My Shetland has had lammi the last 2 winters with no change in diet, hes fine on restricted grazing during summer with no muzzle and has unsoaked hay and has Happy hoof at the same rate all year round, his lammi appears to be triggered by mobility issues, stress/concussion (not totally discounted frost but hes out on it now and so far so good so hopefully will be able to), after his first attack I put him on a liquid supplement, then took him off it, last winter he had another attack and I put him on lami prone, he has been fine upto now on it - schools of thought as to wether it actually does anything suppose the only way I am going to know is to either a. take him off it and see if gets another episode or b. leave him on it and hope he doesn't, so going with the latter this year.
I feed happy hoof at maintenance dose all year round which for my little man 150kg is 1/4 scoop morning and night - so not exactly bulk feeding. we put our other two natives on HH, our Sec A gets a third of a scoop morning and night and our 13.2 PB gets 1 scoop morning and night, and they have all maintained a consistant weight on this, PB at 19 does get Alfa A oil in winter as she has a tendancy to drop weight over winter as she is getting older.Other than that even at -17 they get a flap of hay each morning and night and dig for the rest if snow/ice on the ground- otherwise they will get no hay as we have plenty of grass on the fields.
Lammi is not always to do with diet in so far as what is being fed ,there are so many triggers but generally even then it is the imblances resulting in the gut which seems to be the key, I would rather feed the supplement in the hope that it will prevent than do nothing ..
in our case if stress related then this will be due to related imbalance in the gut which hopefully the suppliment will help counteract -
Unless he has had a lammi episode in the past there is nothing to say that because he is a Shetland Type rather than another breed he is lammi-prone, they all are if allowed to be obese, but if you have their weight managed then hay and a balancer over winter should be enough, if obese then a balancer and if out 24/7 even on minimum grazing unless hard frost on ground let him work for it and give token hay only if necessary, if part stabled then the only thing I would say is make sure get as much turn out as possible - exercise and keeping moving is certainly a big part of our lammi experiences.