Like many have said already we try to keep foot trimming to a minimum and now tend only to do it in response to a problem. When we first started with sheep a few years ago my father in law, (a long time sheep and goat keeper) instructed us to trim the feet every 6 weeks to minimise the risk of pockets forming in the hoof that could collect mud and infection. Being an obedient son in law I did as I was told. That first summer I'm sure our sheep's feet could have won prizes in a sheep's feet beauty contest. And they were constantly lame.
Every time you trim away the hardened hoof and expose softer, less resilient tissue it leaves the feet more tender- it is also very difficult to manicure feet well without drawing blood or at least getting very close to where the vessels are, increasing the risk of infection. Years ago I was a keen long distance runner- a golden rule of running is not to cut your toenails in the week prior to a marathon to avoid getting sore toes- actually that made more sense in my head !
Since we stopped trimming routinely our incidences of lameness are massively reduced. When its wet the problems are more frequent, the hoof tends to bend creating pockets for mud to collect, rather than snap off neatly as it does in drier times- but a lot of the time even if a sheep is limping for a day or two, it can resolve itself without resorting to trimming and spray. if after a few days its clearly not improving then we will gather them in and sort it. this lovely hot dry summer left our sheep with beautifully crafted feet and we hadn't touched their hooves since lambing in April.
the other factor that I like to think makes a difference is the understanding of the role various trace elements play in livestock health, and in this case in feet health. foremost amongst these when it comes to hoof hardness is Zinc which is crucial in the formation of keratin, the main structural protein in hoof ( and wool) formation. other elements such as copper, manganese and molybdenum play a role too. As a result I always ensure that the sheep have access to mineral supplements ( licks or buckets) as I am not convinced that our low input pastures will automatically contain all they need. Obviously sheep are extremely sensitive to too much copper (though they do need some) so I only use licks or buckets that are sheep specific.
every time my father in law visits I have to practically wrestle him to stop him attacking the sheep's hooves but it feels we have found a way that works for us, though we are unlikely to win prizes for their beauty.