Hi Suzanne,
I am not sure if it is totally a management issue or not as sometimes it just seems to happen out of the blue on the rare occassion and nothing has changed and one never finds out why it happened. I have had horses for over 25 years, and lost my first to colic this year, but have not really changed any of my ways in the 25 years. I rarely have colic issues (4 cases total in the past 24 years not counting the foal last year that had colic issues and numerous other physical issues that were causing colic), but this year I have had 3 in 40 days which tells me that something is/was seriously wrong... Now with that said, there are some things that I have learned, especially about minis...
First is that I have had more issues with colic in minis that with the large horses. It just seems that minis are picky in this way. I have had minis for only 10 years, yet my colic cases have been split 50/50 between minis and full sized horses until the ones that happened this year. The ones from this year were definately a management issue and it will be a very long time until I forgive myself for feeding that course hay from our field that resulted in the death of our precious yearling. (I can here Kim_Rule yell at me now...) I wouldn't have bought that hay, yet I thought that it wasn't that bad and since we grew it that I would use it. Trying to pinch a few pennies has resulted in a huge cost... I will never feed anything that I wouldn't be willing to buy from now on. Big lesson learned!
I rotate dewormers like you do and deworm every 8 weeks. Some have found that a daily dewormer will help decrease colic if the worms are causing it. Have a fecal count done on the manure from the colic case and that will tell you if that is part of the issue. I have only seen one colic case from worms, and that was when we bought our first horse as a 2 year old and dewromed her the first time. This was 25 years ago. We didn't know she was loaded with worms and the dying of those worms caused an issue. She never coliced again after that one episode. We had her until she passed away at the age of 18.
I add salt to the food. It does cut way down on their colic from not drinking enough. I was told to add a teaspoon of loose salt to the grain of my most recent case and to wet that food. It is pelleted, so the food absorbs the water and the salt sticks to it. All of my minis are now getting 1/2 of a teaspoon added to their grain again. (I stopped this practice when we moved the farm as I don't have individual stalls to feed in. Now it is back to standing guard over the grain pans to ensure that the horses all get their share of extra salt. When we were feeding salt regularly, colic issues didn't really seem to occure.)
I feed whole flax seed every day. I don't soak it or anything. Just top dress my grain with it. This has been VERY effective on keeping my horses free of sand when I do it regularly. The 3 that coliced this year were free of sand when checked for it which included ultrasounding them.
Hay... Again, This is where I have learned a HUGE lesson... Make sure that your hay is nice and tender. Not course like straw. It will cause impactions if it is course. I have changed my hay and hopefully my colic cases go away now. Another thing about hay... If you feed hay part of the time and turn the horses out to graze part of the time, it can cause the horses to not want to drink enough. The reason is that the horses are less thirsty when they graze due to the higher water content in the green grass. At least that is what the theory is. Anyway, our two cases in the last 2 weeks which were extremely bad and resulted in our only loss from colic were from horses that got limited grazing on grass. Our boys were turned out for a couple of hours each night for their evening meal. Funny thing is that minis are the only horses I have ever limited grazing on, and well, my full sized horses always had free choice grazing and never coliced. So I am inclined to think there may be some truth to this theory.
Beet pulp. I am not familiar with it, but it may become a huge part of my routine if I can find a way to incorporate it into the daily chores. The biggest issue for me is that I don't live on the farm, and my farm partner is reluctant to take on additional tasks as she is overwhelmed with caring for the horses and her in-law and working full time, not to mention her health issues. I will have to see where this will lead on this one. If the horses were at my place, I would certainly be trying this one out. Still, in all my years with horses I have never used beet pulp and never had an issue with colic to speak of until this year.
And finally, the weather here is playing a big part with the horses. As you know, it has been really hot one day, and cool the next. I think it has been a weird summer here, and I have noticed that the last two cases of colic were following a sharp cool-down. The vets that I have talked with told me that right now we are in the peak time for colic related to the extremes in temps and the fact that the days which are in the 90's also have nights in the upper 50's to low 60's. I am thinking that they are not drinking enough due to the cool weather and this has been an issue. Again my vets recommended making sure that the horses not only have free access to salt, but that you make sure to add salt to their food to increase the thirst the horse has. This was heavily stressed.
Along the same lines as the weather, make sure you have tank heaters for your water in the winter. I have found that my horses will easily drink double the amount of water in the cold winter months when the water has the tank heater in it to keep ice from forming on it. It really is amazing that even though we break the ice and remove it that the horses don't drink that cold water like they do with the water that is kept just warm enough to keep ice from forming.
Hang in there and keep trying things until you find what works best for your horses. And like you, I am also one who constantly looks out for what I can do to prevent colic as that is one of my biggest fears concerning horses.