ahead - if my first appointment is at 11am, I eat before the appointment because I know I'll be in diagnostics for a while. If you aren't actively seeing a patient you can generally just go do your own thing, and this can be for *hours*. I've never seen it be an issue with people having to leave in the middle for a doctor's appointment or something just as long as you communicate really well.
Day start: Starts at 7am for most hospital rotations with patient care. Earlier for rotations with intensive patient care (can be different on a day-to-day basis) which may include soft tissue surgery, equine surgery, and neurology. Certain hospital rotations (community practice, oncology, cardiology) you are less likely to have patient care but it is still possible. I have oncology on there but they very commonly have patients to care for, just they are usually not hospitalized so you don't even need to get there until closer to like 7:45. If you have no patient care (radiology, anesthesia) it starts at 8. ICU varies (you work a week of each day, swing, and overnights).
Day end: So variable!!! The latest I've stayed on a regular work day was around 8pm a single day on neuro. For ME, it has been rare I've left ever later than 7pm. Average is probably 6pm. There was someone from one of my rotations that had to stay until 12am one night to do a blood transfusion when everyone else was out by 6pm, so unfortunately it is very luck of the draw.
On-Call: You have the potential to be on-call for ICU any day of the week while on a small animal rotation in the hospital (excluding ICU, anesthesia, surgery). I don't know how many on-call shifts I've had in the year (I'm just going to guess 12) but I was never actually called in on one of these. Someone in my class was on-call 48 hours in a row over a holiday weekend (and I honestly don't understand how this could've happened because the shifts are only 8 hours) and had to be at the hospital for 36 of those 48 hours. You have 2-3 on-call shifts while you're on anesthesia. You have 1-2 on-call shifts on both SA SX rotations. You have 1-2 on-call shifts for neuro. I was only ever called in for anesthesia. I had a long surgery (from 5pm-11pm) and was allowed to come in late the next day (10am), and when I was called in the next shift at 5am I was allowed to leave early.
Weekend duty: Weekend duty is extremely common. Most times patient care runs 7-8am. You'll have to stay longer if you got an intensive transfer, or have a discharge over the weekend. I knew of one unfortunate internal medicine transfer team that got stuck there for 14 hours one Saturday doing blood transfusions. That was a freak weekend, it is not a normal occurrence. Weekend care can get divided up differently where you might have one weekend off for rotation and work the other, or split it up Saturday/Sunday instead. On barn rotations you can have primary care weekend duty (at the barn 8-5, whether or not doing treatments) or back-up (on-call) based on a lottery.
Overnights: You have one week of small animal overnights; these shifts currently run 9pm-8am. You have two weeks of large animal overnights. These are split with a swing shift (5pm-12am for one week, 12am-7am for one week) Unfortunately, this later shift does have to show up at 5pm for rounds and is only dismissed after rounds (around 6:30pm) if is quiet enough, and they remain on-call until their shift starts. So, there is a possibility to have to be in the barn from 5pm-7am.
Extra-special rotations: For ultimate work-life balance, enjoy the odd schedule of Clin Path (1 week elective), Necropsy (2 week core), Small Ruminants (2 week ag choice), and Anesthesia (3 week core). These are special rotations that have irregular hours. For example, in necropsy your day usually runs 1-5pm. In Small Ruminants 8am-12pm (depending on season). Anesthesia, runs 8am-5pm but you can go home if you do not have a case, or once you finish your case.