I was adding about an 1/8th cup of canola oil, twice daily, to everyone's diet because it is high in Omega-3. Other oils are high in Omega-6, which is thought to aggravate inflammation. "Was"
is the operative here. I had been using canola oil for about a year.
My horses come in at night & out in the morning. One night I noticed my 20 yo & 22 yo were not urinating as heavily as they should be. I sort of wondered if the oil was having that effect on them, but thought that was stupid and kept using it.
Then I ended up on crutches for awhile and Mr. WTW had to feed the horses for a couple weeks. To keep things a little easier I said "forget the oil".
By the time I was able to get back to feeding everyone, I noticed those two senior horses were back to peeing normally (that means half a river).
It could just be coincidence and the canola oil really wasn't inhibiting the older horses' ability to pee, but I'm not putting them back on to find out.
The best and safest thing to add for weight gain would be rice bran. It comes in pellet or powder form. It is 20% health
I suggest rice bran because I am reading about a lot of choke cases with beet pulp. It doesn't seem to matter if it is soaked or not. The one thing all these choke victims do seem to have in common is that they are fast eaters and gulp their food down.
I won't feed beet pulp as I feel the rice bran is much less of a worry issue. My I-R/EMS horse lost about 80# in six weeks when he first got noticeably sick. I have been feeding him 8 measured ounces twice daily for two years and he is maintaining his weight on that small amount
Point-being a small amount of rice bran might be able to be added as a weight-gain supplement to your horse's diet
Pelleted rice bran, a pelleted vit/min supplement, and Omega-3 Horseshine are all my four horses get since the one became insulin resistant.
The I-R horse does get a host of additional herbs & minerals geared toward controlling his glucose level.
Hope this helps