Hmm... New pasture = New feed?

Right now my horses are on dry lot with 24/7 access to a round bale and get grain 2x daily (high fat/low starch for their drafty-ness)... They only get 1lb/feeding each and are, well, round... Next week we are moving and will have pasture. Obviously I will be introducing them to it very slowly. Once they have been introduced to pasture, it will be for about 8-10 hours a day, then they will be in the paddack at night with hay. (The pasture is across the street with no shelter and I just don't feel comfortable keeping them over there at night) Obviously their nutritional needs are going to change. I was thinking about either switching to a ration balancer or finding a forage based feed to give them instead of hard grain... What are some ideas? What do you do? I just want to make sure they can keep getting their oil and if necassary an added supplement. They will also have 24/7 access to a salt/mineral block and water.

Oil.. Like canola oil? Why do you want to feed oil if your horses are round? DrumRunner posted a great article about oils
Adding Oils to Your Horse's Feed.
Oils gain weight on horses due to all the fat, and I don't get why you would need to make sure your horses get their oil if they are chubby? Horses really don't need grain or oil, or anything else when they are fat besides their roughage (assuming it has all the appropriate vitamins and minerals, if it doesn't ration balancers are great). They only need grain or anything fatty if they have trouble maintaining weight, need to gain weight, or need more energy for their type of work.. If the pasture is high quality you don't need to feed ration balancers, its a good idea to get it tested to see if it is deficient in anything. You can also consult your local vet for any minerals that your area may be deficient in (most of US doesn't have enough selenium). Good luck!

I have draft horses. They are prone to EPSM and cannot utilize starches and sugars so to give them an energy source, oil is added to the diet. They are also more prone to laminitis and founder caused by starch/sugars. They require a high fat/lowstarch&sugar diet. I wouldn't expect someone who doesn't own or understand draft horses to know that, so I should have mentioned it in my original post. We do supplement selenium because Maine is selenium deficient.

I should also mention that the EPSM diet is also reccomended by the vet.

Ah, did not know that about EPSM in draft horses!

Yeah, it sucks haha. I think the QH community calls it PSSM... I can't even feed him feeds that have molasses... A low starch/high fat pellet is best, mixed with his oil, or I can do beet pulp/oil/supplement or alfalfa/oil/supplement... I just have to find the right combination for his enviroment and workload, which is pasture ornament for another 6 months to a year.