Hmm. Depends a lot on the breed as well as the environment. What were they dying of? You need to know to be able to tackle it.
What were the symptoms?
Everything means something, even if it doesn't seem to. Turkey 101 depends on what breed you have, so for heavy production commercial meat breeds it's different than for heritage breeds or random mongrels...
I can only offer advice on mongrels. I had mongrels made up of some black-eyed-whites, bourbons, buffs, blacks, and some incredibly inbred ancient heritage line. No heavy duty producers like broad-breasted commercial ones, not that mine were very narrow but they weren't total meat breeds either. Some of mine had some bantam genetics from the terribly inbred line. Actually most lines I was able to get were terribly inbred, some people thought inbreeding "didn't matter with birds". :/
But here are some basics I found, some of them found out the hard way:
They are mostly green feeders. Their livers are weaker than chickens' on average. The majority of all poultry deaths are due to digestive diseases, specifically those involving the liver, so take care of their livers as much as possible, and almost all health problems are eliminated as the liver takes care of the whole body.
So, raw dandelion, milkthistle, raw onion and garlic, some herbs and spices etc are all good foods for supporting livers... But fresh green grass, available for them to pick for themselves daily, as the bulk of their diet, will help their health so much it's incomparable to caged birds' health. Greens have chlorophyll which acts as a constant gentle detox. Whether you keep animals for pets, eggs, or meat, letting them get to forage will give them so much more health and their products so much cleaner and better a flavor, it's just about the only way to go --- if you're able to, that is. Some of us have to make do with cages, though. Even then supplying fresh greens is doable and highly recommendable.
Turkeys are preferably more vegetarian than meat eaters unlike chickens which do better with meat in their diets. This doesn't apply to specific breeds like meat breeds which need more protein and may have adapted to a meat based diet like intensive production chicken breeds which were developed in conjunction with a specific diet and don't do as well on most other diets. So for a vegetarian source of protein, millet seeds are great.
They are good with some animal proteins, like insects and eggs up to a point, but bear in mind that heart and cardiovascular diseases are quite common among poultry and other domestic species, and this is in large part because we tend to feed them the exact same diet we know to avoid as a staple in order to avoid heart disease in ourselves. Avoid having cooked oils and proteins as the staple diet if you want to avoid most diseases caused by them, but, it will take some research into avoiding it and using alternatives. If you keep your birds for your own health then this is obviously pretty vital, to make a pun out of it. Their health or sickness is ours as well.
To prevent deaths to Tuberculosis, I fed them hard boiled eggs with raw dandelion or raw onion for their first few weeks. They will let you know when they don't need it anymore.
To prevent deaths to Blackhead I only treat those that were so weak as to fail to overcome it themselves. I would wait until their poop was bright yellow and liquid, at which point they were voluntarily fasting, and I'd give them a cup of raw cow's milk which had had a teaspoon of honey mixed in and then had been allowed to sit for at least an hour. I'd scrape the fat off the top and give it to them and it'd fix up over 90% of them within 24 hours and their immunity to BH was lifelong. Breeding on strong ones led to, after a few generations, BH immune birds.
Since BH attacks the liver it's best to take them off grains and keep their diet as clean and alkaline as possible... Generally speaking, millet seeds and whole rolled oats are good at that point, and as much fresh green grass as they want, but avoid pellets, cooked foods, and animal proteins asides from that initial bit of raw milk. I would not use cooked/pasteurized milk, or homogenized milk, because cooked proteins and fats and homogenized milks are exactly what the liver does not need at that point and could kill the bird. Since goat's milk is naturally homogenized I suspect it may not work like cow's milk, but I don't know for sure.
I soaked all their grains overnight and basically just let the turkeys choose from among the same feeds the chooks got... So they'd have soaked grains and seeds, with freshly minced raw garlic more often than not, and all manner of spices from cayenne to black pepper to curry.
Raw garlic is very potent. It's a powerful natural antibiotic which doesn't harm their probiotic microorganisms, in fact it's a prebiotic as well and feeds them, or at least it feeds the beneficial ones. It has been used in hospitals to treat bacteria that are resistant or immune to the strongest artificial antibiotics.
It's high in sulfur, which builds up in their flesh and controls internal and external parasites after a while of them eating it regularly, as a bird can tolerate thousands of times the level that is fatal to a parasite. Sulfur is also anti-disease and aids in rapid healing. Raw garlic has over 34 antibiotic compounds but the strongest is Allicin which forms in response to damage to the cloves, and dissipates in a few hours or days, so fresh and raw is best, but any form of garlic will help. It's antiviral, antibiotic, antimicrobial, antifungal, antibacterial, anticatarrhal, and basically anti everything unhealthy. Going to the extra little bit of effort to give my birds raw garlic regularly saved me a couple of worlds of trouble many people simply take for granted as being inevitable.
It's also anti-coccidiosis, I never had a single bird show symptoms much less die from it, because I fed raw garlic from day one of their lives (unless they started eating at day 2 which is pretty normal but you get what I mean, lol)...
I raised all my birds free range and naturally, no chemicals or anything artificial like that, and have (not counting a few predator deaths and a few losses to inherited Leukosis) a 100% ratio of chicks hatched making it to adulthood, in a mixed and free range integrated flock, kept on the same ground for year after year after year. So something is clearly working, lol. But if you're skeptical I understand, I was too initially; most people are too skeptical to even try it, they stick with conventional treatments which save some but not all rather than try something not commercially advertised and sponsored.
About the ground: I highly recommend you use hydrated agricultural lime powder and sprinkle the whole ground area, anywhere the birds go. It kills many damaging things like harmful fungi and bacteria and diseases and it burns parasite eggs to death.
I'd also put unpasteurized Apple Cider Vinegar (with the 'mother') in the water, in at least one water source, to help them (it does a whole host of good things for them, google it if you like or ask for more info). Fermenting or at least soaking their grains means they absorb much, much more of it, so it saves you feed costs and their health will be glowing.
Best wishes.
