So, for my 17hh Warmblood working 5 days per week and hunting 1 day, the following seems to be keeping the condition ON:
1) 900 grams micronised linseed meal split in to two feeds;
2) 800 grams (dry weight) speedi beat split in to two feeds;
3) Saracen Stamm 30 Balancer - 1 kilo split in to two feeds;
4) 10 grams table salt per day;
5) Ad-lib Haylage;
If you could fit in three feeds per day, this would also really be of benefit and you could slightly increase the overall amounts above then split across three feeds.
Hope this helps!!