It can help to not get hatchery stock, they generally have very little resistance to anything because they're reared on medicated foods with antibiotics under controlled and often over-sterilized environments, so they cannot cope well in more natural environments. But backyard breeders often have bodgy stock too. Always good to be able to view the parents and know what sort of conditions they've reproduced and survived under, and for how many generations.
Over-protecting your turkeys will only make them weaker, but it is a long hard road with many losses involved to take weakly stock up to strength and resilience. Not for everyone. If you have both chickens and turkeys, good to work on resistance. If you only have turkeys out in some remote place where they'll never be exposed to other poultry, you can get away with keeping weakly stock in good health for longer. Many turkeys are only as healthy as their environment is safe, which is unrealistic and unsustainable. But, different strokes for different folks, it can be heartbreaking for people to repeatedly lose their turkeys over and over again.
Best wishes.
